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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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* raimo/tcp-close-while-send/maint/ERL-561/OTP-12242:
Write test case
Fix hanging gen_tcp send vs close race
Conflicts:
erts/preloaded/ebin/prim_inet.beam
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While a gen_tcp send was in progress with filled buffers
and slow receiver a close (from another process) would place
the port in a half dead state so the port could not signal
back to send, that waited for confirmation.
The solution is to after some time (5 s) of waiting for
send confirmation set a monitor on the port, which detects
if the port becomes half dead due to close from another process.
The close pending loop has also been improved to use the linger
timeout for waiting, and to set a system timeout (arbitrarily
selected 3 min) to not wait forever when the other end
reads data s l o w l y (tarpitting, kind of).
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* igor/tcp-nopush-ERL-698/OTP-15357:
"cork" tcp socket around file:sendfile
Add nopush TCP socket option
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This fixes 200ms delay on the last TCP segment when using
file:sendfile/2 on Linux (ERL-698).
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This translates to TCP_CORK on Linux and TCP_NOPUSH on
BSD.
In effect, this acts as super-Nagle: no partial TCP segments
are sent out until this option is turned off. Once turned off,
all accumulated unsent data is sent out immediately. The latter
is *not* the case on OSX, hence the implementation ignores
"nopush" on OSX to reduce confusion.
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Also implement the same option for the legacy undocumented functions
inet:getif/1,getiflist/1,ifget/2,ifset/2.
The arity 1 functions had before this change got signatures that
took a socket port that was used to do the needed syscall, so now
the signature was extended to also take an option list with the
only supported option {netns,Namespace}. The Socket argument
variant remains unsupported.
For inet:getifaddrs/1 the documentation file was changed to old
style function name definition so be able to hide the Socket
argument variant that is visible in the type spec.
The arity 2 functions had got an option list as second argument.
This list had to be partitioned into one list for the namespace
option(s) and the other for the rest.
The namespace option list was then fed to the already existing
namespace support for socket opening, which places the socket
in a namespace and hence made all these functions that in
inet_drv.c used getsockopt() work without change.
The functions that used getifaddrs() in inet_drv.c had to be
changed in inet_drv.c to swap namespaces around the
getifaddrs() syscall. This functionality was separated into
a new function call_getifaddrs().
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* sverker/erts/robustify-dist-entry-states/OTP-15297:
erts: Refactor port dist_entry & conn_id into PRTSD
Remove ugly fail case macros
Consolidate distribution entry state transitions
erts: Fix bug in undocumented system_flag(scheduling_statistics)
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* Make connection_id part of the distribution handle as {ConnId, DistEntry}
in order for BIFs to verify correct connection.
* Make distribution handle opaque to net_kernel.
* Remove some unsafe lockless reads of DistEntry.flags
* Change state ERTS_DE_STATE_EXITING to be more of an internal state that
prevents erts from enqueue, encode or schedule new data to be sent. Otherwise
it should behave like ERTS_DE_STATE_CONNECTED.
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* raimo/receive-TOS-TCLASS/ERIERL-187/OTP-15145:
Write testcases for recvtos and friends
Fix term buffer overflow bug
Fix documentation due to feedback
Implement socket option recvtos and friends
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We said reverse/2 but used reverse/1 which is unsafe to use in
preloaded modules. This didn't have any effect in practice as the
affected functions weren't used before the code server was started,
but it's still an error.
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Implement socket options recvtclass, recvtos, recvttl and pktoptions.
Document the implemented socket options, new types and message formats.
The options recvtclass, recvtos and recvttl are boolean options that
when activated (true) for a socket will cause ancillary data to be
received through recvmsg(). That is for packet oriented sockets
(UDP and SCTP).
The required options for this feature were recvtclass and recvtos,
and recvttl was only added to test that the ancillary data parsing
handled multiple data items in one message correctly.
These options does not work on Windows since ancillary data
is not handled by the Winsock2 API.
For stream sockets (TCP) there is no clear connection between
a received packet and what is returned when reading data from
the socket, so recvmsg() is not useful. It is possible to get
the same ancillary data through a getsockopt() call with
the IPv6 socket option IPV6_PKTOPTIONS, on Linux named
IPV6_2292PKTOPTIONS after the now obsoleted RFC where it originated.
(unfortunately RFC 3542 that obsoletes it explicitly undefines
this way to get packet ancillary data from a stream socket)
Linux also has got a way to get packet ancillary data for IPv4
TCP sockets through a getsockopt() call with IP_PKTOPTIONS,
which appears to be Linux specific.
This implementation uses a flag field in the inet_drv.c socket
internal data that records if any setsockopt() call with recvtclass,
recvtos or recvttl (IPV6_RECVTCLASS, IP_RECVTOS or IP_RECVTTL)
has been activated. If so recvmsg() is used instead of recvfrom().
Ancillary data is delivered to the application by a new return
tuple format from gen_udp:recv/2,3 containing a list of
ancillary data tuples [{tclass,TCLASS} | {tos,TOS} | {ttl,TTL}],
as returned by recvmsg(). For a socket in active mode a new
message format, containing the ancillary data list, delivers
the data in the same way.
For gen_sctp the ancillary data is delivered in the same way,
except that the gen_sctp return tuple format already contained
an ancillary data list so there are just more possible elements
when using these socket options. Note that the active mode
message format has got an extra tuple level for the ancillary
data compared to what is now implemented gen_udp.
The gen_sctp active mode format was considered to be the odd one
- now all tuples containing ancillary data are flat,
except for gen_sctp active mode.
Note that testing has not shown that Linux SCTP sockets deliver
any ancillary data for these socket options, so it is probably
not implemented yet. Remains to be seen what FreeBSD does...
For gen_tcp inet:getopts([pktoptions]) will deliver the latest
received ancillary data for any activated socket option recvtclass,
recvtos or recvttl, on platforms where IP_PKTOPTIONS is defined
for an IPv4 socket, or where IPV6_PKTOPTIONS or IPV6_2292PKTOPTIONS
is defined for an IPv6 socket. It will be delivered as a
list of ancillary data items in the same way as for gen_udp
(and gen_sctp).
On some platforms, e.g the BSD:s, when you activate IP_RECVTOS
you get ancillary data tagged IP_RECVTOS with the TOS value,
but on Linux you get ancillary data tagged IP_TOS with the
TOS value. Linux follows the style of RFC 2292, and the BSD:s
use an older notion. For RFC 2292 that defines the IP_PKTOPTIONS
socket option it is more logical to tag the items with the
tag that is the item's, than with the tag that defines that you
want the item. Therefore this implementation translates all
BSD style ancillary data tags to the corresponding Linux style
data tags, so the application will only see the tags 'tclass',
'tos' and 'ttl' on all platforms.
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to include ports and NIF resources.
Added new opaque type 'nif_resource'.
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* sverker/erlang-memory-fix:
erts: Purge unused allocation types
erts: Fix erlang:memory for 'processes' and 'processes_used'
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to include links and monitors which were lost at
4bc282d812cc2c49aa3e2d073e96c720f16aa270
where these fix_alloc types changed names.
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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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