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Persistent terms are useful for storing Erlang terms that are never
or infrequently updated. They have the following advantages:
* Constant time access. A persistent term is not copied when it is
looked up. The constant factor is lower than for ETS, and no locks
are taken when looking up a term.
* Persistent terms are not copied in garbage collections.
* There is only ever one copy of a persistent term (until it is
deleted). That makes them useful for storing configuration data
that needs to be easily accessible by all processes.
Persistent terms have the following drawbacks:
* Updates are expensive. The hash table holding the keys for the
persistent terms are updated whenever a persistent term is added,
updated or deleted.
* Updating or deleting a persistent term triggers a "global GC", which
will schedule a heap scan of all processes to search the heap of all
processes for the deleted term. If a process still holds a reference
to the deleted term, the process will be garbage collected and the
term copied to the heap of the process. This global GC can make the
system less responsive for some time.
Three BIFs (implemented in C in the emulator) is the entire
interface to the persistent term functionality:
* put(Key, Value) to store a persistent term.
* get(Key) to look up a persistent term.
* erase(Key) to delete a persistent term.
There are also two additional BIFs to obtain information about
persistent terms:
* info() to return a map with information about persistent terms.
* get() to return a list of a {Key,Value} tuples for all persistent
terms. (The values are not copied.)
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This commit replaces the old memory instrumentation with a new
implementation that scans carriers instead of wrapping
erts_alloc/erts_free. The old implementation could not extract
information without halting the emulator, had considerable runtime
overhead, and the memory maps it produced were noisy and lacked
critical information.
Since the new implementation walks through existing data structures
there's no longer a need to start the emulator with special flags to
get information about carrier utilization/fragmentation. Memory
fragmentation is also easier to diagnose as it's presented on a
per-carrier basis which eliminates the need to account for "holes"
between mmap segments.
To help track allocations, each allocation can now be tagged with
what it is and who allocated it at the cost of one extra word per
allocation. This is controlled on a per-allocator basis with the
+M<S>atags option, and is enabled by default for binary_alloc and
driver_alloc (which is also used by NIFs).
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* rickard/signals/OTP-14589:
Fix VM probes compilation
Fix lock counting
Fix signal order for is_process_alive
Fix signal handling priority elevation
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* bjorn/erts/eliminate-get_stacktrace:
Eliminate use of erlang:get_stacktrace/0 in preloaded modules
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Communication between Erlang processes has conceptually always been
performed through asynchronous signaling. The runtime system
implementation has however previously preformed most operation
synchronously. In a system with only one true thread of execution, this
is not problematic (often the opposite). In a system with multiple threads
of execution (as current runtime system implementation with SMP support)
it becomes problematic. This since it often involves locking of structures
when updating them which in turn cause resource contention. Utilizing
true asynchronous communication often avoids these resource contention
issues.
The case that triggered this change was contention on the link lock due
to frequent updates of the monitor trees during communication with a
frequently used server. The signal order delivery guarantees of the
language makes it hard to change the implementation of only some signals
to use true asynchronous signaling. Therefore the implementations
of (almost) all signals have been changed.
Currently the following signals have been implemented as true
asynchronous signals:
- Message signals
- Exit signals
- Monitor signals
- Demonitor signals
- Monitor triggered signals (DOWN, CHANGE, etc)
- Link signals
- Unlink signals
- Group leader signals
All of the above already defined as asynchronous signals in the
language. The implementation of messages signals was quite
asynchronous to begin with, but had quite strict delivery constraints
due to the ordering guarantees of signals between a pair of processes.
The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts
that service all kinds of signals. More details regarding the signal
queue can be found in comments in the erl_proc_sig_queue.h file.
The monitor and link implementations have also been completely replaced
in order to fit the new asynchronous signaling implementation as good
as possible. More details regarding the new monitor and link
implementations can be found in the erl_monitor_link.h file.
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to replace DFLAGS_STRICT_ORDER_DELIVERY
and remove that compile time dependency.
