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The dist messages EXIT, EXIT2 and MONITOR_DOWN have been
updated with new versions that send the reason term as
part of the payload of the message instead of as part
of the control message.
This allows the decode of the reason to be done by the
receiving process instead of the dist entry which in turn
makes it possible for multiple decodes to be done in
parallel.
This change is done in order to make it easier to fragment
the potentially large payload of EXIT, EXIT2 and MONITOR_DOWN
into multiple distribution messages.
OTP-15611
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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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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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Consider the following function:
function({function,Name,Arity,CLabel,Is0}, Lc0) ->
try
%% Optimize the code for the function.
catch
Class:Error:Stack ->
io:format("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
end.
The stacktrace is retrieved, but it is only used in the call
to erlang:raise/3. There is no need to build a stacktrace
in this function. We can avoid the building if we introduce
an instruction called raw_raise/3 that works exactly like
the erlang:raise/3 BIF except that its third argument must
be a raw stacktrace.
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by preventing it from doing GC, which generated code relies on.
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HiPE: Support for literal tag, tests and bugfixes
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which was replaced by 'is_unicode' in 5369e34a892bfd8ab5aa98df330e3bbf19497b71
but kept for ABI compatibility in OTP-20.*.
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Since gcunsafe values are live over is_divisible calls (although only
the happy path, which never GCd), it should be a primop so there cannot
be any GCs.
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by introducing new primop 'is_unicode'
with no exception (ab)use and no GC.
Replaces bs_validate_unicode which is kept for backward compat for now.
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This refactor was done using the unifdef tool like this:
for file in $(find erts/ -name *.[ch]); do unifdef -t -f defile -o $file $file; done
where defile contained:
#define ERTS_SMP 1
#define USE_THREADS 1
#define DDLL_SMP 1
#define ERTS_HAVE_SMP_EMU 1
#define SMP 1
#define ERL_BITS_REENTRANT 1
#define ERTS_USE_ASYNC_READY_Q 1
#define FDBLOCK 1
#undef ERTS_POLL_NEED_ASYNC_INTERRUPT_SUPPORT
#define ERTS_POLL_ASYNC_INTERRUPT_SUPPORT 0
#define ERTS_POLL_USE_WAKEUP_PIPE 1
#define ERTS_POLL_USE_UPDATE_REQUESTS_QUEUE 1
#undef ERTS_HAVE_PLAIN_EMU
#undef ERTS_SIGNAL_STATE
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Only term_to_binary needed some extra attention
as it used to initialize refc as 0 instead of 1.
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* maint:
Atomic reference count of binaries also in non-SMP
Conflicts:
erts/emulator/beam/erl_fun.c
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OTP-14202
* rickard/binary-refc:
Atomic reference count of binaries also in non-SMP
Conflicts:
erts/emulator/beam/beam_bp.c
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NIF resources was not handled in a thread-safe manner in the runtime
system without SMP support.
As a consequence of this fix, the following driver functions are now
thread-safe also in the runtime system without SMP support:
- driver_free_binary()
- driver_realloc_binary()
- driver_binary_get_refc()
- driver_binary_inc_refc()
- driver_binary_dec_refc()
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* maint:
Remove debug printout and unnecessary GC
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All 'EXIT' and monitor messages are sent from 'system'
Timeouts are "sent" from 'clock_service'
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This is mostly a pure refactoring.
Except for the buggy cases when calling erlang:halt() with a positive
integer in the range -(INT_MIN+2) to -INT_MIN that got confused with
ERTS_ABORT_EXIT, ERTS_DUMP_EXIT and ERTS_INTR_EXIT.
Outcome OLD erl_exit(n, ) NEW erts_exit(n, )
------- ------------------- -------------------------------------------
exit(Status) n = -Status <= 0 n = Status >= 0
crashdump+abort n > 0, ignore n n = ERTS_ERROR_EXIT < 0
The outcome of the old ERTS_ABORT_EXIT, ERTS_INTR_EXIT and
ERTS_DUMP_EXIT are the same as before (even though their values have
changed).
