diff options
Diffstat (limited to 'erts/doc/src/erl_nif.xml')
| -rw-r--r-- | erts/doc/src/erl_nif.xml | 123 |
1 files changed, 81 insertions, 42 deletions
diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml index 5fc6508aad..f00f7b9f46 100644 --- a/erts/doc/src/erl_nif.xml +++ b/erts/doc/src/erl_nif.xml @@ -4,7 +4,7 @@ <cref> <header> <copyright> - <year>2001</year><year>2011</year> + <year>2001</year><year>2012</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -34,30 +34,6 @@ <lib>erl_nif</lib> <libsummary>API functions for an Erlang NIF library</libsummary> <description> - <note><p>The NIF concept is officially supported from R14B. NIF source code - written for earlier experimental versions might need adaption to run on R14B.</p> - <p>No incompatible changes between <em>R14B</em> and R14A.</p> - <p>Incompatible changes between <em>R14A</em> and R13B04:</p> - <list> - <item>Environment argument removed for <c>enif_alloc</c>, - <c>enif_realloc</c>, <c>enif_free</c>, <c>enif_alloc_binary</c>, - <c>enif_realloc_binary</c>, <c>enif_release_binary</c>, - <c>enif_alloc_resource</c>, <c>enif_release_resource</c>, - <c>enif_is_identical</c> and <c>enif_compare</c>.</item> - <item>Character encoding argument added to <c>enif_get_atom</c> - and <c>enif_make_existing_atom</c>.</item> - <item>Module argument added to <c>enif_open_resource_type</c> - while changing name spaces of resource types from global to module local.</item> - </list> - <p>Incompatible changes between <em>R13B04</em> and R13B03:</p> - <list> - <item>The function prototypes of the NIFs have changed to expect <c>argc</c> and <c>argv</c> - arguments. The arity of a NIF is by that no longer limited to 3.</item> - <item><c>enif_get_data</c> renamed as <c>enif_priv_data</c>.</item> - <item><c>enif_make_string</c> got a third argument for character encoding.</item> - </list> - </note> - <p>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 @@ -67,6 +43,57 @@ 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.</p> + <marker id="WARNING"/> + <warning><p><em>Use this functionality with extreme care!</em></p> + <p>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 can <em>not</em> provide the same services as provided when + executing Erlang code, such as preemptive scheduling or memory + protection. If the native function doesn't behave well, the whole + VM will misbehave.</p> + <list> + <item><p>A native function that crash will crash the whole VM.</p></item> + <item><p>An erroneously implemented native function might cause + a VM internal state inconsistency which may cause a crash of the VM, + or miscellaneous misbehaviors of the VM at any point after the call + to the native function.</p></item> + <item><p>A native function that do <seealso marker="#lengthy_work">lengthy + work</seealso> before returning will degrade responsiveness of the VM, + and may 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 might occur due + to lengthy work may also vary between OTP releases.</p></item> + </list> + </warning> + + <p>The NIF concept is officially supported from R14B. NIF source code + written for earlier experimental versions might need adaption to run on R14B + or later versions:</p> + <list> + <item>No incompatible changes between <em>R14B</em> and R14A.</item> + <item>Incompatible changes between <em>R14A</em> and R13B04: + <list> + <item>Environment argument removed for <c>enif_alloc</c>, + <c>enif_realloc</c>, <c>enif_free</c>, <c>enif_alloc_binary</c>, + <c>enif_realloc_binary</c>, <c>enif_release_binary</c>, + <c>enif_alloc_resource</c>, <c>enif_release_resource</c>, + <c>enif_is_identical</c> and <c>enif_compare</c>.</item> + <item>Character encoding argument added to <c>enif_get_atom</c> + and <c>enif_make_existing_atom</c>.</item> + <item>Module argument added to <c>enif_open_resource_type</c> + while changing name spaces of resource types from global to module local.</item> + </list> + </item> + <item>Incompatible changes between <em>R13B04</em> and R13B03: + <list> + <item>The function prototypes of the NIFs have changed to expect <c>argc</c> and <c>argv</c> + arguments. The arity of a NIF is by that no longer limited to 3.