Date: Mon, 19 Oct 1998 14:35:40 -0400 (EDT) From: HighWind Software Information <info@highwind.com> To: current@FreeBSD.ORG Subject: Another Serious libc_r problem Message-ID: <199810191835.OAA20137@highwind.com>
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We found another libc_r problem which is spinning the CPU at 100%.
This makes it impossible for our application to work at all.
FreeBSD 3.0 kernel from August. The LATEST libc_r. Tested this on
another FreeBSD with a much more recent kernel. Same result. The CPU
spins and the threads don't get the condition.
Program works fine on other operating systems. After the 3 second
start up, it prints nice stream of "Signalling" and "Got Condition!".
On FreeBSD 3.0, it prints "Signalling" twice and then spins the CPU.
Help is always appreciated.
-Rob
---
/* 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;
}
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