20012016 Ericsson AB. All Rights Reserved. Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. erl_nif Sverker Eriksson Sverker Eriksson 1 2009-11-17 PA1 erl_nif.xml
erl_nif API functions for an Erlang NIF library.

A NIF library contains native implementation of some functions of an Erlang module. The native implemented functions (NIFs) are called like any other functions without any difference to the caller. Each NIF must have an implementation in Erlang that is invoked if the function is called before the NIF library is successfully loaded. A typical such stub implementation is to throw an exception. But it can also be used as a fallback implementation if the NIF library is not implemented for some architecture.

Use this functionality with extreme care.

A native function is executed as a direct extension of the native code of the VM. Execution is not made in a safe environment. The VM cannot provide the same services as provided when executing Erlang code, such as pre-emptive scheduling or memory protection. If the native function does not behave well, the whole VM will misbehave.

A native function that crash will crash the whole VM.

An erroneously implemented native function can cause a VM internal state inconsistency, which can cause a crash of the VM, or miscellaneous misbehaviors of the VM at any point after the call to the native function.

A native function doing lengthy work before returning degrades responsiveness of the VM, and can cause miscellaneous strange behaviors. Such strange behaviors include, but are not limited to, extreme memory usage, and bad load balancing between schedulers. Strange behaviors that can occur because of lengthy work can also vary between Erlang/OTP releases.

A minimal example of a NIF library can look as follows:

/* niftest.c */ #include <erl_nif.h> static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]) { return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1); } static ErlNifFunc nif_funcs[] = { {"hello", 0, hello} }; ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)

The Erlang module can look as follows:

-module(niftest). -export([init/0, hello/0]). init() -> erlang:load_nif("./niftest", 0). hello() -> "NIF library not loaded".

Compile and test can look as follows (on Linux):

$> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/ $> erl 1> c(niftest). {ok,niftest} 2> niftest:hello(). "NIF library not loaded" 3> niftest:init(). ok 4> niftest:hello(). "Hello world!"

A better solution for a real module is to take advantage of the new directive on_load (see section Running a Function When a Module is Loaded in the Erlang Reference Manual) to load the NIF library automatically when the module is loaded.

A NIF does not have to be exported, it can be local to the module. However, unused local stub functions will be optimized away by the compiler, causing loading of the NIF library to fail.

Once loaded, a NIF library is persistent. It will not be unloaded until the module code version that it belongs to is purged.

Functionality

All interaction between NIF code and the Erlang runtime system is performed by calling NIF API functions. Functions exist for the following functionality:

Read and write Erlang terms

Any Erlang terms can be passed to a NIF as function arguments and be returned as function return values. The terms are of C-type ERL_NIF_TERM and can only be read or written using API functions. Most functions to read the content of a term are prefixed enif_get_ and usually return true (or false) if the term is of the expected type (or not). The functions to write terms are all prefixed enif_make_ and usually return the created ERL_NIF_TERM. There are also some functions to query terms, like enif_is_atom, enif_is_identical, and enif_compare.

All terms of type ERL_NIF_TERM belong to an environment of type ErlNifEnv. The lifetime of a term is controlled by the lifetime of its environment object. All API functions that read or write terms has the environment that the term belongs to as the first function argument.

Binaries

Terms of type binary are accessed with the help of struct type ErlNifBinary, which contains a pointer (data) to the raw binary data and the length (size) of the data in bytes. Both data and size are read-only and are only to be written using calls to API functions. Instances of ErlNifBinary are, however, always allocated by the user (usually as local variables).

The raw data pointed to by data is only mutable after a call to enif_alloc_binary or enif_realloc_binary. All other functions that operate on a binary leave the data as read-only. A mutable binary must in the end either be freed with enif_release_binary or made read-only by transferring it to an Erlang term with enif_make_binary. However, it does not have to occur in the same NIF call. Read-only binaries do not have to be released.

enif_make_new_binary can be used as a shortcut to allocate and return a binary in the same NIF call.

Binaries are sequences of whole bytes. Bitstrings with an arbitrary bit length have no support yet.

Resource objects

The use of resource objects is a safe way to return pointers to native data structures from a NIF. A resource object is only a block of memory allocated with enif_alloc_resource. A handle ("safe pointer") to this memory block can then be returned to Erlang by the use of enif_make_resource. The term returned by enif_make_resource is opaque in nature. It can be stored and passed between processes on the same node, but the only real end usage is to pass it back as an argument to a NIF. The NIF can then call enif_get_resource and get back a pointer to the memory block, which is guaranteed to still be valid. A resource object is not deallocated until the last handle term is garbage collected by the VM and the resource is released with enif_release_resource (not necessarily in that order).

All resource objects are created as instances of some resource type. This makes resources from different modules to be distinguishable. A resource type is created by calling enif_open_resource_type when a library is loaded. Objects of that resource type can then later be allocated and enif_get_resource verifies that the resource is of the expected type. A resource type can have a user-supplied destructor function, which is automatically called when resources of that type are released (by either the garbage collector or enif_release_resource). Resource types are uniquely identified by a supplied name string and the name of the implementing module.

The following is a template example of how to create and return a resource object.

ERL_NIF_TERM term; MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct)); /* initialize struct ... */ term = enif_make_resource(env, obj); if (keep_a_reference_of_our_own) { /* store 'obj' in static variable, private data or other resource object */ } else { enif_release_resource(obj); /* resource now only owned by "Erlang" */ } return term;

Notice that once enif_make_resource creates the term to return to Erlang, the code can choose to either keep its own native pointer to the allocated struct and release it later, or release it immediately and rely only on the garbage collector to deallocate the resource object eventually when it collects the term.

Another use of resource objects is to create binary terms with user-defined memory management. enif_make_resource_binary creates a binary term that is connected to a resource object. The destructor of the resource is called when the binary is garbage collected, at which time the binary data can be released. An example of this can be a binary term consisting of data from a mmap'ed file. The destructor can then do munmap to release the memory region.

Resource types support upgrade in runtime by allowing a loaded NIF library to take over an already existing resource type and by that "inherit" all existing objects of that type. The destructor of the new library is thereafter called for the inherited objects and the library with the old destructor function can be safely unloaded. Existing resource objects, of a module that is upgraded, must either be deleted or taken over by the new NIF library. The unloading of a library is postponed as long as there exist resource objects with a destructor function in the library.

Module upgrade and static data

A loaded NIF library is tied to the Erlang module instance that loaded it. If the module is upgraded, the new module instance needs to load its own NIF library (or maybe choose not to). The new module instance can, however, choose to load the exact same NIF library as the old code if it wants to. Sharing the dynamic library means that static data defined by the library is shared as well. To avoid unintentionally shared static data between module instances, each Erlang module version can keep its own private data. This private data can be set when the NIF library is loaded and later retrieved by calling enif_priv_data.

Threads and concurrency

A NIF is thread-safe without any explicit synchronization as long as it acts as a pure function and only reads the supplied arguments. When you write to a shared state either through static variables or enif_priv_data, you need to supply your own explicit synchronization. This includes terms in process-independent environments that are shared between threads. Resource objects also require synchronization if you treat them as mutable.

The library initialization callbacks load and upgrade are thread-safe even for shared state data.

Version Management

When a NIF library is built, information about the NIF API version is compiled into the library. When a NIF library is loaded, the runtime system verifies that the library is of a compatible version. erl_nif.h defines the following:

ERL_NIF_MAJOR_VERSION

Incremented when NIF library incompatible changes are made to the Erlang runtime system. Normally it suffices to recompile the NIF library when the ERL_NIF_MAJOR_VERSION has changed, but it can, under rare circumstances, mean that NIF libraries must be slightly modified. If so, this will of course be documented.

ERL_NIF_MINOR_VERSION

Incremented when new features are added. The runtime system uses the minor version to determine what features to use.

