From 708bfd21156828526fe72de2cedecfaca6647dc1 Mon Sep 17 00:00:00 2001
From: normal <normal@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 29 Jul 2018 20:47:33 +0000
Subject: thread_pthread: remove timer-thread by restructuring GVL

To reduce resource use and reduce CI failure; remove
timer-thread.  Single-threaded Ruby processes (including forked
children) will never see extra thread overhead.  This prevents
glibc and jemalloc from going into multi-threaded mode and
initializing locks or causing fragmentation via arena explosion.

The GVL is implements its own wait-queue as a ccan/list to
permit controlling wakeup order.  Timeslice under contention is
handled by a designated timer thread (similar to choosing a
"patrol_thread" for current deadlock checking).

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

Signal handling is handled directly by a 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) for this.  Unfortunately, this
proved unfeasible as Mutex#sleep resumes on spurious wakeups and
test/thread/test_cv.rb::test_condvar_timed_wait failed.  Using
pthread_sigmask to mask out SIGVTALRM fixed that test,  but
test/fiddle/test_function.rb::test_nogvl_poll proved there'd be
some unavoidable (and frequent) incompatibilities from that
approach.

Finally, this allows us to drop thread_destruct_lock and
interrupt current ec directly.

We don't need to rely on vm->thread_destruct_lock or a coherent
vm->running_thread on any platform.  Separate timer-thread for
time slice and signal handling is relegated to thread_win32.c,
now.

[ruby-core:88088] [Misc #14937]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64107 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 thread_win32.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

(limited to 'thread_win32.c')

diff --git a/thread_win32.c b/thread_win32.c
index 2d5eac1ff4..3770200d30 100644
--- a/thread_win32.c
+++ b/thread_win32.c
@@ -20,6 +20,7 @@
 
 #define native_thread_yield() Sleep(0)
 #define unregister_ubf_list(th)
+#define ubf_wakeup_all_threads() do {} while (0)
 
 static volatile DWORD ruby_native_thread_key = TLS_OUT_OF_INDEXES;
 
@@ -680,18 +681,21 @@ static struct {
 static unsigned long __stdcall
 timer_thread_func(void *dummy)
 {
+    rb_vm_t *vm = GET_VM();
     thread_debug("timer_thread\n");
     rb_w32_set_thread_description(GetCurrentThread(), L"ruby-timer-thread");
     while (WaitForSingleObject(timer_thread.lock, TIME_QUANTUM_USEC/1000) ==
 	   WAIT_TIMEOUT) {
-	timer_thread_function(dummy);
+	timer_thread_function();
+	ruby_sigchld_handler(vm); /* probably no-op */
+	rb_threadptr_check_signal(vm->main_thread);
     }
     thread_debug("timer killed\n");
     return 0;
 }
 
 void
-rb_thread_wakeup_timer_thread(void)
+rb_thread_wakeup_timer_thread(int sig)
 {
     /* do nothing */
 }
@@ -768,6 +772,25 @@ rb_reserved_fd_p(int fd)
     return 0;
 }
 
+int
+rb_sigwait_fd_get(rb_thread_t *th)
+{
+    return -1; /* TODO */
+}
+
+void
+rb_sigwait_fd_put(rb_thread_t *th, int fd)
+{
+    rb_bug("not implemented, should not be called");
+}
+
+
+void
+rb_sigwait_sleep(const rb_thread_t *th, int fd, const struct timespec *ts)
+{
+    rb_bug("not implemented, should not be called");
+}
+
 rb_nativethread_id_t
 rb_nativethread_self(void)
 {
-- 
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