Date: Fri, 27 Nov 1998 21:20:59 -0800 (PST) From: Jason Evans <jasone@canonware.com> To: FreeBSD-gnats-submit@FreeBSD.ORG Subject: bin/8872: pthread_cond_timedwait() can cause lost pthread_cond_signal() Message-ID: <Pine.BSF.4.05.9811272118380.774-100000@sturm.canonware.com>
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>Number: 8872
>Category: bin
>Synopsis: pthread_cond_timedwait() can cause lost pthread_cond_signal()
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Fri Nov 27 21:30:00 PST 1998
>Last-Modified:
>Originator: Jason Evans
>Organization:
>Release: FreeBSD 2.2.7-STABLE i386
>Environment:
FreeBSD orkan 2.2.7-STABLE FreeBSD 2.2.7-STABLE #0:
Thu Nov 26 09:13:44 PST 1998
toor@orkan:/usr/src/sys/compile/CRASH_orkan i386
>Description:
pthread_cond_timedwait() causes a thread to be unscheduled for a specified
period of time, unless a condition becomes true. If that timeout expires, the
thread is rescheduled, but it is left on the condition wait queue. This can
cause a pthread_cond_signal() to be lost.
>How-To-Repeat:
1) Call pthread_cond_timedwait() in thread A.
2) Let the timer expire.
3) Call pthread_cond_wait() in thread B.
4) Call pthread_cond_signal() in thread A.
*** The signal will have no effect.
5) Call pthread_cond_signal() again in thread A.
*** Thread B will be signaled.
>Fix:
It looks safe to ignore the return value of _thread_queue_remove(), but I
may be mistaken.
--- Begin patch -------------------------------------------------------------
*** /usr/src/lib/libc_r/uthread/uthread_kern.c.orig Fri Nov 27 16:10:16 1998
--- /usr/src/lib/libc_r/uthread/uthread_kern.c Fri Nov 27 16:05:16 1998
***************
*** 171,176 ****
--- 171,185 ----
FD_ZERO(&pthread->data.select_da
ta->writefds);
FD_ZERO(&pthread->data.select_da
ta->exceptfds);
pthread->data.select_data->nfds
= 0;
+ } else if (pthread->state == PS_COND_WAI
T) {
+ /*
+ * The pthread_cond_timedwait()
+ * has timed out, so remove the
+ * thread from the condition's
+ * queue.
+ */
+ _thread_queue_remove(pthread->qu
eue,
+ pthread);
}
/*
--- End patch ---------------------------------------------------------------
>Audit-Trail:
>Unformatted:
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