pthread_join function crash - c

Question

There is a crash inside 'pthread_join' when main function calls it and before that the child thread already terminated. This is the backtrace from gdb:
Core was generated by `./bin/test'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0xb76fb530 in __call_tls_dtors#plt () from /lib/libpthread.so.0
(gdb) bt
#0 0xb76fb530 in __call_tls_dtors#plt () from /lib/libpthread.so.0
#1 0xb76fdd5a in start_thread (arg=0xb40fab40) at pthread_create.c:319
#2 0xb762f74e in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:129
The pthread activation function receives NULL argument and return NULL argument. I am clueless why I am seeing this crash consistently.
Could somebody help what could be wrong in child thread activation function? I am using Fedora 20 and gcc version 4.8.3 20140911 (Red Hat 4.8.3-7) (GCC)
Skeleton of child activation function is below
void* testControl(void* param)
{
...................
return NULL;
}
As the my code is huge I am giving here the code snippet which explains how I am creating child threads, their exits and termination.
unsigned long int rcThId1;
unsigned long int rcThId2;
unsigned long int rcThId3;
unsigned long int rcThId4;
unsigned long int rcThId5;
unsigned long int rcThId6;
void* rcControl1(void* arg)
{
bool th_loop = true;
while(th_loop)
{
/*Listen and receive the message on message queue*/
...........
..........
switch(message_type)
{
............
............
case EXIT:
th_loop = false;
break;
default:
break;
}
}
return NULL;
}
/*Activation functions for rcControl2 rcControl3 rcControl4
rcControl5 rcControl6 similar to the defination of rcControl1*/
int main(void)
{
pthread_create(&rcThId1,NULL,rcControl1,NULL);
pthread_create(&rcThId2,NULL,rcControl2,NULL);
pthread_create(&rcThId3,NULL,rcControl3,NULL);
pthread_create(&rcThId4,NULL,rcControl4,NULL);
pthread_create(&rcThId5,NULL,rcControl5,NULL);
pthread_create(&rcThId6,NULL,rcControl6,NULL);
..............
..............
/*Post EXIT event to Thread1*/
/*Post EXIT event to Thread2*/
/*Post EXIT event to Thread3*/
/*Post EXIT event to Thread4*/
/*Post EXIT event to Thread5*/
/*Post EXIT event to Thread6*/
/*By now all threads would have already exited */
pthread_join(rcThId1, NULL);/*Inside this function crash is happening*/
pthread_join(rcThId2, NULL);
pthread_join(rcThId3, NULL);
pthread_join(rcThId4, NULL);
pthread_join(rcThId5, NULL);
pthread_join(rcThId6, NULL);
return 0;
}
Inside pthread_join(rcThId1, NULL); call the crash is happened.
Thanks

Answer 1

In the (pseudo)code you posted, the main issue is the type of thread identifiers: they all should be of type pthread_t. But you have unsigned long ints. The crash is most likely because pthread_join() attempts to read rcThId1 et al as if they are pthread_t which they are not.
Change the type of rcThId1 ..rcThId6 to pthread_t.
You should be getting some warnings. If not compiler with:
gcc -Wall -Wextra -pedantic-errors
Aside:
You probably need to have th thread ids as global. Move them inside main() unless you have a good reason not to.