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* rickard/process_info/OTP-14966:
Fix scheduled process_info() 'status' request
Fix handling of process-info requests in receive
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* rickard/process_info/OTP-14966:
New process_info() implementation using signals
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jhogberg/john/erts/any-term-as-seq_trace-label/OTP-14899
Lift the type restrictions on seq_trace token labels
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OTP-14899
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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The previously used message queue partitioned into two halves has been
replaced by a more general signal queue partitioned into three parts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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When a ref is created before performing a receive that will only
receive message containing that ref, there is a compiler optimization
to avoid scanning messages that can't possible contain the newly
created ref.
Magnus Lång pointed out that the implementation of the optimization
is flawed. Exceptions or recursive calls could cause the receive
operation to scan the receive queue from a position beyond the expected
message (that is, the message containing the ref would never be
matched out). See the receive_opt_exception/1 and receive_opt_recursion/1
test cases in receive_SUITE.
It turns out that we can simplify the implementation of the
optimization while fixing the bug (suggested by Magnus Lång). We
actually don't need the c_p->msg.mark field. It is enough to have
c_p->msg.saved_pos; if it is non-zero, it is a valid position in the
message qeueue. All we need to do is to ensure that we clear
c_p->msg.saved_pos when a receive is exited normally or abnormally.
We can clear c_p->msg.saved_pos in JOIN_MESSAGE(), since it is called
both when leaving a receive because a message matched and because there
was a timeout and the 'after' clause was executed. In addition, we
need to clear c_p->msg.saved_pos when an exception is caught.
https://bugs.erlang.org/browse/ERL-511
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Introduce new macros that can be used for relative jumps and
use them consistently.
Test that everything works by using a non-zero constant JUMP_OFFSET.
The loader subtracts JUMP_OFFSET from loaded labels, and all
instructions that use 'f' operands add it back.
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We KNOW that recv_set instruction is immediately followed
by a loop_rec instruction.
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