Date: Mon, 1 Nov 2004 18:25:36 GMT From: Thomas Ludwig <tludwig@smr.ch> To: freebsd-gnats-submit@FreeBSD.org Subject: misc/73387: manpage of pthread_mutex_lock does not mention EBUSY (libpthread) Message-ID: <200411011825.iA1IPads036140@www.freebsd.org> Resent-Message-ID: <200411011830.iA1IUcQP049939@freefall.freebsd.org>
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>Number: 73387
>Category: misc
>Synopsis: manpage of pthread_mutex_lock does not mention EBUSY (libpthread)
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Mon Nov 01 18:30:38 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator: Thomas Ludwig
>Release: RELENG_5
>Organization:
SMR Engineering & Development
>Environment:
FreeBSD pingu.smr-internal.ch 5.3-STABLE FreeBSD 5.3-STABLE #1: Mon Nov 1 18:19:35 CET 2004 root@pingu.smr-internal.ch:/usr/obj/usr/src/sys/PINGU i386
>Description:
The manpage of pthread_mutex_lock mentions EINVAL and EDEADLK as possible error codes, but not EBUSY. However, threads not owning the mutex will get EBUSY when compiled with -lpthread:
from src/lib/libpthread/thread/thr_mutex.c:
/* case PTHREAD_MUTEX_DEFAULT: */
case PTHREAD_MUTEX_ERRORCHECK:
case PTHREAD_MUTEX_NORMAL:
/*
* POSIX specifies that mutexes should return EDEADLK if a
* recursive lock is detected.
*/
if (m->m_owner == curthread)
ret = EDEADLK;
else
ret = EBUSY;
break;
>How-To-Repeat:
Compile and execute the following program:
#include <sys/types.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
pthread_mutex_t mutex;
void
trylock(const char* tname)
{
int rc;
rc = pthread_mutex_trylock(&mutex);
if (rc != 0)
fprintf(stderr, "%s: Could not lock mutex again: %s\n",
tname, strerror(rc));
else {
fprintf(stderr, "Could lock mutex again!");
exit(1);
}
}
void*
start(void* data)
{
/* try to lock the mutex again */
trylock("Second thread");
}
int
main(int argc, const char* argv[])
{
pthread_t thread;
int rc;
/* create a mutex and acquire a lock on it for the main thread */
if (pthread_mutex_init(&mutex, NULL) != 0) {
perror("Could not initialize mutex");
exit(1);
}
if (pthread_mutex_lock(&mutex) != 0) {
perror("Could not lock mutex");
exit(1);
}
/* spawn a second thread */
if (pthread_create(&thread, NULL, start, NULL) != 0) {
perror("Could not create thread");
exit(1);
}
/* try to lock the mutex again */
trylock("Main thread");
if (pthread_join(thread, NULL) != 0) {
perror("Could not join threads");
exit(1);
}
exit(0);
}
>Fix:
Something like this:
--- /usr/src/share/man/man3/pthread_mutex_lock.3 Thu Jan 15 16:59:00 2004
+++ /tmp/pthread_mutex_lock.3 Mon Nov 1 19:19:54 2004
@@ -62,8 +62,11 @@
The value specified by
.Fa mutex
is invalid.
+.It Bq Er EBUSY
+.Fa mutex
+is locked by another thread.
.It Bq Er EDEADLK
-A deadlock would occur if the thread blocked waiting for
+Attempt to recursively lock
.Fa mutex .
.El
.Sh SEE ALSO
>Release-Note:
>Audit-Trail:
>Unformatted:
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