The runtime system normally refuses to load a NIF library if the major versions differ, or if the major versions are equal and the minor version used by the NIF library is greater than the one used by the runtime system. Old NIF libraries with lower major versions are, however, allowed after a bump of the major version during a transition period of two major releases. Such old NIF libraries can however fail if deprecated features are used.

Time Measurement

Support for time measurement in NIF libraries:

ErlNifTime ErlNifTimeUnit enif_monotonic_time() enif_time_offset() enif_convert_time_unit()
Long-running NIFs

As mentioned in the warning text at the beginning of this manual page, it is of vital importance that a native function returns relatively fast. It is difficult to give an exact maximum amount of time that a native function is allowed to work, but usually a well-behaving native function is to return to its caller within 1 millisecond. This can be achieved using different approaches. If you have full control over the code to execute in the native function, the best approach is to divide the work into multiple chunks of work and call the native function multiple times. This is, however, not always possible, for example when calling third-party libraries.

The enif_consume_timeslice() function can be used to inform the runtime system about the length of the NIF call. It is typically always to be used unless the NIF executes very fast.

If the NIF call is too lengthy, this must be handled in one of the following ways to avoid degraded responsiveness, scheduler load balancing problems, and other strange behaviors:

Yielding NIF

If the functionality of a long-running NIF can be split so that its work can be achieved through a series of shorter NIF calls, the application has two options:

Make that series of NIF calls from the Erlang level.

Call a NIF that first performs a chunk of the work, then invokes the enif_schedule_nif function to schedule another NIF call to perform the next chunk. The final call scheduled in this manner can then return the overall result.

Breaking up a long-running function in this manner enables the VM to regain control between calls to the NIFs.

This approach is always preferred over the other alternatives described below. This both from a performance perspective and a system characteristics perspective.

Threaded NIF

This is accomplished by dispatching the work to another thread managed by the NIF library, return from the NIF, and wait for the result. The thread can send the result back to the Erlang process using enif_send. Information about thread primitives is provided below.

Dirty NIF

Dirty NIF support is available only when the emulator is configured with dirty scheduler support. As of ERTS version 9.0, dirty scheduler support is enabled by default on the runtime system with SMP support. The Erlang runtime without SMP support does not support dirty schedulers even when the dirty scheduler support is explicitly enabled. To check at runtime for the presence of dirty scheduler threads, code can use the enif_system_info() API function.

A NIF that cannot be split and cannot execute in a millisecond or less is called a "dirty NIF", as it performs work that the ordinary schedulers of the Erlang runtime system cannot handle cleanly. Applications that make use of such functions must indicate to the runtime that the functions are dirty so they can be handled specially. This is handled by executing dirty jobs on a separate set of schedulers called dirty schedulers. A dirty NIF executing on a dirty scheduler does not have the same duration restriction as a normal NIF.

It is important to classify the dirty job correct. An I/O bound job should be classified as such, and a CPU bound job should be classified as such. If you should classify CPU bound jobs as I/O bound jobs, dirty I/O schedulers might starve ordinary schedulers. I/O bound jobs are expected to either block waiting for I/O, and/or spend a limited amount of time moving data.

To schedule a dirty NIF for execution, the application has two options:

Set the appropriate flags value for the dirty NIF in its ErlNifFunc entry.

Call enif_schedule_nif, pass to it a pointer to the dirty NIF to be executed, and indicate with argument flags whether it expects the operation to be CPU-bound or I/O-bound.

A job that alternates between I/O bound and CPU bound can be reclassified and rescheduled using enif_schedule_nif so that it executes on the correct type of dirty scheduler at all times. For more information see the documentation of the erl(1) command line arguments +SDcpu, and +SDio.

While a process executes a dirty NIF, some operations that communicate with it can take a very long time to complete. Suspend or garbage collection of a process executing a dirty NIF cannot be done until the dirty NIF has returned. Thus, other processes waiting for such operations to complete might have to wait for a very long time. Blocking multi-scheduling, that is, calling erlang:system_flag(multi_scheduling, block), can also take a very long time to complete. This becaue all ongoing dirty operations on all dirty schedulers must complete before the block operation can complete.

Many operations communicating with a process executing a dirty NIF can, however, complete while it executes the dirty NIF. For example, retrieving information about it through erlang:process_info, setting its group leader, register/unregister its name, and so on.

Termination of a process executing a dirty NIF can only be completed up to a certain point while it executes the dirty NIF. All Erlang resources, such as its registered name and its ETS tables, are released. All links and monitors are triggered. The execution of the NIF is, however, not stopped. The NIF can safely continue execution, allocate heap memory, and so on, but it is of course better to stop executing as soon as possible. The NIF can check whether a current process is alive using enif_is_current_process_alive. Communication using enif_send and enif_port_command is also dropped when the sending process is not alive. Deallocation of certain internal resources, such as process heap and process control block, is delayed until the dirty NIF has completed.

Initialization ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, NULL, upgrade, unload)

This is the magic macro to initialize a NIF library. It is to be evaluated in global file scope.

MODULE is the name of the Erlang module as an identifier without string quotations. It is stringified by the macro.

funcs is a static array of function descriptors for all the implemented NIFs in this library.

load, upgrade and unload are pointers to functions. One of load or upgrade is called to initialize the library. unload is called to release the library. All are described individually below.

The fourth argument NULL is ignored. It was earlier used for the deprectated reload callback which is no longer supported since OTP 20.

If compiling a NIF for static inclusion through --enable-static-nifs, you must define STATIC_ERLANG_NIF before the ERL_NIF_INIT declaration.

int (*load)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)

load is called when the NIF library is loaded and no previously loaded library exists for this module.

*priv_data can be set to point to some private data if the library needs to keep a state between NIF calls. enif_priv_data returns this pointer. *priv_data is initialized to NULL when load is called.

load_info is the second argument to erlang:load_nif/2.

The library fails to load if load returns anything other than 0. load can be NULL if initialization is not needed.

int (*upgrade)(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info)

upgrade is called when the NIF library is loaded and there is old code of this module with a loaded NIF library.

Works as load, except that *old_priv_data already contains the value set by the last call to load or upgrade for the old module code. *priv_data is initialized to NULL when upgrade is called. It is allowed to write to both *priv_data and *old_priv_data.

The library fails to load if upgrade returns anything other than 0 or if upgrade is NULL.

void (*unload)(ErlNifEnv* env, void* priv_data)

unload is called when the module code that the NIF library belongs to is purged as old. New code of the same module may or may not exist.

Data Types ERL_NIF_TERM

Variables of type ERL_NIF_TERM can refer to any Erlang term. This is an opaque type and values of it can only by used either as arguments to API functions or as return values from NIFs. All ERL_NIF_TERMs belong to an environment (ErlNifEnv). A term cannot be destructed individually, it is valid until its environment is destructed.

ErlNifEnv

ErlNifEnv represents an environment that can host Erlang terms. All terms in an environment are valid as long as the environment is valid. ErlNifEnv is an opaque type; pointers to it can only be passed on to API functions. Two types of environments exist:

Process-bound environment

Passed as the first argument to all NIFs. All function arguments passed to a NIF belong to that environment. The return value from a NIF must also be a term belonging to the same environment.

A process-bound environment contains transient information about the calling Erlang process. The environment is only valid in the thread where it was supplied as argument until the NIF returns. It is thus useless and dangerous to store pointers to process-bound environments between NIF calls.

Process-independent environment

Created by calling enif_alloc_env. This environment can be used to store terms between NIF calls and to send terms with enif_send. A process-independent environment with all its terms is valid until you explicitly invalidate it with enif_free_env or enif_send.

All contained terms of a list/tuple/map must belong to the same environment as the list/tuple/map itself. Terms can be copied between environments with enif_make_copy.

