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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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When a module has been purged from memory, any literals belonging
to that module will be copied to all processes that hold references
to them.
The max heap size limit would be ignored in the garbage collection
initiated when copying literals to a process. If the max heap size
was exceeded, the process would typically be terminated in the
following garbage collection.
Since the process would be killed anyway later, kill the process
before copying a literal that would make it exceed its max heap
size.
While at it, also fix a potential bug in `erlang:garbage_collect/0`.
If it was found that the max heap sized had been exceeded while
executing `erlang:garbage_collect/0`, the process would enter a
kind of zombie state instead of being properly terminated.
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If the process had more free space than reductions it could run a
lot longer than it was supposed to. It didn't honor the number of
reductions going in either, nor did it bump reductions when
returning its result or erroring out.
This commit also removes this function from a work function in
scheduler_SUITE as it's extremely sensitive to the number of
reductions spent in the test, causing
equal_and_high_with_part_time_max to fail on some machines.
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* maint-21:
Updated OTP version
Update release notes
Update version numbers
kernel: Fix missing abort_connection in net_kernel
Prevent inconsistent node lists
Fix an endless rescheduling loop when a process is executing process_info(self(), ...)
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If net_kernel "forgets" to abort a connection (as it currently might),
the garbage collection of a distribution entry could cause node lists
to enter an inconsistent state.
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* rickard/fix-suspend-monitor-down/OTP-15237/ERL-704:
Fix incoming suspend monitor down
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An incoming suspend monitor down wasn't handled correct when the
local monitor half had been removed with an emulator crash as result.
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* dotsimon/ref_ordering_bug/OTP-15225:
Fixed #Ref ordering bug
Test #Ref ordering in lists and ets
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A lot of erts internal messages used behind APIs to create
non-blocking calls, e.g. port_command, would cause the seq_trace
token to be cleared from the caller when it should not.
This commit fixes that and adds asserts that makes sure
that all messages sent have to correct token set.
Fixes: ERL-602
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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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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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This is a hack to make the "noshell" option work; kqueue can poll
these fds but will not report EV_EOF. This may be common to all
all pipes but we have no way to tell whether an fd is a pipe or
not.
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* john/erts/merge-OTP-15067:
Don't enqueue system tasks if target process is in fail_state
Fix erroneous schedule of freed/exiting processes
Fix deadlock in run queue evacuation
Fix memory leak of processes that died in the run queue
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into john/erts/merge-OTP-15067
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The fail state wasn't re-checked in the state change loop; only
the FREE state was checked. In addition to that, we would leave
the task in the queue when bailing out which could lead to a
double-free.
This commit backports active_sys_enqueue from master to make it
easier to merge onwards.
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to actually run remote on the slave node that it starts.
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* sverker/system-profile-bug/OTP-15085:
erts: Fix bug in system_profile
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seen to cause redundant {profile,_,active,_,_} messages
when process is terminating.
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Fix bug in enif_binary_to_term for immediates
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epmd: allow alternative to dns resolving for nodename
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This makes it possible to create a custom integration with a
key-value store for example. The key would then point to the
actual address. You would have to write your own epmd module
to make use of that feature.
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* richcarl/eliminate_lib_module/PR-1786/OTP-15072:
Fix minor issues
Eliminate call to ct:get_progname() in ts_erl_config
Use \n escape instead of integer 10
Move error formatting to erl_error.erl and delete lib.erl
Move extended parse functions in lib.erl to erl_eval.erl
Move lib:eval_str/1 into mod_esi.erl
Remove lib:progname/0
Eliminate call to lib:progname/1 in slave.erl
Add ct:get_progname/0
Remove lib:error_message/2
Remove lib:flush_receive/0
Remove lib:send/2 and lib:sendw/2
Move lib:nonl/1 into yecc.erl
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Symptom: Heap corruption
Expanded test case to provoke this bug
and test some more term types.
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Introduce is_map_key/2 guard BIF
OTP-15037
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This replaces all uses of lib:progname/0 in tests.
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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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* siri/kernel/logger/OTP-13295:
Add documentation of the built-in logger handlers
Catch badarg in logger:get_format_depth/0
Add chars_limit option to logger_formatter
Don't kill logger process until all other processes are dead
Set call timeout for logger_server to infinity
Update primary bootstrap
Test cuddle for logger
Update cth_log_redirect to a logger handler
Start using logger internally in kernel and stdlib
Remove error_logger process and add logger process
Add logger
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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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* lukas/erts/poll-thread/OTP-14346:
erts: nif resource stop from poll-thread is a indirect call
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* lukas/erts/dump_SUITE_fix:
erts: Increase file read timeout for signal_abort test
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* john/erts/fix-lcnt-toggle-test:
Disregard locks that can't be toggled in lcnt_SUITE
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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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* lukas/erts/seq_tracer_nif/OTP-15029:
Fix seq_trace erl_tracer bug
Fix makefile mkdir warning
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