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Misc #14937

closed

[PATCH] thread_pthread: lazy-spawn timer-thread only on contention

Added by normalperson (Eric Wong) over 6 years ago. Updated over 6 years ago.

Status:
Closed
Assignee:
-
[ruby-core:88088]

Description

[ruby-core:87773]

thread_pthread: lazy-spawn timer-thread only on contention

To reduce resource use and reduce CI failure; lazy spawn
timer-thread only in processes which use Ruby Threads AND those
Ruby Threads hit contention.  Single-threaded Ruby processes
(including forked children) will never have timer-thread
overhead.

To simplify the thread_pthread.c code, I eliminated busy timer
thread [Misc #14851].  Maybe the thread_win32.c code can use
self-pipe, too; and they won't need busy wakeups.

There is only one self-pipe, now, as wakeups for timeslice are
handled via condition variables.  This reduces FD pressure
slightly.

Signal handling is handled directly by one Ruby Thread (instead
of timer-thread) by exposing signal self-pipe to callers of
rb_thread_fd_select, native_sleep, rb_wait_for_single_fd, etc...
Acquiring, using, and releasing the self-pipe is exposed via 4
new internal functions:

1) rb_sigwait_fd_get - exclusively acquire timer_thread_pipe.normal[0]

2) rb_sigwait_fd_sleep - sleep and wait for signal (and no other FDs)

3) rb_sigwait_fd_put - release acquired result from rb_sigwait_fd_get

4) rb_sigwait_fd_migrate - migrate signal handling to another thread
		       after calling rb_sigwait_fd_put.

rb_sigwait_fd_migrate is necessary for waitpid callers because
only one thread can wait on self-pipe at a time, otherwise a
deadlock will occur if threads fight over the self-pipe.

TRAP_INTERRUPT_MASK is now set for the main thread directly in
signal handler via rb_thread_wakeup_timer_thread.

Originally, I wanted to use POSIX timers
(timer_create/timer_settime) and avoid timer-thread completely.
Unfortunately, this proved unfeasible for one reason:
Mutex#sleep resumes on spurious wakeups and
test/thread/test_cv.rb::test_condvar_timed_wait failed.

In the future, I hope [Feature #14717] is accepted so Threads
may be made non-preemptible.  This will allow users to prevent
timer-thread creation completely.

git repository also available at:
https://80x24.org/ruby.git tt-lazy
(commit a2990cefccba55300ad44275ee4adf18e6f95ece)

Files

0001-thread_pthread-lazy-spawn-timer-thread-only-on-conte.patch (42.3 KB) 0001-thread_pthread-lazy-spawn-timer-thread-only-on-conte.patch normalperson (Eric Wong), 07/24/2018 11:48 PM
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