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for kernel to ask erts about distribution flags
and keep this info in one place.
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* lukas/stdlib/maps_iterators/OTP-14012:
erts: Limit size of first iterator for hashmaps
Update primary bootstrap
Update preloaded modules
erts: Remove erts_internal:maps_to_list/2
stdlib: Make io_lib and io_lib_pretty use maps iterator
erts: Implement batching maps:iterator
erts: Implement maps path iterator
erts: Implement map iterator using a stack
stdlib: Introduce maps iterator API
Conflicts:
bootstrap/lib/stdlib/ebin/io_lib.beam
bootstrap/lib/stdlib/ebin/io_lib_pretty.beam
erts/emulator/beam/bif.tab
erts/preloaded/ebin/erlang.beam
erts/preloaded/ebin/erts_internal.beam
erts/preloaded/ebin/zlib.beam
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This function is no longer needed as maps:iterator has
now been implemented.
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This iterator implementation fetches multiple elements to
iterate over in one call to erts_internal:maps_next instead
of one at a time. This means that the memory usage will go
up for the iterator as we are buffering elements, but the
usage is still bounded.
In this implementation the max memory usage is 1000 words.
Using this approach makes the iterator as fast as using
maps:to_list, so maps:iterator/2 has been removed.
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and drop _id suffix.
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* maint:
Update preloaded
erts: Correct type declaration of match specification head
Conflicts:
erts/preloaded/ebin/erlang.beam
erts/preloaded/ebin/erts_internal.beam
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Bug reported by Peti Gömöri <[email protected]>.
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* maint:
erts: Add nif_SUITE:t_on_load
erts: Improve nif_SUITE:upgrade test
Don't leak old code when loading a modules with an on_load function
Conflicts:
erts/preloaded/ebin/erts_code_purger.beam
erts/preloaded/ebin/erts_internal.beam
erts/preloaded/src/erts_code_purger.erl
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Normally, calling code:delete/1 before re-loading the code for a
module is unnecessary but causes no problem.
But there will be be problems if the new code has an on_load function.
Code with an on_load function will always be loaded as old code
to allowed it to be easily purged if the on_load function would fail.
If the on_load function succeeds, the old and current code will be
swapped.
So in the scenario where code:delete/1 has been called explicitly,
there is old code but no current code. Loading code with an
on_load function will cause the reference to the old code to be
overwritten. That will at best cause a memory leak, and at worst
an emulator crash (especially if NIFs are involved).
To avoid that situation, we will put the code with the on_load
function in a special, third slot in Module.
ERL-240
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* kvakvs/erts/gc_minor_option/OTP-11695:
erts: Fix req_system_task gc typespec
Fix process_SUITE system_task_blast and no_priority_inversion2
Option to erlang:garbage_collect to request minor (generational) GC
Conflicts:
erts/emulator/beam/erl_process.c
erts/preloaded/src/erts_internal.erl
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Ensure that we cannot get any dangling pointers into code that
has been purged. This is done by a two phase purge. At first
phase all fun entries pointing into the code to purge are marked
for purge. All processes trying to call these funs will be suspended
and by this we avoid getting new direct references into the code.
When all processes has been checked, these processes are resumed.
The new purge strategy now also completely ignore the existence of
indirect references to the code (funs). If such exist, they will
cause bad fun exceptions to the caller, but will not prevent a
soft purge or cause a kill of a process having such live references
during a hard purge. This since it is impossible to give any
guarantees that no processes in the system have such indirect
references. Even when the system is completely clean from such
references, new ones can appear via distribution and/or disk.
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Note: Minor GC option is a hint, and GC may still decide to run fullsweep.
Test case for major and minor gc on self
Test case for major and minor gs on some other process + async gc test check
docs fix
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Add the possibility to use modules as trace data receivers. The functions
in the module have to be nifs as otherwise complex trace probes will be
very hard to handle (complex means trace probes for ports for example).
