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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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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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Magic references are *intentionally* indistinguishable from ordinary
references for the Erlang software. Magic references do not change
the language, and are intended as a pure runtime internal optimization.
An ordinary reference is typically used as a key in some table. A
magic reference has a direct pointer to a reference counted magic
binary. This makes it possible to implement various things without
having to do lookups in a table, but instead access the data directly.
Besides very fast lookups this can also improve scalability by
removing a potentially contended table. A couple of examples of
planned future usage of magic references are ETS table identifiers,
and BIF timer identifiers.
Besides future optimizations using magic references it should also
be possible to replace the exposed magic binary cludge with magic
references. That is, magic binaries that are exposed as empty
binaries to the Erlang software.
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Instead of passing around a file descriptor
use a function pointer to facilitate more advanced
backend write logic such as size limitation or compression.
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This is mostly a pure refactoring.
Except for the buggy cases when calling erlang:halt() with a positive
integer in the range -(INT_MIN+2) to -INT_MIN that got confused with
ERTS_ABORT_EXIT, ERTS_DUMP_EXIT and ERTS_INTR_EXIT.
Outcome OLD erl_exit(n, ) NEW erts_exit(n, )
------- ------------------- -------------------------------------------
exit(Status) n = -Status <= 0 n = Status >= 0
crashdump+abort n > 0, ignore n n = ERTS_ERROR_EXIT < 0
The outcome of the old ERTS_ABORT_EXIT, ERTS_INTR_EXIT and
ERTS_DUMP_EXIT are the same as before (even though their values have
changed).
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OTP-13167
* sverk/proc-dict-opt:
erts: Add new test case pdict_SUITE:mixed
erts: Add 'fill_heap' to erts_debug:state_internal_state
erts: Rename proc dict size to arraySize
erts: Refactor proc dict with 'usedSlots'
erts: Add sizeMask for faster proc dict indexing
erts: Remove ProcDict.used
erts: Add proc dict macros ERTS_PD_START/SIZE
erts: Optimize away function "array_put" in proc dict
erts: Optimize hashing in process dictionary
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* rickard/ohmq/OTP-13047:
Fragmented young heap generation and off_heap_message_queue option
Refactor GC
Introduce literal tag
Conflicts:
erts/doc/src/erlang.xml
erts/emulator/beam/erl_gc.c
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* The youngest generation of the heap can now consist of multiple
blocks. Heap fragments and message fragments are added to the
youngest generation when needed without triggering a GC. After
a GC the youngest generation is contained in one single block.
* The off_heap_message_queue process flag has been added. When
enabled all message data in the queue is kept off heap. When
a message is selected from the queue, the message fragment (or
heap fragment) containing the actual message is attached to the
youngest generation. Messages stored off heap is not part of GC.
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Conflicts:
erts/emulator/beam/erl_printf_term.c
erts/emulator/beam/erl_term.c
erts/emulator/beam/utils.c
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If the process stack contained a match state
the print function would crash the vm as it was not
recognized by tag_val_def().
Add new MATCHSTATE_DEF returned by tag_val_def().
All other callers either ignore it or has a default
clause to handle invalid terms.
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Being able to disable garbage collection over context
switches vastly simplifies implementation of yielding
native code that builds large or complex data structures
on the heap. This since the heap can be left in an
inconsistent state over the context switch.
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rickard/r16/port-optimizations/OTP-10336
* rickard/port-optimizations/OTP-10336:
Change annotate level for emacs-22 in cerl
Update etp-commands
Add documentation on communication in Erlang
Add support for busy port message queue
Add driver callback epilogue
Implement true asynchronous signaling between processes and ports
Add erl_drv_[send|output]_term
Move busy port flag
Use rwlock for driver list
Optimize management of port tasks
Improve configuration of process and port tables
Remove R9 compatibility features
Use ptab functionality also for ports
Prepare for use of ptab functionality also for ports
Atomic port state
Generalize process table implementation
Implement functionality for delaying thread progress from unmanaged threads
Conflicts:
erts/doc/src/erl_driver.xml
erts/doc/src/erlang.xml
erts/emulator/beam/beam_bif_load.c
erts/emulator/beam/beam_bp.c
erts/emulator/beam/beam_emu.c
erts/emulator/beam/bif.c
erts/emulator/beam/copy.c
erts/emulator/beam/erl_alloc.c
erts/emulator/beam/erl_alloc.types
erts/emulator/beam/erl_bif_info.c
erts/emulator/beam/erl_bif_port.c
erts/emulator/beam/erl_bif_trace.c
erts/emulator/beam/erl_init.c
erts/emulator/beam/erl_message.c
erts/emulator/beam/erl_port_task.c
erts/emulator/beam/erl_process.c
erts/emulator/beam/erl_process.h
erts/emulator/beam/erl_process_lock.c
erts/emulator/beam/erl_trace.c
erts/emulator/beam/export.h
erts/emulator/beam/global.h
erts/emulator/beam/io.c
erts/emulator/sys/unix/sys.c
erts/emulator/sys/vxworks/sys.c
erts/emulator/test/port_SUITE.erl
erts/etc/unix/cerl.src
erts/preloaded/ebin/erlang.beam
erts/preloaded/ebin/prim_inet.beam
erts/preloaded/src/prim_inet.erl
lib/hipe/cerl/erl_bif_types.erl
lib/kernel/doc/src/inet.xml
lib/kernel/src/inet.erl
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The hybrid heap emulator was last working in the non-SMP R11B
run-time system. When the constant pools were introduced in R12B,
the hybrid heap emulator was not updated to handle them.
At this point, the harm from reduced readability of the code is
greater than any potential usefulness of keeping the code.
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New NIF features:
Send messages from a NIF, or from thread created by NIF, to any local
process (enif_send)
Store terms between NIF calls (enif_alloc_env, enif_make_copy)
Create binary terms with user defined memory management
(enif_make_resource_binary)
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Store Erlang terms in 32-bit entities on the heap, expanding the
pointers to 64-bit when needed. This works because all terms are stored
on addresses in the 32-bit address range (the 32 most significant bits
of pointers to term data are always 0).
Introduce a new datatype called UWord (along with its companion SWord),
which is an integer having the exact same size as the machine word
(a void *), but might be larger than Eterm/Uint.
Store code as machine words, as the instructions are pointers to
executable code which might reside outside the 32-bit address range.
Continuation pointers are stored on the 32-bit stack and hence must
point to addresses in the low range, which means that loaded beam code
much be placed in the low 32-bit address range (but, as said earlier,
the instructions themselves are full words).
No Erlang term data can be stored on C stacks (enforced by an
earlier commit).
This version gives a prompt, but test cases still fail (and dump core).
The loader (and emulator loop) has instruction packing disabled.
The main issues has been in rewriting loader and actual virtual
machine. Subsystems (like distribution) does not work yet.
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This is the first step in the implementation of the half-word emulator,
a 64-bit emulator where all pointers to heap data will be stored
in 32-bit words. Code specific for this emulator variant is
conditionally compiled when the HALFWORD_HEAP define has
a non-zero value.
First force all pointers to heap data to fall into a single 32-bit range,
but still store them in 64-bit words.
Temporary term data stored on C stack is moved into scheduler specific
storage (allocated as heaps) and macros are added to make this
happen only in emulators where this is needed. For a vanilla VM the
temporary terms are still stored on the C stack.
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fragments was created. This will mainly benefit NIFs that return
large compound terms.
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