</item> + <item><c>enif_get_data</c> renamed as <c>enif_priv_data</c>.</item> + <item><c>enif_make_string</c> got a third argument for character encoding.</item> + </list> + </item> + </list> + <p>A minimal example of a NIF library can look like this:</p> <p/> <code type="none"> @@ -136,7 +163,23 @@ ok then retrieved by calling <seealso marker="#enif_priv_data">enif_priv_data</seealso>.</p> <p>There is no way to explicitly unload a NIF library. A library will be automatically unloaded when the module code that it belongs to is purged - by the code server.</p> + by the code server.</p> + + <p><marker id="lengthy_work"/> + As mentioned in the <seealso marker="#WARNING">warning</seealso> text at + the beginning of this document it is of vital importance that a native function + does return relatively fast. It is hard to give an exact maximum amount + of time that a native function is allowed to work, but as a rule of thumb + a well behaving native function should return to its caller before a + millisecond has passed. This can be achieved using different approaches. + If you have full control over the code that are 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 might, however, + not always be possible, e.g. when calling third party libraries. In this + case you typically want to dispatch the work to another thread, return + from the native function, and wait for the result. The thread can send + the result back to the calling thread using message passing. Information + about thread primitives can be found below.</p> </description> <section> <title>FUNCTIONALITY</title> @@ -266,10 +309,6 @@ ok mutable.</p> <p>The library initialization callbacks <c>load</c>, <c>reload</c> and <c>upgrade</c> are all thread-safe even for shared state data.</p> - <p>Avoid doing lengthy work in NIF calls as that may degrade the - responsiveness of the VM. NIFs are called directly by the same scheduler - thread that executed the calling Erlang code. The calling scheduler will thus - be blocked from doing any other work until the NIF returns.</p> </item> </taglist> </section> @@ -472,7 +511,7 @@ typedef enum { </section> <funcs> - <func><name><ret>void*</ret><nametext>enif_alloc(size_t size)</nametext></name> + <func><name><ret>void *</ret><nametext>enif_alloc(size_t size)</nametext></name> <fsummary>Allocate dynamic memory.</fsummary> <desc><p>Allocate memory of <c>size</c> bytes. Return NULL if allocation failed.</p></desc> </func> @@ -489,7 +528,7 @@ typedef enum { <p>Return true on success or false if allocation failed.</p> </desc> </func> - <func><name><ret>ErlNifEnv*</ret><nametext>enif_alloc_env()</nametext></name> + <func><name><ret>ErlNifEnv *</ret><nametext>enif_alloc_env()</nametext></name> <fsummary>Create a new environment</fsummary> <desc><p>Allocate a new process independent environment. The environment can be used to hold terms that is not bound to any process. Such terms can @@ -499,7 +538,7 @@ typedef enum { <p>Return pointer to the new environment.</p> </desc> </func> - <func><name><ret>void*</ret><nametext>enif_alloc_resource(ErlNifResourceType* type, unsigned size)</nametext></name> + <func><name><ret>void *</ret><nametext>enif_alloc_resource(ErlNifResourceType* type, unsigned size)</nametext></name> <fsummary>Allocate a memory managed resource object</fsummary> <desc><p>Allocate a memory managed resource object of type <c>type</c> and size <c>size</c> bytes.</p></desc> </func> @@ -522,7 +561,7 @@ typedef enum { <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_broadcast">erl_drv_cond_broadcast</seealso>. </p></desc> </func> - <func><name><ret>ErlNifCond*</ret><nametext>enif_cond_create(char *name)</nametext></name> + <func><name><ret>ErlNifCond *</ret><nametext>enif_cond_create(char *name)</nametext></name> <fsummary></fsummary> <desc><p>Same as <seealso marker="erl_driver#erl_drv_cond_create">erl_drv_cond_create</seealso>. </p></desc> @@ -840,7 +879,7 @@ typedef enum { <fsummary>Create an integer term from a long int</fsummary> <desc><p>Create an integer term from a <c>long int</c>.