diff options
author | normal <normal@b2dd03c8-39d4-4d8f-98ff-823fe69b080e> | 2018-08-25 21:59:30 +0000 |
---|---|---|
committer | normal <normal@b2dd03c8-39d4-4d8f-98ff-823fe69b080e> | 2018-08-25 21:59:30 +0000 |
commit | 70a8a6d3eb20e4b251191d8cae06ee2453458253 (patch) | |
tree | 645ffff26e0f1635b0000705c170ab3f11ba30a4 /thread_pthread.c | |
parent | 49309733e2403911c5812cd4f93754058cb57524 (diff) |
thread_pthread.c: main thread always gets hit by signals
We need to ensure Signal.trap handlers can function if the main
thread is sleeping after a subthread has grabbed sigwait_fd,
but later exited.
Consider the following timeline:
main_thread sub-thread
-----------------------------------------
Signal.trap() { ... }
get sigwait_fd
ppoll on sigwait_fd
native_cond_sleep
(via pthread_cond_wait)
ppoll times-out
put sigwait_fd
sub-thread exits
only thread alive
SIGNAL HITS
The problem is pthread_cond_wait cannot return EINTR,
so we can never run the Signal.trap handler. So we
will avoid using native_cond_sleep in the main thread
and always use ppoll to sleep when in the main thread.
This can guarantee the main thread remains aware of
signals; even if it cannot safely read off sigwait_fd
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64538 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Diffstat (limited to 'thread_pthread.c')
-rw-r--r-- | thread_pthread.c | 42 |
1 files changed, 41 insertions, 1 deletions
diff --git a/thread_pthread.c b/thread_pthread.c index 209ed6781c..92ec66af1e 100644 --- a/thread_pthread.c +++ b/thread_pthread.c @@ -1911,7 +1911,7 @@ rb_sigwait_fd_get(const rb_thread_t *th) return signal_self_pipe.normal[0]; } } - return -1; /* avoid thundering herd */ + return -1; /* avoid thundering herd and work stealing/starvation */ } void @@ -1996,6 +1996,43 @@ rb_sigwait_sleep(rb_thread_t *th, int sigwait_fd, const struct timespec *ts) } } +/* + * This function does not exclusively acquire sigwait_fd, so it + * cannot safely read from it. However, it can be woken up in + * 4 ways: + * + * 1) ubf_select (from another thread) + * 2) rb_thread_wakeup_timer_thread (from signal handler) + * 3) any unmasked signal hitting the process + * 4) periodic ubf timer wakeups (after 3) + */ +static void +native_ppoll_sleep(rb_thread_t *th, rb_hrtime_t *rel) +{ + rb_native_mutex_lock(&th->interrupt_lock); + th->unblock.func = ubf_select; + th->unblock.arg = th; + rb_native_mutex_unlock(&th->interrupt_lock); + + GVL_UNLOCK_BEGIN(th); + if (!RUBY_VM_INTERRUPTED(th->ec)) { + struct pollfd pfd; + struct timespec ts; + + pfd.fd = signal_self_pipe.normal[0]; /* sigwait_fd */ + pfd.events = POLLIN; + (void)ppoll(&pfd, 1, rb_hrtime2timespec(&ts, rel), 0); + + /* + * do not read the fd, here, let uplevel callers or other threads + * that, otherwise we may steal and starve other threads + */ + } + unblock_function_clear(th); + unregister_ubf_list(th); + GVL_UNLOCK_END(th); +} + static void native_sleep(rb_thread_t *th, rb_hrtime_t *rel) { @@ -2020,6 +2057,9 @@ native_sleep(rb_thread_t *th, rb_hrtime_t *rel) rb_sigwait_fd_put(th, sigwait_fd); rb_sigwait_fd_migrate(th->vm); } + else if (th == th->vm->main_thread) { /* always able to handle signals */ + native_ppoll_sleep(th, rel); + } else { native_cond_sleep(th, rel); } |