Date: Mon, 19 Oct 1998 11:30:17 -0700 (PDT) From: info@highwind.com To: freebsd-gnats-submit@FreeBSD.ORG Subject: kern/8375: pthread_cond_wait() spins the CPU Message-ID: <199810191830.LAA03985@hub.freebsd.org>
next in thread | raw e-mail | index | archive | help
>Number: 8375
>Category: kern
>Synopsis: pthread_cond_wait() spins the CPU
>Confidential: no
>Severity: serious
>Priority: high
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Mon Oct 19 11:40:00 PDT 1998
>Last-Modified:
>Originator: Robert Fleischman
>Organization:
HighWind Software, Inc.
>Release: 3.0 with LATEST libc_r
>Environment:
% uname -a
FreeBSD zonda.highwind.com 3.0-19980831-SNAP FreeBSD 3.0-19980831-SNAP #0: Mon Aug 31 14:03:19 GMT 1998 root@make.ican.net:/usr/src/sys/compile/GENERIC i386
>Description:
If a number of threads are waiting for a condition, the application spins
the CPU at 100% and eventually hangs the application. I've included
a test program below which illustrates the problem.
>How-To-Repeat:
/* Illustration of FreeBSD pthread_cond_wait() bug
This program sets up a conditional wait and fires off a dozen threads
that simply wait for the condition. Once the threads are started,
the main thread loops signalling the condition once a second.
Normally, this should result in "Signalling" and "Got Condition"
being printed once a second. However, because of some bugs in
FreeBSD, the pthread_cond_wait() spins the CPU and no progress is
made.
g++ -o condWaitBug -D_REENTRANT -D_THREAD_SAFE -g -Wall condWaitBug.C -pthread
*/
#include <assert.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
pthread_mutex_t lock;
pthread_cond_t condition;
static void *condThread(void *)
{
// Wait until we are signalled, then print.
while (true) {
assert(!::pthread_cond_wait(&condition, &lock));
::printf("Got Condition!\n");
}
}
int main(int, char **)
{
// Initialize Lock
pthread_mutexattr_t lock_attr;
assert(!::pthread_mutexattr_init(&lock_attr));
assert(!::pthread_mutex_init(&lock, &lock_attr));
assert(!::pthread_mutexattr_destroy(&lock_attr));
// Initialize Condition
pthread_condattr_t cond_attr;
assert(!::pthread_condattr_init(&cond_attr));
assert(!::pthread_cond_init(&condition, &cond_attr));
assert(!::pthread_condattr_destroy(&cond_attr));
// Lock the lock
assert(!::pthread_mutex_lock(&lock));
// Spawn off a dozen threads to get signalled
for (int j = 0; j < 12; ++j) {
pthread_t tid;
pthread_attr_t attr;
assert(!::pthread_attr_init(&attr));
assert(!::pthread_create(&tid, &attr, condThread, 0));
assert(!::pthread_attr_destroy(&attr));
}
// Sleep for 3 seconds to make sure the threads started up.
timeval timeout;
timeout.tv_sec = 3;
timeout.tv_usec = 0;
::select(0, 0, 0, 0, &timeout);
for (int k = 0; k < 60; ++k) {
::printf("Signalling\n");
::pthread_cond_signal(&condition);
// Sleep for a second
timeout.tv_sec = 1;
timeout.tv_usec = 0;
::select(0, 0, 0, 0, &timeout);
}
return EXIT_SUCCESS;
}
>Fix:
>Audit-Trail:
>Unformatted:
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-bugs" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199810191830.LAA03985>