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Introduce is_map_key/2 guard BIF
OTP-15037
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This complements the `map_get/2` guard BIF introduced in #1784.
Rationale.
`map_get/2` allows accessing map fields in guards, but it might be
problematic in more complex guard expressions, for example:
foo(X) when map_get(a, X) =:= 1 or is_list(X) -> ...
The `is_list/1` part of the guard could never succeed since the
`map_get/2` guard would fail the whole guard expression. In this
situation, this could be solved by using `;` instead of `or` to separate
the guards, but it is not possible in every case.
To solve this situation, this PR proposes a `is_map_key/2` guard that
allows to check if a map has key inside a guard before trying to access
that key. When combined with `is_map/1` this allows to construct a
purely boolean guard expression testing a value of a key in a map.
Implementation.
Given the use case motivating the introduction of this function, the PR
contains compiler optimisations that produce optimial code for the
following guard expression:
foo(X) when is_map(X) and is_map_key(a, X) and map_get(a, X) =:= 1 -> ok;
foo(_) -> error.
Given all three tests share the failure label, the `is_map_key/2` and
`is_map/2` tests are optimised away.
As with `map_get/2` the `is_map_key/2` BIF is allowed in match specs.
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* 'map-get-bif' of git://github.com/michalmuskala/otp:
Introduce map_get guard-safe function
OTP-15037
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Improve memory instrumentation
OTP-15024
OTP-14961
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Rationale
Today all compound data types except for maps can be deconstructed in guards.
For tuples we have `element/2` and for lists `hd/1` and `tl/1`. Maps are
completely opaque to guards. This means matching on maps can't be
abstracted into macros, which is often done with repetitive guards. It
also means that maps have to be always selected whole from ETS tables,
even when only one field would be enough, which creates a potential
efficiency issue.
This PR introduces an `erlang:map_get/2` guard-safe function that allows
extracting a map field in guard. An alternative to this function would be
to introduce the syntax for extracting a value from a map that was planned
in the original EEP: `Map#{Key}`.
Even outside of guards, since this function is a guard-BIF it is more
efficient than using `maps:get/2` (since it does not need to set up the
stack), and more convenient from pattern matching on the map (compare:
`#{key := Value} = Map, Value` to `map_get(key, Map)`).
Performance considerations
A common concern against adding this function is the notion that "guards
have to be fast" and ideally execute in constant time. While there are
some counterexamples (`length/1`), what is more important is the fact
that adding those functions does not change in any way the time
complexity of pattern matching - it's already possible to match on map
fields today directly in patterns - adding this ability to guards will
niether slow down or speed up the execution, it will only make certain
programs more convenient to write.
This first version is very naive and does not perform any optimizations.
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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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If messages are not flushed they would cause problems when
the system is booting. For instance module load requests
would be issued before the prim loader has been launched.
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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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* john/erts/list-installed-nifs/OTP-14965:
Add an option to ?MODULE:module_info/1 for listing NIFs
Fix a misleading comment
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* bjorn/erts/eliminate-get_stacktrace:
Eliminate use of erlang:get_stacktrace/0 in preloaded modules
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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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It wasn't possible to change group/owner separately, and our test
suite lacked coverage for that.
ERL-589
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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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Attempt to make the system_info docs easier to navigate
by grouping items of similar themes together in the documentation.
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or backslash on Windows.
Purpose: Prevent tricks to get hostile code running.
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* maint-20:
Updated OTP version
Update release notes
Update version numbers
erts: Add system_flags(erts_alloc,"+M?sbct *")
erts: Add age order first fit allocator strategies
erts: Refactor erl_ao_firstfit_alloc
erts: Add migration options "acnl" and "acfml"
kernel: Add os:cmd/2 with max_size option
erts: Add more stats for mbcs_pool
erts: Fix alloc_SUITE:migration
stdlib: Make ets_SUITE memory check try again
erts: Improve carrier pool search
erts: Improve alloc_SUITE:migration
erts: Refactor carrier dealloc migration
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into 'sverker/master/alloc-n-migration/ERIERL-88'
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into 'sverker/maint-20/alloc-n-migration/ERIERL-88'
OTP-14915
OTP-14916
OTP-14917
OTP-14918
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into 'sverker/maint-19/alloc-n-migration/ERIERL-88'
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to change sbct limit in runtime for chosen allocator type.
With great power comes great responsibility.
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The existing wording may be interpreted as saying that embedded mode
eager loads all modules. This revision makes clear embedded mode only
disables module auto loading.
Since I was on it, I have reordered a couple of places to describe
interactive first, and then embedded. It feels natural to cover first
the default and positive mode (auto loads), and then its negation.
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similar to the ones in OTP-19.2.3.1
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* dgud/kernel/refc_sched_wall_time/OTP-11694:
test: spawn scheduler_wall_time flag holder
Turn on scheduler_wall_time in an alive process
Redirect system_flag(scheduler_wall_time,_) to kernel_refc
kernel: add a resource reference counter
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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/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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