ErlNifFunc typedef struct { const char* name; unsigned arity; ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]); unsigned flags; } ErlNifFunc;

Describes a NIF by its name, arity, and implementation.

fptr

A pointer to the function that implements the NIF.

argv

Contains the function arguments passed to the NIF.

argc

The array length, that is, the function arity. argv[N-1] thus denotes the Nth argument to the NIF. Notice that the argument argc allows for the same C function to implement several Erlang functions with different arity (but probably with the same name).

flags

Is 0 for a regular NIF (and so its value can be omitted for statically initialized ErlNifFunc instances).

flags can be used to indicate that the NIF is a dirty NIF that is to be executed on a dirty scheduler thread.

If the dirty NIF is expected to be CPU-bound, its flags field is to be set to ERL_NIF_DIRTY_JOB_CPU_BOUND or ERL_NIF_DIRTY_JOB_IO_BOUND.

If one of the ERL_NIF_DIRTY_JOB_*_BOUND flags is set, and the runtime system has no support for dirty schedulers, the runtime system refuses to load the NIF library.

ErlNifBinary typedef struct { unsigned size; unsigned char* data; } ErlNifBinary;

ErlNifBinary contains transient information about an inspected binary term. data is a pointer to a buffer of size bytes with the raw content of the binary.

Notice that ErlNifBinary is a semi-opaque type and you are only allowed to read fields size and data.

ErlNifBinaryToTerm

An enumeration of the options that can be specified to enif_binary_to_term. For default behavior, use value 0.

When receiving data from untrusted sources, use option ERL_NIF_BIN2TERM_SAFE.

ErlNifPid

A process identifier (pid). In contrast to pid terms (instances of ERL_NIF_TERM), ErlNifPids are self-contained and not bound to any environment. ErlNifPid is an opaque type.

ErlNifPort

A port identifier. In contrast to port ID terms (instances of ERL_NIF_TERM), ErlNifPorts are self-contained and not bound to any environment. ErlNifPort is an opaque type.

ErlNifResourceType

Each instance of ErlNifResourceType represents a class of memory-managed resource objects that can be garbage collected. Each resource type has a unique name and a destructor function that is called when objects of its type are released.

ErlNifResourceTypeInit typedef struct { ErlNifResourceDtor* dtor; ErlNifResourceStop* stop; } ErlNifResourceTypeInit;

Initialization structure read by enif_open_resource_type_x.

ErlNifResourceDtor typedef void ErlNifResourceDtor(ErlNifEnv* env, void* obj);

The function prototype of a resource destructor function.

The obj argument is a pointer to the resource. The only allowed use for the resource in the destructor is to access its user data one final time. The destructor is guaranteed to be the last callback before the resource is deallocated.

ErlNifResourceDown typedef void ErlNifResourceDown(ErlNifEnv* env, void* obj, const ErlNifPid* pid, const ErlNifMonitor* mon);

The function prototype of a resource down function, called on the behalf of enif_monitor_process. obj is the resource, pid is the identity of the monitored process that is exiting, and mon is the identity of the monitor.

ErlNifResourceStop typedef void ErlNifResourceStop(ErlNifEnv* env, void* obj, ErlNifEvent event, int is_direct_call);

The function prototype of a resource stop function, called on the behalf of enif_select. obj is the resource, event is OS event, is_direct_call is true if the call is made directly from enif_select or false if it is a scheduled call (potentially from another thread).

ErlNifCharEncoding typedef enum { ERL_NIF_LATIN1 }ErlNifCharEncoding;

The character encoding used in strings and atoms. The only supported encoding is ERL_NIF_LATIN1 for ISO Latin-1 (8-bit ASCII).

ErlNifSysInfo

Used by enif_system_info to return information about the runtime system. Contains the same content as ErlDrvSysInfo.

ErlNifSInt64

A native signed 64-bit integer type.

ErlNifUInt64

A native unsigned 64-bit integer type.

ErlNifTime

A signed 64-bit integer type for representation of time.

ErlNifTimeUnit

An enumeration of time units supported by the NIF API:

ERL_NIF_SEC Seconds ERL_NIF_MSEC Milliseconds ERL_NIF_USEC Microseconds ERL_NIF_NSEC Nanoseconds
ErlNifUniqueInteger

An enumeration of the properties that can be requested from enif_unique_integer. For default properties, use value 0.

ERL_NIF_UNIQUE_POSITIVE

Return only positive integers.

ERL_NIF_UNIQUE_MONOTONIC

Return only strictly monotonically increasing integer corresponding to creation time.

void *enif_alloc(size_t size) Allocate dynamic memory.

Allocates memory of size bytes.

Returns NULL if the allocation fails.

int enif_alloc_binary(size_t size, ErlNifBinary* bin) Create a new binary.

Allocates a new binary of size size bytes. Initializes the structure pointed to by bin to refer to the allocated binary. The binary must either be released by enif_release_binary or ownership transferred to an Erlang term with enif_make_binary. An allocated (and owned) ErlNifBinary can be kept between NIF calls.

Returns true on success, or false if allocation fails.

ErlNifEnv *enif_alloc_env() Create a new environment.

Allocates a new process-independent environment. The environment can be used to hold terms that are not bound to any process. Such terms can later be copied to a process environment with enif_make_copy or be sent to a process as a message with enif_send.

Returns pointer to the new environment.

void *enif_alloc_resource(ErlNifResourceType* type, unsigned size) Allocate a memory-managed resource object.

Allocates a memory-managed resource object of type type and size size bytes.

size_tenif_binary_to_term(ErlNifEnv *env, const unsigned char* data, size_t size, ERL_NIF_TERM *term, ErlNifBinaryToTerm opts) Create a term from the external format.

Creates a term that is the result of decoding the binary data at data, which must be encoded according to the Erlang external term format. No more than size bytes are read from data. Argument opts corresponds to the second argument to erlang:binary_to_term/2 and must be either 0 or ERL_NIF_BIN2TERM_SAFE.

On success, stores the resulting term at *term and returns the number of bytes read. Returns 0 if decoding fails or if opts is invalid.

See also ErlNifBinaryToTerm, erlang:binary_to_term/2, and enif_term_to_binary.

voidenif_clear_env(ErlNifEnv* env) Clear an environment for reuse.

Frees all terms in an environment and clears it for reuse. The environment must have been allocated with enif_alloc_env.

int enif_compare(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs) Compare two terms.

Returns an integer < 0 if lhs < rhs, 0 if lhs = rhs, and > 0 if lhs > rhs. Corresponds to the Erlang operators ==, /=, =<, <, >=, and > (but not =:= or =/=).

void enif_cond_broadcast(ErlNifCond *cnd)

Same as erl_drv_cond_broadcast.

ErlNifCond * enif_cond_create(char *name)

Same as erl_drv_cond_create.

void enif_cond_destroy(ErlNifCond *cnd)

Same as erl_drv_cond_destroy.

void enif_cond_signal(ErlNifCond *cnd)

Same as erl_drv_cond_signal.

void enif_cond_wait(ErlNifCond *cnd, ErlNifMutex *mtx)

Same as erl_drv_cond_wait.

int enif_consume_timeslice(ErlNifEnv *env, int percent)

Gives the runtime system a hint about how much CPU time the current NIF call has consumed since the last hint, or since the start of the NIF if no previous hint has been specified. The time is specified as a percent of the timeslice that a process is allowed to execute Erlang code until it can be suspended to give time for other runnable processes. The scheduling timeslice is not an exact entity, but can usually be approximated to about 1 millisecond.

Notice that it is up to the runtime system to determine if and how to use this information. Implementations on some platforms can use other means to determine consumed CPU time. Lengthy NIFs should regardless of this frequently call enif_consume_timeslice to determine if it is allowed to continue execution.

