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This patch optimizes map operations to not allocate new maps
when the key is being replaced by the exact same value in memory.
Imagine this very common idiom:
Map#{key := compute_new_value(Value, Condition)}
where:
compute_new_x(X, true) -> X + 1;
compute_new_x(X, false) -> X;
In many cases, we are not changing the value in `Key`, however
the code prior to this patch would still allocate a new array
for the map values. This optimization changes this.
The cost of optimization is minimum, as in the worst case scenario
it only adds a pointer comparison and boolean check. The major benefit
is reducing the GC pressure by avoiding allocating data.
Next we list the operations we have changed alongside the benchmark
results. The benchmarks basically create a map and perform the same
operations, roughly 20000 times, once replacing the key with the same
value, and another with a different value.
* Map#{Key := Value}
For a map with 4 keys, replacing the fourth key 20000 times went from
718us to 539us.
For a map with 8 keys, replacing the fourth key 20000 times went from
976us to 555us.
* maps:update/3
For a map with 4 keys, replacing the fourth key 20000 times went from
673us to 575us.
For a map with 8 keys, replacing the fourth key 20000 times went from
827us to 585us.
* maps:put/3
For a map with 4 keys, replacing the fourth key 20000 times went from
763us to 553us.
For a map with 8 keys, replacing the fourth key 20000 times went from
788us to 561us.
Note that we have ported some optimizations found in maps:update/3
to maps:put/3 while creating this patch.
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* maint:
Fix typo in xmerl_scan:string/1
Updated OTP version
Prepare release
ssl: Engine key trumps certfile option
inets: Prepare for release
inets: Improve error handling
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* maint-20:
Updated OTP version
Prepare release
ssl: Engine key trumps certfile option
inets: Prepare for release
inets: Improve error handling
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maps:new/0 is no longer a BIF
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* sverker/crash-dump-crash-literals/OTP-15181:
erts: Fix bug in crash dump generation
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* john/erts/inet-drv-race/OTP-15158/ERL-654:
Fix a race condition when generating async operation ids
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* sverker/erl_interface/valgrind/OTP-15171:
erl_interface: Fix bug in ei_*receive_msg* functions
erl_interface: Seal test case memory leaks
erl_interface: Initialize erl_errno to zero
erts: Remove use of VALGRIND_PRINTF_XML
erl_interface: Add valgrind ability for test port programs
erts: Fix benign bug in cerl for valgrind
erts: Fix buggy calls to erts_sys_explicit_8bit_getenv
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which only existed in a patched version of valgrind (by pan)
no longer used.
Instead we use standard VALGRIND_PRINTF which will end up like this
if valgrind log format is XML and valgrind version >= 3.9:
<clientmsg>
<tid>7</tid>
<threadname>3_scheduler</threadname>
<text>Test case #20 ei_encode_SUITE:test_ei_encode_long/1
</text>
</clientmsg>
Note the extra trailing whitespace that may occure before </text>.
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* john/erts/kqueue-stdin-polling/OTP-15169/ERL-647:
Use fallback pollset for stdin and friends when using kqueue
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* john/erts/fix-literal-map-elements/OTP-15184:
Fix a rare crash when matching on literal maps
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Optimise creation of anonymous functions
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Implementing it in Erlang allows taking advantage of the literal pool
optimisation, this means the function implemented in Erlang does no
allocations, while the BIF had to allocate new map each time it was
called. Benchmarks show the function is also slightly faster now.
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This introduces a similar optimisation for normal funs
to what was introduced for external funs in #1725.
It is possible to allocate the fun as a literal, if it does not capture
the environment (i.e. it does not close over any variables).
Unfortunately it's not possible to do this in the compiler due to
problems with representation of such functions in the `.beam` files.
Fortunately, we can do this in the loader.
Simple evaluation shows that functions that don't capture the
enviornment consistute over 60% of all funs in the source code of
Erlang/OTP itself.
The only downside is that we lose a meningful value in the `pid` field
of the fun. The goal of this field, beyond debugging, was to be
able to identify the original node of a function. To be able to still do
this, the functions that are created in the loader are assigned the init
pid as the creator.
To solve issues with staryp, initially set the `erts_init_process_id`
to `ERTS_INVALID_PID` and skip the described optimisation if the value
is still uninitialised.
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* sverker/crash-dump-crash-literals/OTP-15181:
erts: Fix bug in crash dump generation
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Only SCPT should keep the recv buffer when going into
select. If UDP does it, it will result in many more
memory allocations than there should be which can be
very detrimental to performance.
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* lukas/clean_doc_xmldir/OTP-15190:
docs: make clean all XMLDIR
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This bug was introduced in 988f5f5e8061ce2. The aux_thread
needs to be poked as it is the thread that handles all
break actions.
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* maint:
Updated OTP version
Update release notes
Update version numbers
Fix trace_info/2
Provide build support for standalone corba repo
Fix release notes for OTP-21.0.2
Move to a dirty scheduler even when we have pending system tasks
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* maint-21:
Updated OTP version
Update release notes
Update version numbers
Fix trace_info/2
Provide build support for standalone corba repo
Fix release notes for OTP-21.0.2
Move to a dirty scheduler even when we have pending system tasks
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When matching on a literal map, the map is placed into the general
scratch register first. This is fine in isolation, but when the
key to be matched was in a Y register it would also be placed in
the scratch register, overwriting the map and crashing the
emulator.
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* john/erts/fix-dirty-reschedule-bug/OTP-15154:
Move to a dirty scheduler even when we have pending system tasks
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* john/erts/fix-21.0.2-release-notes:
Fix release notes for OTP-21.0.2
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* rickard/trace-info-bug/OTP-15183:
Fix trace_info/2
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* rickard/corba-build/OTP-15176:
Provide build support for standalone corba repo
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* john/erts/adjust-fix-alloc-sizes:
Adjust fix_alloc sizes to guarantee they fit a dd block
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Symptom: emulator core dumps during crash dump generation.
Problem:
erts_dump_lit_areas did not grow correctly
to always be equal or larger than number of loaded modules.
The comment about twice the size to include both curr and old
did not seem right. The beam_ranges structure contains *all* loaded
module instances until they are removed when purged.
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* sverker/erts/monitored_by-docs/ERL-648/OTP-15180:
os_mon: Fix volatile test cpu_sup_SUITE:util_api
erts: Fix spec and docs for process_info 'monitored_by'
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* sverker/erts/cpool-simplify:
erts: Simplify calc of allctr->cpool.abandon_limit
erts: Simplify cpool_fetch
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benign until valgrind version 4.* shows up.
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Two of them only affect valgrind builds
and the one for ERL_CRASH_DUMP_NICE seems benign.
Return value changed in c2d70945dce9cb09d5d7120d6e9ddf7faac8d230
old -> new
-1 -> 0 not found
0 -> 1 found ok
1 -> -1 found but too big
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to include ports and NIF resources.
Added new opaque type 'nif_resource'.
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This failed on 32-bit builds, and wasn't noticed because 32-bit
debug builds didn't run during the test period.
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* maint:
erts: Correct The Abstract Format
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* hasse/erts/correct_absform:
erts: Correct The Abstract Format
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* maint:
Call test_lib:recompile/1 from init_per_suite/1
beam_debug: Fix printing of floating point registers
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