Thanks for your reply.
>-----Original Message-----
>From: Peter Zijlstra [mailto:pet...@infradead.org]
>Sent: Monday, June 23, 2014 5:13 PM
>To: Tony Lu
>Cc: Paul Mackerras; Ingo Molnar; Arnaldo Carvalho de Melo;
>linux-kernel@vger.kernel.org; Chris Metcalf
>Subject: Re: [BUG] perf: can not resolve symbols for forked threads
>
>On Thu, Jun 19, 2014 at 07:39:42AM +0000, Tony Lu wrote:
>> Hi
>>
>> I got the below output that shows perf can not resolve symbols for
>> forked threads. I did a system-wide collection from all CPUs after the
>> application hello run.
>
>There's no fork() in... :-)
Yes, but perf regards pthread_created threads as forked threads, and a
PERF_RECORD_FORK event will be delivered when a thread is forked or cloned.
>
>> #include <pthread.h>
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <unistd.h>
>> #define NUM_THREADS 5
>>
>> void foo(void)
>> {
>> long i = 1000000000;
>> while (i--) {
>> ;
>> }
>> }
>>
>> void *PrintHello(void *threadid)
>> {
>> long tid;
>> tid = (long)threadid;
>> printf("Hello World! It's me, thread #%ld!\n", tid);
>> foo();
>> pthread_exit(NULL);
>> }
>>
>> int main(int argc, char *argv[])
>> {
>> pthread_t threads[NUM_THREADS];
>> int rc;
>> long t;
>> for(t=0;t<NUM_THREADS;t++){
>> printf("In main: creating thread %ld\n", t);
>> rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
>> if (rc){
>> printf("ERROR; return code from pthread_create() is %d\n", rc);
>> exit(-1);
>> }
>> }
>>
>> /* Last thing that main() should do */
>> pthread_exit(NULL);
>> }
>
>That pthread_exit() is the problem; this results in:
>
>29456 pts/23 Zl 0:00 | \_ [hello] <defunct>
>
>You want to wait for the threads to complete using pthread_join().
>
>I suspect the defunct state hides the process.
Yes, using pthread_join() can workaround this problem.
Does that mean the parent thread can not exit before the child threads? It
still seems like a perf bug.
-Thanks
-Tony
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