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thread_pthread.c: hoist out do_gvl_timer and improve documentation

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This hopefully clarifies the roles of UBF_TIMER and vm->gvl.timer

[ruby-core:88475] [Misc #14937]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64377 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
This commit is contained in:
normal 2018-08-15 07:16:55 +00:00
parent 727a2d55a3
commit 4610d36c4c
1 changed files with 58 additions and 29 deletions
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87
thread_pthread.c
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@ -43,11 +43,28 @@
/*
* UBF_TIMER and ubf_list both use SIGVTALRM.
* UBF_TIMER is to close TOCTTOU signal race on programs
* without GVL contention blocking read/write to sockets.
*
* ubf_list wakeups may be triggered periodically by UBF_TIMER on
* gvl_yield.
* UBF_TIMER has NOTHING to do with thread timeslices (TIMER_INTERRUPT_MASK)
*
* UBF_TIMER is to close TOCTTOU signal race on programs where we
* cannot rely on GVL contention (vm->gvl.timer) to perform wakeups
* while a thread is doing blocking I/O on sockets or pipes. With
* rb_thread_call_without_gvl and similar functions:
*
* (1) Check interrupts.
* (2) release GVL.
* (2a) signal received
* (3) call func with data1 (blocks for a long time without ubf_timer)
* (4) acquire GVL.
* Other Ruby threads can not run in parallel any more.
* (5) Check interrupts.
*
* We need UBF_TIMER to break out of (3) if (2a) happens.
*
* ubf_list wakeups may be triggered on gvl_yield.
*
* If we have vm->gvl.timer (on GVL contention), we don't need UBF_TIMER
* as it can perform the same tasks while doing timeslices.
*/
#define UBF_TIMER_NONE 0
#define UBF_TIMER_POSIX 1
@ -154,6 +171,37 @@ designate_timer_thread(rb_vm_t *vm)
return FALSE;
}
/*
* We become designated timer thread to kick vm->gvl.acquired
* periodically. Continue on old timeout if it expired.
*/
static void
do_gvl_timer(rb_vm_t *vm, rb_thread_t *th)
{
static struct timespec ts;
static int err = ETIMEDOUT;
native_thread_data_t *nd = &th->native_thread_data;
/* take over wakeups from UBF_TIMER */
ubf_timer_disarm();
if (err == ETIMEDOUT) {
ts.tv_sec = 0;
ts.tv_nsec = TIME_QUANTUM_NSEC;
ts = native_cond_timeout(&nd->cond.gvlq, ts);
}
vm->gvl.timer = th;
err = native_cond_timedwait(&nd->cond.gvlq, &vm->gvl.lock, &ts);
vm->gvl.timer = 0;
ubf_wakeup_all_threads();
/*
* Timeslice. Warning: the process may fork while this
* thread is contending for GVL:
*/
if (vm->gvl.acquired) timer_thread_function();
}
static void
gvl_acquire_common(rb_vm_t *vm, rb_thread_t *th)
{
@ -164,33 +212,10 @@ gvl_acquire_common(rb_vm_t *vm, rb_thread_t *th)
"we must not be in ubf_list and GVL waitq at the same time");
list_add_tail(&vm->gvl.waitq, &nd->node.gvl);
do {
if (!vm->gvl.timer) {
static struct timespec ts;
static int err = ETIMEDOUT;
/* take over wakeups from UBF_TIMER */
ubf_timer_disarm();
/*
* become designated timer thread to kick vm->gvl.acquired
* periodically. Continue on old timeout if it expired:
*/
if (err == ETIMEDOUT) {
ts.tv_sec = 0;
ts.tv_nsec = TIME_QUANTUM_NSEC;
ts = native_cond_timeout(&nd->cond.gvlq, ts);
}
vm->gvl.timer = th;
err = native_cond_timedwait(&nd->cond.gvlq, &vm->gvl.lock, &ts);
vm->gvl.timer = 0;
ubf_wakeup_all_threads();
/*
* Timeslice. Warning: the process may fork while this
* thread is contending for GVL:
*/
if (vm->gvl.acquired) timer_thread_function();
do_gvl_timer(vm, th);
}
else {
rb_native_cond_wait(&nd->cond.gvlq, &vm->gvl.lock);
@ -1368,6 +1393,10 @@ rb_thread_wakeup_timer_thread_fd(int fd)
}
}
/*
* This ensures we get a SIGVTALRM in TIME_QUANTUM_MSEC if our
* process could not react to the original signal in time.
*/
static void
ubf_timer_arm(rb_pid_t current) /* async signal safe */
{