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Conflicts:
erts/emulator/beam/beam_emu.c
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Processes remember heap fragments that are known to be fully
live due to creation in a just called BIF that yields in the
live_hf_end field. This field must not be used if we have not
disabled GC in a BIF. F_DELAY_GC has been introduced in order
to distinguish between to two different scenarios.
- F_DISABLE_GC should *only* be used by BIFs. This when
the BIF needs to yield while preventig a GC.
- F_DELAY_GC should only be used when GC is temporarily
disabled while the process is scheduled. A process must
not be scheduled out while F_DELAY_GC is set.
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This feature was previously missing and expressions such as
<<<<1:1>>/binary>> would succeed construction when compiled with HiPE.
A primop is_divisible is introduced to handle the case when the unit
size is not a power of two.
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* rickard/gc-bump-reds/OTP-13097:
Bump reductions on GC
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* rickard/ohmq/OTP-13047:
Fragmented young heap generation and off_heap_message_queue option
Refactor GC
Introduce literal tag
Conflicts:
erts/doc/src/erlang.xml
erts/emulator/beam/erl_gc.c
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* The youngest generation of the heap can now consist of multiple
blocks. Heap fragments and message fragments are added to the
youngest generation when needed without triggering a GC. After
a GC the youngest generation is contained in one single block.
* The off_heap_message_queue process flag has been added. When
enabled all message data in the queue is kept off heap. When
a message is selected from the queue, the message fragment (or
heap fragment) containing the actual message is attached to the
youngest generation. Messages stored off heap is not part of GC.
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These ifdef-ed lines were once upon a time needed, but the recent
changes in the time mechanism of OTP render them unused and result
in a warning on architectures which are not 64-bit.
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except the reference counter 'refc', as different callers
have different strategies regarding the lifetime of the binary.
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A process requesting a system task to be executed in the context of
another process will be notified by a message when the task has
executed. This message will be on the form:
{RequestType, RequestId, Pid, Result}.
A process requesting a system task to be executed can set priority
on the system task. The requester typically set the same priority
on the task as its own process priority, and by this avoiding
priority inversion. A request for execution of a system task is
made by calling the statically linked in NIF
erts_internal:request_system_task(Pid, Prio, Request). This is an
undocumented ERTS internal function that should remain so. It
should *only* be called from BIF implementations.
Currently defined system tasks are:
* garbage_collect
* check_process_code
Further system tasks can and will be implemented in the future.
The erlang:garbage_collect/[1,2] and erlang:check_process_code/[2,3]
BIFs are now implemented using system tasks. Both the
'garbage_collect' and the 'check_process_code' operations perform
or may perform garbage_collections. By doing these via the
system task functionality all garbage collect operations in the
system will be performed solely in the context of the process
being garbage collected. This makes it possible to later implement
functionality for disabling garbage collection of a process over
context switches.
Newly introduced BIFs:
* erlang:garbage_collect/2 - The new second argument is an option
list. Introduced option:
* {async, RequestId} - making it possible for users to issue
asynchronous garbage collect requests.
* erlang:check_process_code/3 - The new third argument is an
option list. Introduced options:
* {async, RequestId} - making it possible for users to issue
asynchronous check process code requests.
* {allow_gc, boolean()} - making it possible to issue requests
that aren't allowed to garbage collect (operation will abort
if gc should be needed).
These options have been introduced as a preparation for
parallelization of check_process_code operations when the
code_server is about to purge a module.
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These primops use the standard_bif_interface_X macros in
hipe_bif_list.m4 and must therefor be implemented as bifs for things to work.
Maybe there is room for optimization here to call the primops more directly
with arguments in registers without having to push them on stack to emulate
bif calls.
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A first step to adapt hipe to the new BIF calling convention.
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All uses of the old deprecated atomic API in the runtime system
have been replaced with the use of the new atomic API. In a lot of
places this change imply a relaxation of memory barriers used.
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