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* exceptions.cc (_cygtls::handle_SIGCONT): Simplify loop waiting for 

sig_handle_tty_stop to wake up.  Make sure to unlock before calling
	yield to avoid starvation of sig_handle_tty_stop.  Add comments.
	* miscfuncs.cc (yield): Explain why yield should never be called under
	_cygtls::lock conditions.  Call SleepEx with 1ms timeout.  Explain why.
This commit is contained in:
Corinna Vinschen 2013-06-06 15:29:41 +00:00
parent 925e1c8157
commit b3f0fb6baa
3 changed files with 30 additions and 23 deletions
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8
winsup/cygwin/ChangeLog
View File

@ -1,3 +1,11 @@
2013-06-06 Corinna Vinschen <corinna@vinschen.de>
* exceptions.cc (_cygtls::handle_SIGCONT): Simplify loop waiting for
sig_handle_tty_stop to wake up. Make sure to unlock before calling
yield to avoid starvation of sig_handle_tty_stop. Add comments.
* miscfuncs.cc (yield): Explain why yield should never be called under
_cygtls::lock conditions. Call SleepEx with 1ms timeout. Explain why.
2013-06-05 Corinna Vinschen <corinna@vinschen.de>
* include/cygwin/version.h (CYGWIN_VERSION_DLL_MINOR): Bump to 20.

27
winsup/cygwin/exceptions.cc
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@ -1253,25 +1253,18 @@ _cygtls::handle_SIGCONT ()
{
myself->stopsig = 0;
myself->process_state &= ~PID_STOPPED;
int state = 0;
/* Carefully tell sig_handle_tty_stop to wake up. */
while (state < 2)
{
lock ();
if (sig)
yield (); /* state <= 1 */
else if (state)
state++; /* state == 2 */
else
{
sig = SIGCONT;
SetEvent (signal_arrived);
state++; /* state == 1 */
}
unlock ();
}
lock ();
sig = SIGCONT;
SetEvent (signal_arrived);
/* Make sure yield doesn't run under lock condition to avoid
starvation of sig_handle_tty_stop. */
unlock ();
/* Wait until sig_handle_tty_stop woke up. */
while (sig)
yield ();
/* Tell wait_sig to handle any queued signals now that we're alive
again. */
again. */
sig_dispatch_pending (false);
}
/* Clear pending stop signals */

18
winsup/cygwin/miscfuncs.cc
View File

@ -236,7 +236,11 @@ check_iovec (const struct iovec *iov, int iovcnt, bool forwrite)
return (ssize_t) tot;
}
/* Try hard to schedule another thread. */
/* Try hard to schedule another thread.
Note: Don't call yield under _cygtls::lock conditions. It results in
potential starvation, especially on a single-CPU system, because
_cygtls::lock also calls yield when waiting for the lock. */
void
yield ()
{
@ -244,11 +248,13 @@ yield ()
SetThreadPriority (GetCurrentThread (), THREAD_PRIORITY_IDLE);
for (int i = 0; i < 2; i++)
{
/* MSDN implies that SleepEx(0,...) will force scheduling of other
threads. Unlike SwitchToThread() the documentation does not mention
other cpus so, presumably (hah!), this + using a lower priority will
stall this thread temporarily and cause another to run. */
SleepEx (0, false);
/* MSDN implies that SleepEx will force scheduling of other threads.
Unlike SwitchToThread() the documentation does not mention other
cpus so, presumably (hah!), this + using a lower priority will
stall this thread temporarily and cause another to run.
Note: Don't use 0 timeout. This takes a lot of CPU if something
goes wrong. */
SleepEx (1L, false);
}
SetThreadPriority (GetCurrentThread (), prio);
}