Argument percent must be an integer between 1 and 100. This function must only be called from a NIF-calling thread, and argument env must be the environment of the calling process.

Returns 1 if the timeslice is exhausted, otherwise 0. If 1 is returned, the NIF is to return as soon as possible in order for the process to yield.

This function is provided to better support co-operative scheduling, improve system responsiveness, and make it easier to prevent misbehaviors of the VM because of a NIF monopolizing a scheduler thread. It can be used to divide length work into a number of repeated NIF calls without the need to create threads.

See also the warning text at the beginning of this manual page.

ErlNifTimeenif_convert_time_unit(ErlNifTime val, ErlNifTimeUnit from, ErlNifTimeUnit to) Convert time unit of a time value.

Converts the val value of time unit from to the corresponding value of time unit to. The result is rounded using the floor function.

val Value to convert time unit for. from Time unit of val. to Time unit of returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument.

See also ErlNifTime and ErlNifTimeUnit.

ERL_NIF_TERM enif_cpu_time(ErlNifEnv *)

Returns the CPU time in the same format as erlang:timestamp(). The CPU time is the time the current logical CPU has spent executing since some arbitrary point in the past. If the OS does not support fetching this value, enif_cpu_time invokes enif_make_badarg.

intenif_demonitor_process(ErlNifEnv* env, void* obj, const ErlNifMonitor* mon) Cancel a process monitor.

Cancels a monitor created earlier with enif_monitor_process. Argument obj is a pointer to the resource holding the monitor and *mon identifies the monitor.

Returns 0 if the monitor was successfully identified and removed. Returns a non-zero value if the monitor could not be identified, which means it was either

never created for this resource already triggered just about to be triggered by a concurrent thread

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

int enif_equal_tids(ErlNifTid tid1, ErlNifTid tid2)

Same as erl_drv_equal_tids.

voidenif_free(void* ptr) Free dynamic memory.

Frees memory allocated by enif_alloc.

void enif_free_env(ErlNifEnv* env) Free an environment allocated with enif_alloc_env.

Frees an environment allocated with enif_alloc_env. All terms created in the environment are freed as well.

intenif_get_atom(ErlNifEnv* env, ERL_NIF_TERM term, char* buf, unsigned size, ErlNifCharEncoding encode) Get the text representation of an atom term.

Writes a NULL-terminated string in the buffer pointed to by buf of size size, consisting of the string representation of the atom term with encoding encode.

Returns the number of bytes written (including terminating NULL character) or 0 if term is not an atom with maximum length of size-1.

intenif_get_atom_length(ErlNifEnv* env, ERL_NIF_TERM term, unsigned* len, ErlNifCharEncoding encode) Get the length of atom term.

Sets *len to the length (number of bytes excluding terminating NULL character) of the atom term with encoding encode.

Returns true on success, or false if term is not an atom.

intenif_get_double(ErlNifEnv* env, ERL_NIF_TERM term, double* dp) Read a floating-point number term.

Sets *dp to the floating-point value of term.

Returns true on success, or false if term is not a float.

intenif_get_int(ErlNifEnv* env, ERL_NIF_TERM term, int* ip) Read an integer term.

Sets *ip to the integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of type int.

intenif_get_int64(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifSInt64* ip) Read a 64-bit integer term.

Sets *ip to the integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of a signed 64-bit integer.

intenif_get_local_pid(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifPid* pid) Read a local pid term.

If term is the pid of a node local process, this function initializes the pid variable *pid from it and returns true. Otherwise returns false. No check is done to see if the process is alive.

intenif_get_local_port(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifPort* port_id) Read a local port term.

If term identifies a node local port, this function initializes the port variable *port_id from it and returns true. Otherwise returns false. No check is done to see if the port is alive.

intenif_get_list_cell(ErlNifEnv* env, ERL_NIF_TERM list, ERL_NIF_TERM* head, ERL_NIF_TERM* tail) Get head and tail from a list.

Sets *head and *tail from list list.

Returns true on success, or false if it is not a list or the list is empty.

intenif_get_list_length(ErlNifEnv* env, ERL_NIF_TERM term, unsigned* len) Get the length of list term.

Sets *len to the length of list term.

Returns true on success, or false if term is not a proper list.

intenif_get_long(ErlNifEnv* env, ERL_NIF_TERM term, long int* ip) Read a long integer term.

Sets *ip to the long integer value of term.

Returns true on success, or false if term is not an integer or is outside the bounds of type long int.

intenif_get_map_size(ErlNifEnv* env, ERL_NIF_TERM term, size_t *size) Read the size of a map term.

Sets *size to the number of key-value pairs in the map term.

Returns true on success, or false if term is not a map.

intenif_get_map_value(ErlNifEnv* env, ERL_NIF_TERM map, ERL_NIF_TERM key, ERL_NIF_TERM* value) Get the value of a key in a map.

Sets *value to the value associated with key in the map map.

Returns true on success, or false if map is not a map or if map does not contain key.

intenif_get_resource(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifResourceType* type, void** objp) Get the pointer to a resource object.

Sets *objp to point to the resource object referred to by term.

Returns true on success, or false if term is not a handle to a resource object of type type.

intenif_get_string(ErlNifEnv* env, ERL_NIF_TERM list, char* buf, unsigned size, ErlNifCharEncoding encode) Get a C-string from a list.

Writes a NULL-terminated string in the buffer pointed to by buf with size size, consisting of the characters in the string list. The characters are written using encoding encode.

Returns one of the following:

The number of bytes written (including terminating NULL character) -size if the string was truncated because of buffer space 0 if list is not a string that can be encoded with encode or if size was < 1.

The written string is always NULL-terminated, unless buffer size is < 1.

intenif_get_tuple(ErlNifEnv* env, ERL_NIF_TERM term, int* arity, const ERL_NIF_TERM** array) Inspect the elements of a tuple.

If term is a tuple, this function sets *array to point to an array containing the elements of the tuple, and sets *arity to the number of elements. Notice that the array is read-only and (*array)[N-1] is the Nth element of the tuple. *array is undefined if the arity of the tuple is zero.

Returns true on success, or false if term is not a tuple.

intenif_get_uint(ErlNifEnv* env, ERL_NIF_TERM term, unsigned int* ip) Read an unsigned integer term.

Sets *ip to the unsigned integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of type unsigned int.

intenif_get_uint64(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifUInt64* ip) Read an unsigned 64-bit integer term.

Sets *ip to the unsigned integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of an unsigned 64-bit integer.

intenif_get_ulong(ErlNifEnv* env, ERL_NIF_TERM term, unsigned long* ip) Read an unsigned integer term.

Sets *ip to the unsigned long integer value of term.

Returns true on success, or false if term is not an unsigned integer or is outside the bounds of type unsigned long.

intenif_getenv(const char* key, char* value, size_t *value_size) Get the value of an environment variable.

Same as erl_drv_getenv.

intenif_has_pending_exception(ErlNifEnv* env, ERL_NIF_TERM* reason) Check if an exception has been raised.

Returns true if a pending exception is associated with the environment env. If reason is a NULL pointer, ignore it. Otherwise, if a pending exception associated with env exists, set ERL_NIF_TERM to which reason points to the value of the exception's term. For example, if enif_make_badarg is called to set a pending badarg exception, a later call to enif_has_pending_exception(env, &reason) sets reason to the atom badarg, then return true.

See also enif_make_badarg and enif_raise_exception.

intenif_inspect_binary(ErlNifEnv* env, ERL_NIF_TERM bin_term, ErlNifBinary* bin) Inspect the content of a binary.

Initializes the structure pointed to by bin with information about binary term bin_term.

Returns true on success, or false if bin_term is not a binary.

intenif_inspect_iolist_as_binary(ErlNifEnv* env, ERL_NIF_TERM term, ErlNifBinary* bin) Inspect the content of an iolist.

