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Old 03-09-2004, 10:38 PM   #1
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My thread hangs while writting into a file

Hi guys,

I have a multithreaded program. One of the thread suddenly hangs for for ever. I tried using strace -p to see where exactly it is hanging. Here is the tail of that file

write(4, "Mar 9 16:46:51.893 [14318] [EXT"..., 102) = 102
time(NULL) = 1078865211
write(3, "1078865211: 356510: checking hea"..., 34) = 34
time(NULL) = 1078865211
write(3, "1078865211: 356510: *** alloc: a"..., 83) = 83
time(NULL) = 1078865211
write(3, "1078865211: 356511: checking hea"..., 34) = 34
time(NULL) = 1078865211
write(3, "1078865211: 356511: *** alloc: a"..., 103) = 103
time(NULL) = 1078865211
write(3, "1078865211: 356512: checking hea"..., 34) = 34
time(NULL) = 1078865211
write(3, "1078865211: 356512: *** alloc: a"..., 103) = 103
rt_sigprocmask(SIG_SETMASK, NULL, [RTMIN], 8) = 0

any idea why this sigsuspend is getting called soon after thread tries to write on fd=3. After this call my thread waits for the signal for for ever. I am not sure, which signal it is.
My process is deamon so stdin/stdout/err is closed.

I have compiled dmalloc library with my program and during this run dmalloc is active by setting DMALLOC_OPTIONS env variable.

Thanks in advance for your response.


Last edited by skdevnath; 03-09-2004 at 10:41 PM.
Old 03-10-2004, 10:43 AM   #2
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Are you using fork() or pthreads or what? If you're using a wait() or waitpid() function it might do a suspend. Can you paste the code?
Old 03-11-2004, 05:13 PM   #3
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I was using pthread.

Looks like I found the problem.
The problem what I think is
1). thread1 is about to lock a mutex but at the same time it got schduled out.
2). thread2 frees the c++ object containing the same mutex. The thread's code gets the same mutex lock before deleting the object.
3). Now when thread1 again gets scheduled, it tries to lock the deleted object's mutex and so it waits for ever since the destructor for the object never unlocks the mutex. However it calls pthread_mutex_destroy () on the mutex.
4). Now since that object is deleted for ever and object is unreferenced so thread2 or anybody else never call unlock for same mutex.

Note: My object's destructor calls pthread_mutex_destroy () on same mutes.

So there are little unexplain things are there but I dont like the idea of triying to aquire a lock on deleted object. I solved this problem by puting mutex out of the object at global level. This solution worked for me now.


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