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Date: Wed, 24 May 2006 18:14:11 -0400
From: Kurt Miller <lists@intricatesoftware.com>
To: freebsd-threads@freebsd.org
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Subject: pthread_cond_signal w/suspended threads
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I've been working on an intermittent deadlock in
the jvm and have isolated it to the following issue.
When multiple threads are waiting on a condition
variable and some of those threads have been suspended
with pthread_suspend_np(), there is an expectation that
pthread_cond_signal() will signal an unsuspended thread
first. However, the following program shows this is not
the case on 6.1-release/kse (thr works as expected).

Can kse behavior be changed to signal unsuspended
threads first?

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <pthread_np.h>

pthread_cond_t  cond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

static void *
start_routine(void *arg)
{
    pthread_mutex_lock(&mutex);
    pthread_cond_wait(&cond, &mutex);
    printf("unblocked %d\n", (int)arg);
    pthread_mutex_unlock(&mutex);
    return (0);
}

int
main(int argc, char *argv[])
{
    pthread_t thread1;
    pthread_t thread2;

    pthread_create(&thread1, NULL, start_routine, (void *)1);
    sleep(1);
    pthread_create(&thread2, NULL, start_routine, (void *)2);
    sleep(1);
    pthread_suspend_np(thread1);
    pthread_cond_signal(&cond);
    sleep(1);
    pthread_resume_np(thread1);
    sleep(1);
    return (0);
}