Initializes the structure pointed to by bin with a continuous buffer with the same byte content as iolist. As with inspect_binary, the data pointed to by bin is transient and does not need to be released.

Returns true on success, or false if iolist is not an iolist.

int enif_is_atom(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is an atom.

Returns true if term is an atom.

int enif_is_binary(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a binary.

Returns true if term is a binary.

int enif_is_current_process_alive(ErlNifEnv* env) Determine if currently executing process is alive.

Returns true if the currently executing process is currently alive, otherwise false.

This function can only be used from a NIF-calling thread, and with an environment corresponding to currently executing processes.

intenif_is_empty_list(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is an empty list.

Returns true if term is an empty list.

intenif_is_exception(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is an exception.

Return true if term is an exception.

intenif_is_fun(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a fun.

Returns true if term is a fun.

intenif_is_identical(ERL_NIF_TERM lhs, ERL_NIF_TERM rhs) Erlang operator =:=.

Returns true if the two terms are identical. Corresponds to the Erlang operators =:= and =/=.

int enif_is_list(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a list.

Returns true if term is a list.

intenif_is_map(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a map.

Returns true if term is a map, otherwise false.

intenif_is_number(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a number (integer or float).

Returns true if term is a number.

int enif_is_pid(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a pid.

Returns true if term is a pid.

int enif_is_port(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a port.

Returns true if term is a port.

intenif_is_port_alive(ErlNifEnv* env, ErlNifPort *port_id) Determine if a local port is alive.

Returns true if port_id is alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

intenif_is_process_alive(ErlNifEnv* env, ErlNifPid *pid) Determine if a local process is alive.

Returns true if pid is alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

int enif_is_ref(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a reference.

Returns true if term is a reference.

int enif_is_tuple(ErlNifEnv* env, ERL_NIF_TERM term) Determine if a term is a tuple.

Returns true if term is a tuple.

int enif_keep_resource(void* obj) Add a reference to a resource object.

Adds a reference to resource object obj obtained from enif_alloc_resource. Each call to enif_keep_resource for an object must be balanced by a call to enif_release_resource before the object is destructed.

ERL_NIF_TERM enif_make_atom(ErlNifEnv* env, const char* name) Create an atom term.

Creates an atom term from the NULL-terminated C-string name with ISO Latin-1 encoding. If the length of name exceeds the maximum length allowed for an atom (255 characters), enif_make_atom invokes enif_make_badarg.

ERL_NIF_TERMenif_make_atom_len(ErlNifEnv* env, const char* name, size_t len) Create an atom term.

Create an atom term from the string name with length len. NULL characters are treated as any other characters. If len exceeds the maximum length allowed for an atom (255 characters), enif_make_atom invokes enif_make_badarg.

ERL_NIF_TERM enif_make_badarg(ErlNifEnv* env) Make a badarg exception.

Makes a badarg exception to be returned from a NIF, and associates it with environment env. Once a NIF or any function it calls invokes enif_make_badarg, the runtime ensures that a badarg exception is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.

The return value from enif_make_badarg can be used only as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception, but not to any other NIF API function.

See also enif_has_pending_exception and enif_raise_exception.

Before ERTS 7.0 (Erlang/OTP 18), the return value from enif_make_badarg had to be returned from the NIF. This requirement is now lifted as the return value from the NIF is ignored if enif_make_badarg has been invoked.

ERL_NIF_TERM enif_make_binary(ErlNifEnv* env, ErlNifBinary* bin) Make a binary term.

Makes a binary term from bin. Any ownership of the binary data is transferred to the created term and bin is to be considered read-only for the rest of the NIF call and then as released.

ERL_NIF_TERMenif_make_copy(ErlNifEnv* dst_env, ERL_NIF_TERM src_term) Make a copy of a term.

Makes a copy of term src_term. The copy is created in environment dst_env. The source term can be located in any environment.

ERL_NIF_TERM enif_make_double(ErlNifEnv* env, double d) Create a floating-point term.

Creates a floating-point term from a double. If argument double is not finite or is NaN, enif_make_double invokes enif_make_badarg.

intenif_make_existing_atom(ErlNifEnv* env, const char* name, ERL_NIF_TERM* atom, ErlNifCharEncoding encode) Create an existing atom term.

Tries to create the term of an already existing atom from the NULL-terminated C-string name with encoding encode.

If the atom already exists, this function stores the term in *atom and returns true, otherwise false. Also returns false if the length of name exceeds the maximum length allowed for an atom (255 characters).

intenif_make_existing_atom_len(ErlNifEnv* env, const char* name, size_t len, ERL_NIF_TERM* atom, ErlNifCharEncoding encoding) Create an existing atom term.

Tries to create the term of an already existing atom from the string name with length len and encoding encode. NULL characters are treated as any other characters.

If the atom already exists, this function stores the term in *atom and returns true, otherwise false. Also returns false if len exceeds the maximum length allowed for an atom (255 characters).

ERL_NIF_TERM enif_make_int(ErlNifEnv* env, int i) Create an integer term.

Creates an integer term.

ERL_NIF_TERM enif_make_int64(ErlNifEnv* env, ErlNifSInt64 i) Create an integer term.

Creates an integer term from a signed 64-bit integer.

ERL_NIF_TERM enif_make_list(ErlNifEnv* env, unsigned cnt, ...) Create a list term.

Creates an ordinary list term of length cnt. Expects cnt number of arguments (after cnt) of type ERL_NIF_TERM as the elements of the list.

Returns an empty list if cnt is 0.

ERL_NIF_TERM enif_make_list1(ErlNifEnv* env, ERL_NIF_TERM e1) ERL_NIF_TERMenif_make_list2(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2) ERL_NIF_TERMenif_make_list3(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3) ERL_NIF_TERMenif_make_list4(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4) ERL_NIF_TERMenif_make_list5(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5) ERL_NIF_TERMenif_make_list6(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6) ERL_NIF_TERMenif_make_list7(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7) ERL_NIF_TERMenif_make_list8(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8) ERL_NIF_TERMenif_make_list9(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9) Create a list term.

Creates an ordinary list term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_list to get a compile-time error if the number of arguments does not match.

ERL_NIF_TERMenif_make_list_cell(ErlNifEnv* env, ERL_NIF_TERM head, ERL_NIF_TERM tail) Create a list cell.

Creates a list cell [head | tail].

ERL_NIF_TERM enif_make_list_from_array(ErlNifEnv* env, const ERL_NIF_TERM arr[], unsigned cnt) Create a list term from an array.

Creates an ordinary list containing the elements of array arr of length cnt.

Returns an empty list if cnt is 0.

ERL_NIF_TERM enif_make_long(ErlNifEnv* env, long int i) Create an integer term from a long int.

Creates an integer term from a long int.

intenif_make_map_put(ErlNifEnv* env, ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM value, ERL_NIF_TERM* map_out) Insert key-value pair in map.

Makes a copy of map map_in and inserts key with value. If key already exists in map_in, the old associated value is replaced by value.

If successful, this function sets *map_out to the new map and returns true. Returns false if map_in is not a map.

The map_in term must belong to environment env.

intenif_make_map_remove(ErlNifEnv* env, ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM* map_out) Remove key from map.

If map map_in contains key, this function makes a copy of map_in in *map_out, and removes key and the associated value. If map map_in does not contain key, *map_out is set to map_in.

Returns true on success, or false if map_in is not a map.

The map_in term must belong to environment env.

intenif_make_map_update(ErlNifEnv* env, ERL_NIF_TERM map_in, ERL_NIF_TERM key, ERL_NIF_TERM new_value, ERL_NIF_TERM* map_out) Replace value for key in map.

Makes a copy of map map_in and replace the old associated value for key with new_value.