</p></desc> </func> - <func><name><ret>unsigned char*</ret><nametext>enif_make_new_binary(ErlNifEnv* env, size_t size, ERL_NIF_TERM* termp)</nametext></name> + <func><name><ret>unsigned char *</ret><nametext>enif_make_new_binary(ErlNifEnv* env, size_t size, ERL_NIF_TERM* termp)</nametext></name> <fsummary>Allocate and create a new binary term</fsummary> <desc><p>Allocate a binary of size <c>size</c> bytes and create an owning term. The binary data is mutable until the calling NIF returns. This is a @@ -951,7 +990,7 @@ typedef enum { <fsummary>Create an integer term from an unsigned long int</fsummary> <desc><p>Create an integer term from an <c>unsigned long int</c>.</p></desc> </func> - <func><name><ret>ErlNifMutex*</ret><nametext>enif_mutex_create(char *name)</nametext></name> + <func><name><ret>ErlNifMutex *</ret><nametext>enif_mutex_create(char *name)</nametext></name> <fsummary></fsummary> <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_create">erl_drv_mutex_create</seealso>. </p></desc> @@ -976,7 +1015,7 @@ typedef enum { <desc><p>Same as <seealso marker="erl_driver#erl_drv_mutex_unlock">erl_drv_mutex_unlock</seealso>. </p></desc> </func> - <func><name><ret>ErlNifResourceType*</ret><nametext>enif_open_resource_type(ErlNifEnv* env, + <func><name><ret>ErlNifResourceType *</ret><nametext>enif_open_resource_type(ErlNifEnv* env, const char* module_str, const char* name, ErlNifResourceDtor* dtor, ErlNifResourceFlags flags, ErlNifResourceFlags* tried)</nametext></name> <fsummary>Create or takeover a resource type</fsummary> @@ -1005,7 +1044,7 @@ typedef enum { and <seealso marker="#upgrade">upgrade</seealso>.</p> </desc> </func> - <func><name><ret>void*</ret><nametext>enif_priv_data(ErlNifEnv* env)</nametext></name> + <func><name><ret>void *</ret><nametext>enif_priv_data(ErlNifEnv* env)</nametext></name> <fsummary>Get the private data of a NIF library</fsummary> <desc><p>Return the pointer to the private data that was set by <c>load</c>, <c>reload</c> or <c>upgrade</c>.</p> @@ -1033,7 +1072,7 @@ typedef enum { References made by <seealso marker="#enif_make_resource">enif_make_resource</seealso> can only be removed by the garbage collector.</p></desc> </func> - <func><name><ret>ErlNifRWLock*</ret><nametext>enif_rwlock_create(char *name)</nametext></name> + <func><name><ret>ErlNifRWLock *</ret><nametext>enif_rwlock_create(char *name)</nametext></name> <fsummary></fsummary> <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_create">erl_drv_rwlock_create</seealso>. </p></desc> @@ -1073,7 +1112,7 @@ typedef enum { <desc><p>Same as <seealso marker="erl_driver#erl_drv_rwlock_tryrwlock">erl_drv_rwlock_tryrwlock</seealso>. </p></desc> </func> - <func><name><ret>ErlNifPid*</ret><nametext>enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)</nametext></name> + <func><name><ret>ErlNifPid *</ret><nametext>enif_self(ErlNifEnv* caller_env, ErlNifPid* pid)</nametext></name> <fsummary>Get the pid of the calling process.</fsummary> <desc><p>Initialize the pid variable <c>*pid</c> to represent the calling process. Return <c>pid</c>.</p></desc> @@ -1129,7 +1168,7 @@ typedef enum { <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_join">erl_drv_thread_join </seealso>. </p></desc> </func> - <func><name><ret>ErlNifThreadOpts*</ret><nametext>enif_thread_opts_create(char *name)</nametext></name> + <func><name><ret>ErlNifThreadOpts *</ret><nametext>enif_thread_opts_create(char *name)</nametext></name> <fsummary></fsummary> <desc><p>Same as <seealso marker="erl_driver#erl_drv_thread_opts_create">erl_drv_thread_opts_create</seealso>. </p></desc> @@ -1154,7 +1193,7 @@ typedef enum { <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_key_destroy">erl_drv_tsd_key_destroy</seealso>. </p></desc> </func> - <func><name><ret>void*</ret><nametext>enif_tsd_get(ErlNifTSDKey key)</nametext></name> + <func><name><ret>void *</ret><nametext>enif_tsd_get(ErlNifTSDKey key)</nametext></name> <fsummary></fsummary> <desc><p>Same as <seealso marker="erl_driver#erl_drv_tsd_get">erl_drv_tsd_get</seealso>. </p></desc> |