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Implementation of true asynchronous signaling between processes
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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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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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Remove unused cerl_messagean module
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Conflicts:
OTP_VERSION
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Eliminate get_list/3 internally in the compiler
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Currently HiPE amd64 assumes the runtime system code is loaded into
the low 2G of the address space. However, this is not the case when
PIE is enabled, it is loaded into a random location. So trampolines
are required to call BIFs, and also we have first to load the address
of sse2_fnegate_mask to a regisiter before xorpd in fchs.
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Make hipe compile option verify_gcsafe the default
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Instructions that produce more than one result complicate
optimizations. get_list/3 is one of two instructions that
produce multiple results (get_map_elements/3 is the other).
Introduce the get_hd/2 and get_tl/2 instructions
that return the head and tail of a cons cell, respectively,
and use it internally in all optimization passes.
For efficiency, we still want to use get_list/3 if both
head and tail are used, so we will translate matching pairs
of get_hd and get_tl back to get_list instructions.
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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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* maint:
ErLLVM: Preserve precise BEAM tailcall semantics
observer: Fix change accum
Remove double calls
observer: Don't crash for late messages
observer: Optimize tv tab for many tables
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The BEAM compiler chooses not to perform tailcall optimisations for some
calls in tail position, for example to some built-in functions. However,
when the ErLLVM HiPE backend is used, LLVM may choose to perform
tailcall optimisation on these calls, breaking the expected semantics.
To preserve the precise semantics exhibited by BEAM, the 'notail'
marker, present in LLVM since version 3.8, is added to call instructions
that BEAM has not turned into tail calls, which inhibits LLVM from
performing tail-call optimisation in turn.
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* maint:
dialyzer: Fix bsl/2 bug
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* hasse/dialyzer/fix_bsl:
dialyzer: Fix bsl/2 bug
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which is has been since 3d21f793538927ae88f78504a11dd898e8ca1a7a
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Also modified erl_bif_types:infinity_bsl() when called with zero as
first argument. As of writing this, erlang:'bsl'/2 is modified on the
master branch to never fail if called with a huge second argument.
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* maint:
dialyzer: Correct handling of erlang:abs/1
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See also https://bugs.erlang.org/browse/ERL-551.
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by preventing it from doing GC, which generated code relies on.
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This commit adds a new syntax for retrieving the stacktrace
without calling erlang:get_stacktrace/0. That allow us to
deprecate erlang:get_stacktrace/0 and ultimately remove it.
The problem with erlang:get_stacktrace/0 is that it can keep huge
terms in a process for an indefinite time after an exception. The
stacktrace can be huge after a 'function_clause' exception or a failed
call to a BIF or operator, because the arguments for the call will be
included in the stacktrace. For example:
1> catch abs(lists:seq(1, 1000)).
{'EXIT',{badarg,[{erlang,abs,
[[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20|...]],
[]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]}}
2> erlang:get_stacktrace().
[{erlang,abs,
[[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
23,24|...]],
[]},
{erl_eval,do_apply,6,[{file,"erl_eval.erl"},{line,674}]},
{erl_eval,expr,5,[{file,"erl_eval.erl"},{line,431}]},
{shell,exprs,7,[{file,"shell.erl"},{line,687}]},
{shell,eval_exprs,7,[{file,"shell.erl"},{line,642}]},
{shell,eval_loop,3,[{file,"shell.erl"},{line,627}]}]
3>
We can extend the syntax for clauses in try/catch to optionally bind
the stacktrace to a variable.
Here is an example using the current syntax:
try
Expr
catch C:E ->
Stk = erlang:get_stacktrace(),
.
.
.
In the new syntax, it would look like:
try
Expr
catch
C:E:Stk ->
.
.
.
Only a variable (not a pattern) is allowed in the stacktrace position,
to discourage matching of the stacktrace. (Matching would also be
expensive, because the raw format of the stacktrace would have to be
converted to the cooked form before matching.)
Note that:
try
Expr
catch E ->
.
.
.
is a shorthand for:
try
Expr
catch throw:E ->
.
.
.
If the stacktrace is to be retrieved for a throw, the 'throw:'
prefix must be explicitly included:
try
Expr
catch throw:E:Stk ->
.
.
.
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* maint:
dialyzer: Extend the map implementation's handling of ?unit
dialyzer: Use string:find() instead of string:str()
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The Maps implementation handles ?unit in more cases.
Exactly when t_is_none_or_unit() is to be called is not clear to me.
The added cases are about a map type being ?unit, but the key or the
value of an association can also be ?unit, but that is not always
checked.
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HiPE: Optimise receives matching unique references
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* lukas/docs/xmllint_fixes/OTP-14721:
ssl/ssh: Remove/ignore unused XML_FILES doc files
Refactor xmllint check and make it fail on failure
Add toplevel xmllint make target
Conflicts:
lib/crypto/doc/src/Makefile
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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 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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HiPE: Support for literal tag, tests and bugfixes
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Document HiPE limitations
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Literal tags are used by the VM as an alternative to reserving a large
virtual memory space in order to be able to quickly identify which terms
are literals. The use of literal tags harms performance, but is useful
to support systems where allocating a large amount of virtual memory is
not an option.
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HiPE has had metadata for gc safety on it's temporaries for a while, but
it has never been enforced or even checked, so naturally several
gc-safety violations has slipped through.
A new pass, hipe_rtl_verify_gcsafe verifies gcsafety on optimised RTL
and is used when running the testsuite, and can be manually enabled with
+{hipe,[verify_gcsafe]}.
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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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During deletion, the killing of expressions was not considered.
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The lazy code motion optimisation pass could violate its guarantees
eliminating partial redundancy by moving an expression to before a call
instruction.
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