If successful, this function sets *map_out to the new map and returns true. Returns false if map_in is not a map or if it does not contain key.

The map_in term must belong to environment env.

unsigned char *enif_make_new_binary(ErlNifEnv* env, size_t size, ERL_NIF_TERM* termp) Allocate and create a new binary term.

Allocates a binary of size size bytes and creates an owning term. The binary data is mutable until the calling NIF returns. This is a quick way to create a new binary without having to use ErlNifBinary. The drawbacks are that the binary cannot be kept between NIF calls and it cannot be reallocated.

Returns a pointer to the raw binary data and sets *termp to the binary term.

ERL_NIF_TERM enif_make_new_map(ErlNifEnv* env) Make an empty map term.

Makes an empty map term.

ERL_NIF_TERM enif_make_pid(ErlNifEnv* env, const ErlNifPid* pid) Make a pid term.

Makes a pid term from *pid.

ERL_NIF_TERM enif_make_ref(ErlNifEnv* env) Create a reference.

Creates a reference like erlang:make_ref/0.

ERL_NIF_TERM enif_make_resource(ErlNifEnv* env, void* obj) Create an opaque handle to a resource object.

Creates an opaque handle to a memory-managed resource object obtained by enif_alloc_resource. No ownership transfer is done, as the resource object still needs to be released by enif_release_resource. However, notice that the call to enif_release_resource can occur immediately after obtaining the term from enif_make_resource, in which case the resource object is deallocated when the term is garbage collected. For more details, see the example of creating and returning a resource object in the User's Guide.

Notice that the only defined behavior of using a resource term in an Erlang program is to store it and send it between processes on the same node. Other operations, such as matching or term_to_binary, have unpredictable (but harmless) results.

ERL_NIF_TERM enif_make_resource_binary(ErlNifEnv* env, void* obj, const void* data, size_t size) Create a custom binary term.

Creates a binary term that is memory-managed by a resource object obj obtained by enif_alloc_resource. The returned binary term consists of size bytes pointed to by data. This raw binary data must be kept readable and unchanged until the destructor of the resource is called. The binary data can be stored external to the resource object, in which case the destructor is responsible for releasing the data.

Several binary terms can be managed by the same resource object. The destructor is not called until the last binary is garbage collected. This can be useful to return different parts of a larger binary buffer.

As with enif_make_resource, no ownership transfer is done. The resource still needs to be released with enif_release_resource.

int enif_make_reverse_list(ErlNifEnv* env, ERL_NIF_TERM list_in, ERL_NIF_TERM *list_out) Create the reverse of a list.

Sets *list_out to the reverse list of the list list_in and returns true, or returns false if list_in is not a list.

This function is only to be used on short lists, as a copy is created of the list, which is not released until after the NIF returns.

The list_in term must belong to environment env.

ERL_NIF_TERMenif_make_string(ErlNifEnv* env, const char* string, ErlNifCharEncoding encoding) Create a string.

Creates a list containing the characters of the NULL-terminated string string with encoding encoding.

ERL_NIF_TERMenif_make_string_len(ErlNifEnv* env, const char* string, size_t len, ErlNifCharEncoding encoding) Create a string.

Creates a list containing the characters of the string string with length len and encoding encoding. NULL characters are treated as any other characters.

ERL_NIF_TERMenif_make_sub_binary(ErlNifEnv* env, ERL_NIF_TERM bin_term, size_t pos, size_t size) Make a subbinary term.

Makes a subbinary of binary bin_term, starting at zero-based position pos with a length of size bytes. bin_term must be a binary or bitstring. pos+size must be less or equal to the number of whole bytes in bin_term.

ERL_NIF_TERMenif_make_tuple(ErlNifEnv* env, unsigned cnt, ...) Creates a tuple term.

Creates a tuple term of arity cnt. Expects cnt number of arguments (after cnt) of type ERL_NIF_TERM as the elements of the tuple.

ERL_NIF_TERMenif_make_tuple1(ErlNifEnv* env, ERL_NIF_TERM e1) ERL_NIF_TERMenif_make_tuple2(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2) ERL_NIF_TERMenif_make_tuple3(ErlNifEnv* env, ERL_NIF_TERM e1, ERL_NIF_TERM e2, ERL_NIF_TERM e3) ERL_NIF_TERMenif_make_tuple4(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e4) ERL_NIF_TERMenif_make_tuple5(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e5) ERL_NIF_TERMenif_make_tuple6(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e6) ERL_NIF_TERMenif_make_tuple7(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e7) ERL_NIF_TERMenif_make_tuple8(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e8) ERL_NIF_TERMenif_make_tuple9(ErlNifEnv* env, ERL_NIF_TERM e1, ..., ERL_NIF_TERM e9) Create a tuple term.

Creates a tuple term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_tuple to get a compile-time error if the number of arguments does not match.

ERL_NIF_TERM enif_make_tuple_from_array(ErlNifEnv* env, const ERL_NIF_TERM arr[], unsigned cnt) Create a tuple term from an array.

Creates a tuple containing the elements of array arr of length cnt.

ERL_NIF_TERM enif_make_uint(ErlNifEnv* env, unsigned int i) Create an unsigned integer term.

Creates an integer term from an unsigned int.

ERL_NIF_TERM enif_make_uint64(ErlNifEnv* env, ErlNifUInt64 i) Create an unsigned integer term.

Creates an integer term from an unsigned 64-bit integer.

ERL_NIF_TERM enif_make_ulong(ErlNifEnv* env, unsigned long i) Create an integer term from an unsigned long int.

Creates an integer term from an unsigned long int.

ERL_NIF_TERMenif_make_unique_integer(ErlNifEnv *env, ErlNifUniqueInteger properties)

Returns a unique integer with the same properties as specified by erlang:unique_integer/1.

env is the environment to create the integer in.

ERL_NIF_UNIQUE_POSITIVE and ERL_NIF_UNIQUE_MONOTONIC can be passed as the second argument to change the properties of the integer returned. They can be combined by OR:ing the two values together.

See also ErlNifUniqueInteger.

intenif_map_iterator_create(ErlNifEnv *env, ERL_NIF_TERM map, ErlNifMapIterator *iter, ErlNifMapIteratorEntry entry) Create a map iterator.

Creates an iterator for the map map by initializing the structure pointed to by iter. Argument entry determines the start position of the iterator: ERL_NIF_MAP_ITERATOR_FIRST or ERL_NIF_MAP_ITERATOR_LAST.

Returns true on success, or false if map is not a map.

A map iterator is only useful during the lifetime of environment env that the map belongs to. The iterator must be destroyed by calling enif_map_iterator_destroy:

ERL_NIF_TERM key, value; ErlNifMapIterator iter; enif_map_iterator_create(env, my_map, &iter, ERL_NIF_MAP_ITERATOR_FIRST); while (enif_map_iterator_get_pair(env, &iter, &key, &value)) { do_something(key,value); enif_map_iterator_next(env, &iter); } enif_map_iterator_destroy(env, &iter);

The key-value pairs of a map have no defined iteration order. The only guarantee is that the iteration order of a single map instance is preserved during the lifetime of the environment that the map belongs to.

voidenif_map_iterator_destroy(ErlNifEnv *env, ErlNifMapIterator *iter) Destroy a map iterator.

Destroys a map iterator created by enif_map_iterator_create.

intenif_map_iterator_get_pair(ErlNifEnv *env, ErlNifMapIterator *iter, ERL_NIF_TERM *key, ERL_NIF_TERM *value) Get key and value at current map iterator position.

Gets key and value terms at the current map iterator position.

On success, sets *key and *value and returns true. Returns false if the iterator is positioned at head (before first entry) or tail (beyond last entry).

intenif_map_iterator_is_head(ErlNifEnv *env, ErlNifMapIterator *iter) Check if map iterator is positioned before first.

