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Subject[PATCH] sigtimedwait with zero timeout should not block
As I mentioned earlier sigtimedwait with a zero timeout (0,0) should not
block, but it currently does for 10msec (one jiffie). This is a
performance problem for applications using polled signal queues. SUSV2
says specifically for this case "returns immediately with an error".

Attached is a new version of my patch. The previous version messed up
the signal mask if the signal queue was empty and a zero timeout was
selected.

It is still waiting one more jiffie than what is indicated by the
timeout value if other than zero, caused by the following code fragment:

timeout = (timespec_to_jiffies(&ts)
+ (ts.tv_sec || ts.tv_nsec));

Does anyone have any clue on why this +1 is there? I think this should
also go away to only read

timeout = timespec_to_jiffies(&ts);

--
Henrik Nordstrom
--- linux-2.4.0-test8/kernel/signal.c Fri Sep 22 11:11:05 2000
+++ linux-2.4.0-test8-reiserfs-3.6.15-raw-20000915-hno/kernel/signal.c Fri Sep 22 11:08:29 2000
@@ -939,25 +939,28 @@
spin_lock_irq(&current->sigmask_lock);
sig = dequeue_signal(&these, &info);
if (!sig) {
- /* None ready -- temporarily unblock those we're interested
- in so that we'll be awakened when they arrive. */
- sigset_t oldblocked = current->blocked;
- sigandsets(&current->blocked, &current->blocked, &these);
- recalc_sigpending(current);
- spin_unlock_irq(&current->sigmask_lock);
-
timeout = MAX_SCHEDULE_TIMEOUT;
if (uts)
timeout = (timespec_to_jiffies(&ts)
+ (ts.tv_sec || ts.tv_nsec));

- current->state = TASK_INTERRUPTIBLE;
- timeout = schedule_timeout(timeout);
+ if (timeout) {
+ /* None ready -- temporarily unblock those we're
+ * interested while we are sleeping in so that we'll
+ * be awakened when they arrive. */
+ sigset_t oldblocked = current->blocked;
+ sigandsets(&current->blocked, &current->blocked, &these);
+ recalc_sigpending(current);
+ spin_unlock_irq(&current->sigmask_lock);
+
+ current->state = TASK_INTERRUPTIBLE;
+ timeout = schedule_timeout(timeout);

- spin_lock_irq(&current->sigmask_lock);
- sig = dequeue_signal(&these, &info);
- current->blocked = oldblocked;
- recalc_sigpending(current);
+ spin_lock_irq(&current->sigmask_lock);
+ sig = dequeue_signal(&these, &info);
+ current->blocked = oldblocked;
+ recalc_sigpending(current);
+ }
}
spin_unlock_irq(&current->sigmask_lock);
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