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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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Floating point exceptions has been disabled since 2011 on macOS
(fa0f8d2c29b) and on Linux since 2014 (c7ddafbe6dbc) because
there were unresolved stability issues.
Floating point exceptions are not disabled by default on FreeBSD,
and if OTP is compiled with gcc (as opposed to clang) floating
point exceptions will be used.
81a6adab693a introduced a bug in erts/emulator/Makefile.in which would
cause the building of OTP to fail if floating point exceptions were
enabled. The bug was not noticed because it turns out that none of our
daily build machines has floating point exceptions enabled.
Since floating point exceptions is not tested, we should not expect
them to work reliably on any platform. Therefore, turn off floating
point exceptions unconditionally in erts/configure.in. For the moment
we will keep the code in the runtime system that handles floating
point exceptions.
(This commit also fixes the bug in erts/emulator/Makefile.in, in
case floating point exceptions ever become reliable and enabled.)
https://bugs.erlang.org/browse/ERL-620
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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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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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putenv(3) and friends aren't thread-safe regardless of how you slice
it; a global lock around all environment operations (like before)
keeps things safe as far as our own operations go, but we have
absolutely no control over what libc or a library dragged in by a
driver/NIF does -- they're free to call getenv(3) or putenv(3)
without honoring our lock.
This commit solves this by setting up an "emulated" environment which
can't be touched without going through our interfaces. Third-party
libraries can still shoot themselves in the foot but benign uses of
os:putenv/2 will no longer risk crashing the emulator.
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This improves the latency of file operations as dirty schedulers
are a bit more eager to run jobs than async threads, and use a
single global queue rather than per-thread queues, eliminating the
risk of a job stalling behind a long-running job on the same thread
while other async threads sit idle.
There's no such thing as a free lunch though; the lowered latency
comes at the cost of increased busy-waiting which may have an
adverse effect on some applications. This behavior can be tweaked
with the +sbwt flag, but unfortunately it affects all types of
schedulers and not just dirty ones. We plan to add type-specific
flags at a later stage.
sendfile has been moved to inet_drv to lessen the effect of a nasty
race; the cooperation between inet_drv and efile has never been
airtight and the socket dying at the wrong time (Regardless of
reason) could result in fd aliasing. Moving it to the inet driver
makes it impossible to trigger this by closing the socket in the
middle of a sendfile operation, while still allowing it to be
aborted -- something that can't be done if it stays in the file
driver.
The race still occurs if the controlling process dies in the short
window between dispatching the sendfile operation and the dup(2)
call in the driver, but it's much less likely to happen now.
A proper fix is in the works.
--
Notable functional differences:
* The use_threads option for file:sendfile/5 no longer has any
effect.
* The file-specific DTrace probes have been removed. The same
effect can be achieved with normal tracing together with the
nif__entry/nif__return probes to track scheduling.
--
OTP-14256
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* lukas/erts/pgo/OTP-14604:
erts: Only do PGO if gcc supports -fprofile-correction
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* lukas/erts/poll-thread/OTP-14346:
erts: Make a copy of erl_poll.c to help debuggers
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Especially lldb seems to get very confused when the
same source file is used by two different object files.
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OTP-14327
OTP-14340
* bjorn/erts/pack-with-opcode/OTP-14325:
Pack operands for combined instructions into the instruction word
beam_makeops: Use named arguments for the code generation functions
Optimize packing for "optional use" operands
beam_makeops: Print the instruction name for fatal packing errors
Introduce a syntax for marking operands as "optional use"
beam_makeops: Refactor parsing of specific instructions
Optimize instruction prefetch
Pack operands into the instruction word
Use 32-bits pointers to C code
Move LD flags for hipe from Makefile.in to configure.in
beam_disasm: Correct printing of y registers
ops.tab: Slightly optimize badmatch on a Y register
macros.tab: Fix assertion in SET_I_REL()
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* lukas/erts/beam-emu-vars:
erts: Add makefile target to check emu register allocation
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On 64-bit machines where the C code is always at address below 4Gb,
pack one or more operands into the instruction word.
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We want the flags to be available for other tests in configure.in.
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* lukas/erts/pgo/OTP-14604:
Add support for building a pgo beam_emu
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All operations will now yield appropriately, allowing them to be used
freely in concurrent applications. This commit also deprecates the
functions listed below, although they won't raise deprecation
warnings until OTP 21:
zlib:adler32
zlib:crc32
zlib:inflateChunk
zlib:getBufSize
zlib:setBufSize
The behavior of throwing an error when a dictionary is required for
decompression has also been deprecated.
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The bit syntax instructions are mixed among other instructions
in beam_hot.h and beam_cold.h.
Introduce a new hotness level called '%warm' with is associated
file beam_warm.h. Mark all bit syntax instructions as '%warm'.
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The beam_instrs.h file serves no useful purpose. Put the
instructions in beam_hot.h instead.
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Eliminate the need to write pre-processor macros for each instruction.
Instead allow the implementation of instruction to be written in
C directly in the .tab files. Rewrite all existing macros in this
way and remove the %macro directive.
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* john/erts/runtime-lcnt:
Document rt_mask and add warnings about copy_save
Add an emulator test suite for lock counting
Break erts_debug:lock_counters/1 into separate BIFs
Allow toggling lock counting at runtime
Move lock flags to a common header
Enable register_SUITE for lcnt builds
Enable lcnt smoke test on all builds that have lcnt enabled
Make lock counter info independent of the locks being counted
OTP-14412
OTP-13170
OTP-14413
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If a link dependency is added in LDFLAGS it should be resolved
in LIBS, so we have to use LIBS and not TYPE_LIBS.
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This allows us to enable/disable lock counting at will, and greatly improves
the performance of erts_debug:lock_counters/1 since we no longer have to
worry about the lock counters "dying" while we're enumerating them.
OTP-14412
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in order to regenerate them if config has changed.
ERL-379
Maybe a better solution would have been to run 'clean' target
or stop and ask user to run make clean.
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and no need for $(INCLUDED).
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Just like the BEAM loader state (as returned by
erlang:prepare_loading/2), the HiPE loader state is contained in a magic
binary.
Eventually, we will separate HiPE loading into a prepare and a finalise
phase, like the BEAM loader, where the prepare phase will be implemented
by hipe_unified_loader and the finalise phase be implemented in C by
hipe_load.c and beam_load.c, making prepare side-effect free and
finalise atomic. The finalise phase will be exposed through the
erlang:finish_loading/1 API, just like the BEAM loader, as this will
allow HiPE and BEAM modules to be mixed in the same atomic "commit".
The usage of a loader state makes it easier to keep track of all
resources allocated during loading, and will not only make it easy to
prevent leaks when hipe_unified_loader crashes, but also paves the way
for proper, leak-free, unloading of HiPE modules.
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* maint:
Fix tracing of processes executing dirty
Perform check_process_code while process is executing dirty
Fix purge of code
Reclaim literal area after purge has completed
Separate literal area from code
Conflicts:
erts/emulator/beam/global.h
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* rickard/ds-purge-module/OTP-13808:
Perform check_process_code while process is executing dirty
Conflicts:
erts/doc/src/erl_nif.xml
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'rickard/new-purge-strategy/OTP-13833' into maint
* rickard/fun-purge-bug/OTP-13809:
Fix purge of code
Reclaim literal area after purge has completed
Separate literal area from code
Conflicts:
erts/doc/src/erlang.xml
erts/emulator/beam/beam_bif_load.c
erts/emulator/beam/erl_init.c
erts/preloaded/ebin/init.beam
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