Returns true if map iterator iter is positioned before the first entry.

intenif_map_iterator_is_tail(ErlNifEnv *env, ErlNifMapIterator *iter) Check if map iterator is positioned after last.

Returns true if map iterator iter is positioned after the last entry.

intenif_map_iterator_next(ErlNifEnv *env, ErlNifMapIterator *iter) Increment map iterator to point to next entry.

Increments map iterator to point to the next key-value entry.

Returns true if the iterator is now positioned at a valid key-value entry, or false if the iterator is positioned at the tail (beyond the last entry).

intenif_map_iterator_prev(ErlNifEnv *env, ErlNifMapIterator *iter) Decrement map iterator to point to previous entry.

Decrements map iterator to point to the previous key-value entry.

Returns true if the iterator is now positioned at a valid key-value entry, or false if the iterator is positioned at the head (before the first entry).

intenif_monitor_process(ErlNifEnv* env, void* obj, const ErlNifPid* target_pid, ErlNifMonitor* mon) Monitor a process from a resource.

Starts monitoring a process from a resource. When a process is monitored, a process exit results in a call to the provided down callback associated with the resource type.

Argument obj is pointer to the resource to hold the monitor and *target_pid identifies the local process to be monitored.

If mon is not NULL, a successful call stores the identity of the monitor in the struct pointed to by mon. This identifier is used to refer to the monitor for later removal or compare. A monitor is automatically removed when it triggers or when the resource is deallocated.

Returns 0 on success, < 0 if no down callback is provided, and > 0 if the process is no longer alive.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

ErlNifTime enif_monotonic_time(ErlNifTimeUnit time_unit) Get Erlang monotonic time.

Returns the current Erlang monotonic time. Notice that it is not uncommon with negative values.

time_unit is the time unit of the returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument, or if called from a thread that is not a scheduler thread.

See also ErlNifTime and ErlNifTimeUnit.

ErlNifMutex * enif_mutex_create(char *name)

Same as erl_drv_mutex_create.

void enif_mutex_destroy(ErlNifMutex *mtx)

Same as erl_drv_mutex_destroy.

void enif_mutex_lock(ErlNifMutex *mtx)

Same as erl_drv_mutex_lock.

int enif_mutex_trylock(ErlNifMutex *mtx)

Same as erl_drv_mutex_trylock.

void enif_mutex_unlock(ErlNifMutex *mtx)

Same as erl_drv_mutex_unlock.

ERL_NIF_TERM enif_now_time(ErlNifEnv *env)

Returns an erlang:now() time stamp.

This function is deprecated.

ErlNifResourceType * enif_open_resource_type(ErlNifEnv* env, const char* module_str, const char* name, ErlNifResourceDtor* dtor, ErlNifResourceFlags flags, ErlNifResourceFlags* tried) Create or takeover a resource type.

Creates or takes over a resource type identified by the string name and gives it the destructor function pointed to by dtor. Argument flags can have the following values:

ERL_NIF_RT_CREATE Creates a new resource type that does not already exist. ERL_NIF_RT_TAKEOVER Opens an existing resource type and takes over ownership of all its instances. The supplied destructor dtor is called both for existing instances and new instances not yet created by the calling NIF library.

The two flag values can be combined with bitwise OR. The resource type name is local to the calling module. Argument module_str is not (yet) used and must be NULL. dtor can be NULL if no destructor is needed.

On success, the function returns a pointer to the resource type and *tried is set to either ERL_NIF_RT_CREATE or ERL_NIF_RT_TAKEOVER to indicate what was done. On failure, returns NULL and sets *tried to flags. It is allowed to set tried to NULL.

Notice that enif_open_resource_type is only allowed to be called in the two callbacks load and upgrade.

ErlNifResourceType * enif_open_resource_type_x(ErlNifEnv* env, const char* name, ErlNifResourceTypeInit* init, ErlNifResourceFlags flags, ErlNifResourceFlags* tried) Create or takeover a resource type.

Same as enif_open_resource_type except is also accept a stop callback for resource types that are used together with enif_select.

Argument init is a pointer to an ErlNifResourceTypeInit structure that contains the function pointers for destructor, down and stop callbacks for the resource type.

intenif_port_command(ErlNifEnv* env, const ErlNifPort* to_port, ErlNifEnv *msg_env, ERL_NIF_TERM msg) Send a port_command to to_port.

Works as erlang:port_command/2, except that it is always completely asynchronous.

env The environment of the calling process. Must not be NULL. *to_port The port ID of the receiving port. The port ID is to refer to a port on the local node. msg_env The environment of the message term. Can be a process-independent environment allocated with enif_alloc_env or NULL. msg The message term to send. The same limitations apply as on the payload to erlang:port_command/2.

Using a msg_env of NULL is an optimization, which groups together calls to enif_alloc_env, enif_make_copy, enif_port_command, and enif_free_env into one call. This optimization is only useful when a majority of the terms are to be copied from env to msg_env.

Returns true if the command is successfully sent. Returns false if the command fails, for example:

*to_port does not refer to a local port. The currently executing process (that is, the sender) is not alive. msg is invalid.

See also enif_get_local_port.

void * enif_priv_data(ErlNifEnv* env) Get the private data of a NIF library.

Returns the pointer to the private data that was set by load or upgrade.

ERL_NIF_TERMenif_raise_exception(ErlNifEnv* env, ERL_NIF_TERM reason) Raise a NIF error exception.

Creates an error exception with the term reason to be returned from a NIF, and associates it with environment env. Once a NIF or any function it calls invokes enif_raise_exception, the runtime ensures that the exception it creates is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.

The return value from enif_raise_exception can only be used as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception, but not to any other NIF API function.

See also enif_has_pending_exception and enif_make_badarg.

int enif_realloc_binary(ErlNifBinary* bin, size_t size) Change the size of a binary.

Changes the size of a binary bin. The source binary can be read-only, in which case it is left untouched and a mutable copy is allocated and assigned to *bin.

Returns true on success, or false if memory allocation failed.

void enif_release_binary(ErlNifBinary* bin) Release a binary.

Releases a binary obtained from enif_alloc_binary.

void enif_release_resource(void* obj) Release a resource object.

Removes a reference to resource object obj obtained from enif_alloc_resource. The resource object is destructed when the last reference is removed. Each call to enif_release_resource must correspond to a previous call to enif_alloc_resource or enif_keep_resource. References made by enif_make_resource can only be removed by the garbage collector.

ErlNifRWLock * enif_rwlock_create(char *name)

Same as erl_drv_rwlock_create.

void enif_rwlock_destroy(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_destroy.

void enif_rwlock_rlock(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_rlock.

void enif_rwlock_runlock(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_runlock.

void enif_rwlock_rwlock(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_rwlock.

void enif_rwlock_rwunlock(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_rwunlock.

int enif_rwlock_tryrlock(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_tryrlock.

int enif_rwlock_tryrwlock(ErlNifRWLock *rwlck)

Same as erl_drv_rwlock_tryrwlock.

ERL_NIF_TERMenif_schedule_nif(ErlNifEnv* env, const char* fun_name, int flags, ERL_NIF_TERM (*fp)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]), int argc, const ERL_NIF_TERM argv[]) Schedule a NIF for execution.

Schedules NIF fp to execute. This function allows an application to break up long-running work into multiple regular NIF calls or to schedule a dirty NIF to execute on a dirty scheduler thread.

fun_name

Provides a name for the NIF that is scheduled for execution. If it cannot be converted to an atom, enif_schedule_nif returns a badarg exception.

flags

Must be set to 0 for a regular NIF. If the emulator was built with dirty scheduler support enabled, flags can be set to either ERL_NIF_DIRTY_JOB_CPU_BOUND if the job is expected to be CPU-bound, or ERL_NIF_DIRTY_JOB_IO_BOUND for jobs that will be I/O-bound. If dirty scheduler threads are not available in the emulator, an attempt to schedule such a job results in a badarg exception.

argc and argv

Can either be the originals passed into the calling NIF, or can be values created by the calling NIF.

