From d2afeb9445a3dc8445fa48f601a78c5ecd743ca6 Mon Sep 17 00:00:00 2001
From: normal <normal@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 19 Aug 2018 00:01:08 +0000
Subject: thread_pthread.c: reset timeslice delay when uncontended

This matches the behavior of old timer thread more closely
and seems to fix [Bug #14999] when limited to a single CPU.
I cannot reproduce the error on a multi-core system unless
I use schedtool to force affinity to a single CPU:

schedtool -a 0x01 -e make test-spec \
	MSPECOPT='-R1000 spec/ruby/library/conditionvariable/wait_spec.rb'

While it may be good enough to pass the spec, I don't have
huge degree of confidence in the interrupt handling robustness
under extremely heavy load (these may be ancient bugs, though).

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@64467 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 thread_pthread.c | 9 ++++++---
 thread_pthread.h | 1 +
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/thread_pthread.c b/thread_pthread.c
index af933d4a15..2fd60ddd4a 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -180,19 +180,18 @@ 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) {
+    if (vm->gvl.timer_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_err = native_cond_timedwait(&nd->cond.gvlq, &vm->gvl.lock, &ts);
     vm->gvl.timer = 0;
 
     ubf_wakeup_all_threads();
@@ -244,6 +243,9 @@ gvl_acquire_common(rb_vm_t *vm, rb_thread_t *th)
             rb_native_cond_signal(&vm->gvl.switch_cond);
         }
     }
+    else { /* reset timer if uncontended */
+        vm->gvl.timer_err = ETIMEDOUT;
+    }
     vm->gvl.acquired = th;
     if (!vm->gvl.timer) {
         if (!designate_timer_thread(vm) && !ubf_threads_empty()) {
@@ -325,6 +327,7 @@ gvl_init(rb_vm_t *vm)
     list_head_init(&vm->gvl.waitq);
     vm->gvl.acquired = 0;
     vm->gvl.timer = 0;
+    vm->gvl.timer_err = ETIMEDOUT;
     vm->gvl.need_yield = 0;
     vm->gvl.wait_yield = 0;
 }
diff --git a/thread_pthread.h b/thread_pthread.h
index 8fb1d521b6..c64018bb13 100644
--- a/thread_pthread.h
+++ b/thread_pthread.h
@@ -53,6 +53,7 @@ typedef struct rb_global_vm_lock_struct {
     /* slow path */
     struct list_head waitq;
     const struct rb_thread_struct *timer;
+    int timer_err;
 
     /* yield */
     rb_nativethread_cond_t switch_cond;
-- 
cgit v1.2.1