Mail Archives: cygwin/2002/08/07/11:05:32
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I have a problem with signal delivery when using POSIX threads. If you
start 2 threads and sleep in both, but 1 has an alarm() defined, then
when the signal is delivered it also cancels the other thread.
My knowledge of pthreads is limited, so I don't know if this is an
expected result, but I tried the same program on Linux & Digital UNIX V4.0b
and got a different result.
Pseudo code:
thread 1
repeat
print message
sleep
thread 2
set alarm
sleep
exit
What I expected was that thread 1 would keep on running and not get any
signals
delivered, while thread 2 would just cancel the sleep and exit. However what
I got was that the sleep from thread 1 fails after the signal got delivered.
Included is the test case source. Following version numbers might be useful:
cygwin 1.3.12-4
gcc 3.1.1-4
On Windows 2000 SP1.
---- test case -----
#include <pthread.h>
#include <stdio.h>
#include <signal.h>
#include <time.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
pthread_mutex_t mux;
void *func(void *x)
{
int *p = (int *)x;
time_t t;
int r;
/* Print time every 5 seconds */
while(1) {
time(&t);
pthread_mutex_lock(&mux);
printf("thread %d - %s",*p,ctime(&t));
pthread_mutex_unlock(&mux);
r= sleep(5);
if (r) {
pthread_mutex_lock(&mux);
printf("Remaining %d\n", r);
pthread_mutex_unlock(&mux);
}
}
return NULL;
}
void *func2(void *x)
{
int *p = (int *)x;
time_t t;
/* Trigger SIGALRM after 7 seconds */
time(&t);
pthread_mutex_lock(&mux);
printf("thread %d - %s",*p,ctime(&t));
pthread_mutex_unlock(&mux);
alarm(7);
sleep(60*60);
alarm(0);
time(&t);
pthread_mutex_lock(&mux);
printf("exit thread %d - %s",*p,ctime(&t));
pthread_mutex_unlock(&mux);
return NULL;
}
void sighandler(int sig)
{
printf("Caught signal\n");
return;
}
int main()
{
pthread_t t;
pthread_t t2;
pthread_attr_t attr;
int i;
int p;
void *result;
struct sigaction actions;
memset((char *)&actions, 0, sizeof(actions));
sigemptyset(&actions.sa_mask);
actions.sa_flags = 0;
actions.sa_handler = sighandler;
sigaction(SIGALRM, &actions, NULL);
pthread_mutex_init(&mux, NULL);
pthread_mutex_lock(&mux);
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
i= 1;
if (pthread_create(&t, &attr, func, &i)!=0) {
perror("pthread_create t1");
}
p= 2;
if (pthread_create(&t2, &attr, func2, &p)!=0) {
perror("pthread_create t2");
}
printf("Main thread\n");
pthread_mutex_unlock(&mux);
pthread_join(t, &result);
pthread_join(t2, &result);
pthread_mutex_destroy(&mux);
return 0;
}
--------------------
Compile with:
gcc -o tester tester.c -lpthread
Output on cygwin:
$ ./tester
Main thread
thread 1 - Wed Aug 7 17:00:55 2002
thread 2 - Wed Aug 7 17:00:55 2002
thread 1 - Wed Aug 7 17:01:00 2002
exit thread 2 - Wed Aug 7 17:01:02 2002
Remaining 3
thread 1 - Wed Aug 7 17:01:02 2002
Remaining 5
thread 1 - Wed Aug 7 17:01:02 2002
Remaining 5
thread 1 - Wed Aug 7 17:01:02 2002
Remaining 5
thread 1 - Wed Aug 7 17:01:02 2002
Remaining 5
thread 1 - Wed Aug 7 17:01:02 2002
Output on Linux & Digital UNIX:
$ ./tester
Main thread
thread 1 - Wed Aug 7 17:00:02 2002
thread 2 - Wed Aug 7 17:00:02 2002
thread 1 - Wed Aug 7 17:00:07 2002
Caught signal
exit thread 2 - Wed Aug 7 17:00:09 2002
thread 1 - Wed Aug 7 17:00:12 2002
thread 1 - Wed Aug 7 17:00:17 2002
thread 1 - Wed Aug 7 17:00:22 2002
Am I making a gross mistake here?! Or is there a problem with cygwin?
Rgrds,
Karl Vogel
----------
Violence in reality is quite different from theory.
-- Spock, "The Cloud Minders", stardate 5818.4
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