njamd shows leaks with pthreads

shy · 12-24-2004, 01:56 AM

Hi.

Manpage for pthread_join() says

Quote:

When a joinable thread terminates, its memory resources
(thread descriptor and stack) are not deallocated until
another thread performs pthread_join on it. Therefore,
pthread_join must be called once for each joinable thread
created to avoid memory leaks.

However, I found that it does not deallocate the resources, at least in njamd's opinion (but I personally do beleive njamd). Does anyone know what it the reason and how to force the freeing?

The program:

Code:

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>

static void * test_thread (void * arg)
{
        printf ("thread started\n");
        pthread_exit(NULL);
}

int main (void)
{
        pthread_t thread_id;
        void * ptr;
        if (pthread_create (&thread_id, NULL, test_thread, NULL))
                goto thread_fail;
        pthread_join (thread_id, &ptr);
        printf ("good bye\n");
        return 0;

thread_fail:
        printf ("failed!!!\n");
        return 1;
}

That's how I run it:

Code:

LD_PRELOAD=libnjamd.so NJAMD_PROT=strict NJAMD_DUMP_LEAKS_ON_EXIT=3 ./a.out

And this is it's output:

Code:

thread started
good bye

0x4213c000-0x4213e000: Aligned len 68
   Allocation callstack:
        called from ./a.out(pthread_join+0x12e)[0x80484e2]
        called from /lib/tls/libc.so.6(__libc_start_main+0xe4)[0x420157a4]
        called from ./a.out(pthread_join+0x41)[0x80483f5]
   Not Freed

NJAMD totals:

        Allocation totals:              1 total, 1 leaked
        Leaked User Memory:             68 bytes
        Peak User Memory:               68 bytes
        NJAMD Overhead at peak:         7.934 kB
        Peak NJAMD Overhead:            7.934 kB
        Average NJAMD Overhead:         7.934 kB per alloc
        Address space used:             8.000 kB
        NJAMD Overhead at exit:         7.934 kB

shishir · 12-24-2004, 03:55 AM

i guess it would be because of the manager thread that would be getting cleared after the main returns or calls exit.,..

shy · 12-24-2004, 04:22 AM

Well, it's obvious that exit() clears all the memory allocated by an application. But if you run an application that should run for a long time, and start/stop threads, eventually your application will eat all the available memory.
I would like to free all the allocation memory during the work of my program, not after it ends.

shishir · 12-24-2004, 04:46 AM

what i am trying to say is memory is not being leaked as such...but maybe njamd is not being able to capture that piece of code and hence calls it a leak....if you see...try doing a malloc from a thread and free it...even then you'd see only one leak and two allocations.....if you are freeing all the memory that you have allocated..then you'd be fine...as you''ll see that 'your" threads arent leaking any memory...

i couild be wrong..but this is what i feel...it is just that the njamd might not be doing any check on the manager thread..and that is the memory i see getting "leaked"..it is the same amount of memory leaking no matter how many threads i run ...have you tried doing the same thing on 2.6 kernel? or on solaris perhaps...they dont have manager threads...maybe you'll get no leaks...

shy · 12-24-2004, 05:52 AM

Thank you, I've checked, and it seems that only manager's memory leaks (because 68 leaked bytes don't depend on how many threads do I start).

Actually, I tested it on 2.6 kernel, but the kernel version alone isn't the case. I have old glibc without NPTL, so I get a manager thread and this leak.

shishir · 12-24-2004, 07:07 AM

yeah you are right...nptl and glibc would be imp. and i am not sure that it is supported by 2.4 series..