This commit changes the way that the ptab->tracer field works from always
being an immediate, to now be NIL if no tracer is present or else be
the tuple {TracerModule, TracerState} where TracerModule is an atom that
is later used to lookup the appropriate tracer callbacks to call and
TracerState is just passed to the tracer callback. The default process and
port tracers have been rewritten to use the new API.
This commit also changes the order which trace messages are delivered to the
potential tracer process. Any enif_send done in a tracer module may be delayed
indefinitely because of lock order issues. If a message is delayed any other
trace message send from that process is also delayed so that order is preserved
for each traced entity. This means that for some trace events (i.e. send/receive)
the events may come in an unintuitive order (receive before send) to the
trace receiver. Timestamps are taken when the trace message is generated so
trace messages from differented processes may arrive with the timestamp
out of order.
Both the erlang:trace and seq_trace:set_system_tracer accept the new tracer
module tracers and also the backwards compatible arguments.
OTP-10267
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Conflicts:
erts/emulator/beam/erl_alloc.types
erts/emulator/beam/erl_bif_info.c
erts/emulator/beam/erl_process.c
erts/preloaded/ebin/erts_internal.beam
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This commit implements erts_internal:system_check(schedulers) with the
intent of a basic responsiveness test check of the schedulers.
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* sverk/safe-purging/OTP-13122:
erts: Fix harmless dialyzer warnings
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Microstate accounting is a way to track which state the
different threads within ERTS are in. The main usage area
is to pin point performance bottlenecks by checking which
states the threads are in and then from there figuring out
why and where to optimize.
Since checking whether microstate accounting is on or off is
relatively expensive if done in a short loop only a few of the
states are enabled by default and more states can be enabled
through configure.
I've done some benchmarking and the overhead with it turned off
is not noticible and with it on it is a fraction of a percent.
If you enable the extra states, depending on the benchmark,
the ovehead when turned off is about 1% and when turned on
somewhere inbetween 5-15%.
OTP-12345
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The perf_counter is a very very cheap and high resolution timer
that can be used to timestamp system events. It does not have
monoticity guarantees, but should on most OS's expose a monotonous
time.
A special instruction has been created for this counter to further
speed up fetching it.
OTP-12908
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by ignoring literals.
erts_internal:check_process_code will be called again anyway
(with option {copy_literals, true}) before the module is actually purged.
No need to check literals twice.
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Move impl from erlang to erts_internal. Cut and paste.
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as it's not a public interface.
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Problem: erlang:purge_module/1 is not safe in the sense
that very bad things may happen if the code to be purged
is still referred to by live processes.
Introduce erts_internal:purge_module which is the same as the old
erlang:purge_module BIF (except it returns false if no such old module).
Implement erlang:purge_module in Erlang and let it invoke
erts_code_purger for safe purging where all clogging processes
first are killed.
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* lukas/erts/forker: (28 commits)
erts: Never abort in the forked child
erts: Mend ASSERT makro for erl_child_setup
erts: Allow enomem failures in port_SUITE
erts: iter_port sleep longer on freebsd
erts: Allow one dangling fd if there is a gethost port
erts: Only use forker StackAck on freebsd
erts: It is not possible to exit the forker driver
erts: Add forker StartAck for port start flowcontrol
erts: Fix large open_port arg segfault for win32
erts: Fix memory leak at async open port
kernel: Remove cmd server for unix os:cmd
erts: Add testcase for huge port environment
erts: Move os_pid to port hash to child setup
erts: Handle all EINTR and EAGAIN cases in child setup
erts: Make child_setup work with large environments
erts: Fix forker driver ifdefs for win32
erts: Fix uds socket handling for os x
erts: Fix dereferencing of unaligned integer for sparc
erts: Flatten too long io vectors in uds write
erts: Add fd count test for spawn_driver
...
Conflicts:
erts/emulator/beam/erl_node_tables.c
erts/preloaded/src/erts_internal.erl
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OTP-13086
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