The calling NIF must use the return value of enif_schedule_nif as its own return value.

Be aware that enif_schedule_nif, as its name implies, only schedules the NIF for future execution. The calling NIF does not block waiting for the scheduled NIF to execute and return. This means that the calling NIF cannot expect to receive the scheduled NIF return value and use it for further operations.

enum ErlNifSelectReturn enif_select(ErlNifEnv* env, ErlNifEvent event, enum ErlNifSelectFlags mode, void* obj, const ErlNifPid* pid, ERL_NIF_TERM ref) Manage subscription on IO event.

This function can be used to receive asynchronous notifications when OS-specific event objects become ready for either read or write operations.

Argument event identifies the event object. On Unix systems, the functions select/poll are used. The event object must be a socket, pipe or other file descriptor object that select/poll can use.

Argument mode describes the type of events to wait for. It can be ERL_NIF_SELECT_READ, ERL_NIF_SELECT_WRITE or a bitwise OR combination to wait for both. It can also be ERL_NIF_SELECT_STOP which is described further below. When a read or write event is triggerred, a notification message like this is sent to the process identified by pid:

{select, Obj, Ref, ready_input | ready_output}

ready_input or ready_output indicates if the event object is ready for reading or writing.

Argument pid may be NULL to indicate the calling process.

Argument obj is a resource object obtained from enif_alloc_resource. The purpose of the resource objects is as a container of the event object to manage its state and lifetime. A handle to the resource is received in the notification message as Obj.

Argument ref must be either a reference obtained from erlang:make_ref/0 or the atom undefined. It will be passed as Ref in the notifications. If a selective receive statement is used to wait for the notification then a reference created just before the receive will exploit a runtime optimization that bypasses all earlier received messages in the queue.

The notifications are one-shot only. To receive further notifications of the same type (read or write), repeated calls to enif_select must be made after receiving each notification.

Use ERL_NIF_SELECT_STOP as mode in order to safely close an event object that has been passed to enif_select. The stop callback of the resource obj will be called when it is safe to close the event object. This safe way of closing event objects must be used even if all notifications have been received and no further calls to enif_select have been made.

Returns an integer where different bits indicate the outcome of the call:

ERL_NIF_SELECT_ERROR The master error bit. It will always be set if the call failed for any reason. ERL_NIF_SELECT_STOP_CALLED The stop callback was called directly by enif_select. ERL_NIF_SELECT_STOP_SCHEDULED The stop callback was scheduled to run on some other thread or later by this thread. ERL_NIF_SELECT_INVALID_EVENT Argument event is not a valid OS event object. ERL_NIF_SELECT_FAILED The system call failed to add the event object to the poll set.

The return value from a successful call with mode as ERL_NIF_SELECT_STOP, will contain either bit ERL_NIF_SELECT_STOP_CALLED or ERL_NIF_SELECT_STOP_SCHEDULED.

Always use bitwise AND to test the return value. New significant bits may be added in future releases to give more detailed information for both failed and successful calls. Do NOT use equallity tests like ==, as that may cause your application to stop working.

Example:

retval = enif_select(env, fd, ERL_NIF_SELECT_READ, resource, ref); if (retval & ERL_NIF_SELECT_ERROR) { /* handle error */ } /* Success! */
ErlNifPid * enif_self(ErlNifEnv* caller_env, ErlNifPid* pid) Get the pid of the calling process.

Initializes the pid variable *pid to represent the calling process.

Returns pid.

intenif_send(ErlNifEnv* env, ErlNifPid* to_pid, ErlNifEnv* msg_env, ERL_NIF_TERM msg) Send a message to a process.

Sends a message to a process.

env The environment of the calling process. Must be NULL only if calling from a created thread. *to_pid The pid of the receiving process. The pid is to refer to a process on the local node. msg_env The environment of the message term. Must be a process-independent environment allocated with enif_alloc_env or NULL. msg The message term to send.

Returns true if the message is successfully sent. Returns false if the send operation fails, that is:

*to_pid does not refer to an alive local process. The currently executing process (that is, the sender) is not alive.

The message environment msg_env with all its terms (including msg) is invalidated by a successful call to enif_send. The environment is to either be freed with enif_free_env of cleared for reuse with enif_clear_env.

If msg_env is set to NULL, the msg term is copied and the original term and its environemt is still valid after the call.

This function is only thread-safe when the emulator with SMP support is used. It can only be used in a non-SMP emulator from a NIF-calling thread.

Passing msg_env as NULL is only supported as from ERTS 8.0 (Erlang/OTP 19).

unsigned enif_sizeof_resource(void* obj) Get the byte size of a resource object.

Gets the byte size of resource object obj obtained by enif_alloc_resource.

intenif_snprintf(char *str, size_t size, const char *format, ...) Format strings and Erlang terms.

Similar to snprintf but this format string also accepts "%T", which formats Erlang terms.

voidenif_system_info(ErlNifSysInfo *sys_info_ptr, size_t size) Get information about the Erlang runtime system.

Same as driver_system_info.

intenif_term_to_binary(ErlNifEnv *env, ERL_NIF_TERM term, ErlNifBinary *bin) Convert a term to the external format.

Allocates a new binary with enif_alloc_binary and stores the result of encoding term according to the Erlang external term format.

Returns true on success, or false if the allocation fails.

See also erlang:term_to_binary/1 and enif_binary_to_term.

int enif_thread_create(char *name,ErlNifTid *tid,void * (*func)(void *),void *args,ErlNifThreadOpts *opts)

Same as erl_drv_thread_create.

void enif_thread_exit(void *resp)

Same as erl_drv_thread_exit.

int enif_thread_join(ErlNifTid, void **respp)

Same as erl_drv_thread_join.

ErlNifThreadOpts * enif_thread_opts_create(char *name)

Same as erl_drv_thread_opts_create.

void enif_thread_opts_destroy(ErlNifThreadOpts *opts)

Same as erl_drv_thread_opts_destroy.

ErlNifTid enif_thread_self(void)

Same as erl_drv_thread_self.

int enif_thread_type(void) Determine type of current thread

Determine the type of currently executing thread. A positive value indicates a scheduler thread while a negative value or zero indicates another type of thread. Currently the following specific types exist (which may be extended in the future):

ERL_NIF_THR_UNDEFINED

Undefined thread that is not a scheduler thread.

ERL_NIF_THR_NORMAL_SCHEDULER

A normal scheduler thread.

ERL_NIF_THR_DIRTY_CPU_SCHEDULER

A dirty CPU scheduler thread.

ERL_NIF_THR_DIRTY_IO_SCHEDULER

A dirty I/O scheduler thread.

ErlNifTime enif_time_offset(ErlNifTimeUnit time_unit) Get current time offset.

Returns the current time offset between Erlang monotonic time and Erlang system time converted into the time_unit passed as argument.

time_unit is the time unit of the returned value.

Returns ERL_NIF_TIME_ERROR if called with an invalid time unit argument or if called from a thread that is not a scheduler thread.

See also ErlNifTime and ErlNifTimeUnit.

void * enif_tsd_get(ErlNifTSDKey key)

Same as erl_drv_tsd_get.

int enif_tsd_key_create(char *name, ErlNifTSDKey *key)

Same as erl_drv_tsd_key_create.

void enif_tsd_key_destroy(ErlNifTSDKey key)

Same as erl_drv_tsd_key_destroy.

void enif_tsd_set(ErlNifTSDKey key, void *data)

Same as erl_drv_tsd_set.

See Also

erlang:load_nif/2