pthread_join中的Segfault

Question

I have a fairly simple C code:

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

void* run(void *arg) {
  printf("hello from %d!\n", *(int*)arg);
  pthread_exit(NULL);
}

int main() {
  int ids[4];
  pthread_t threads[4];

  for (int i = 0; i < 4; i++) {
    ids[i] = i;
    printf("create thread %d\n", i);
    threads[i] = pthread_create(&threads[i], NULL, run, (void*)&ids[i]);
  }

  for (int i = 0; i < 4; i++) {
    printf("waiting for %d to join...\n", i);
    pthread_join(threads[i], NULL);
    printf("thread %d joined\n", i);
  }

  pthread_exit(NULL);
  return 0;
}

I compile it with

$ gcc -pthread -g -o main main.c

My output is

$ ./main                                                                                                                                                                    
create thread 0
create thread 1
create thread 2
create thread 3
waiting for 0 to join...
hello from 0!
zsh: segmentation fault (core dumped)  ./main

As you can see, it segfaults. gdb tells me nothing useful:

$ gdb ./main                                                                                                                                                                
GNU gdb (GDB) 7.11
Copyright (C) 2016 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./main...done.
(gdb) r
Starting program: /home/picard/projects/bme/pp-lab/sudoku/main 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
create thread 0
[New Thread 0x7ffff781a700 (LWP 9660)]
hello from 0!
create thread 1
[New Thread 0x7ffff7019700 (LWP 9661)]
create thread 2
hello from 1!
[New Thread 0x7ffff6818700 (LWP 9662)]
create thread 3
hello from 2!
[New Thread 0x7ffff6017700 (LWP 9663)]
hello from 3!
waiting for 0 to join...

Thread 1 "main" received signal SIGSEGV, Segmentation fault.
0x00007ffff7bc45e0 in pthread_join () from /usr/lib/libpthread.so.0
(gdb) bt
#0  0x00007ffff7bc45e0 in pthread_join () from /usr/lib/libpthread.so.0
#1  0x0000000000400786 in main () at main_old.c:22

Here is few info about my system:

$ gcc --version                                                                                                                                                             
gcc (GCC) 5.3.0
$ uname -a                                                                                                                                                                  
Linux enterprise 4.4.5-1-ARCH #1 SMP PREEMPT Thu Mar 10 07:38:19 CET 2016 x86_64 GNU/Linux

How should I continue to debug this problem?

Answer 1

pthread_create returns 0 on success, not the thread id, so

threads[i] = pthread_create(&threads[i], NULL, run, (void*)&ids[i]);

should be

if (pthread_create(&threads[i], NULL, run, (void*)&ids[i]))
{
  //take care of the error
}