CODEWITHSUNDEEP
cmultithreadingpthreads
Lorin
Lorin

Reputation: 341

Created thread is slow

I encoutered a weird behavior of pthread_create function. The code follows:

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

void *foo( void* a) {
    printf("Doing something");
    pthread_exit(NULL);
}

int main() {
    printf("Main created");
    pthread_t thread;
    pthread_create( &thread, NULL, foo, NULL );

    while(1); // This causes trouble

    pthread_join( thread, NULL );

    return 0;
}

For some reason, with the while in place, message from thread is showed after a really long delay. I would expect that after pthread_create call new thread is completely independent from main and thus should not be afected by its code.

Upvotes: 0

Views: 306

Answers (1)

user149341
user149341

Reputation:

This has nothing to do with threads.

You'll find that the same behavior occurs with:

printf("Doing something");
while(1) ;

This is because you didn't include a newline on the end of the string you printed, which causes the line to be buffered. Since no further output is generated, the line may be buffered for a very long time (possibly even forever).

To avoid this, you can either:

  • Add newlines to all of your output lines, e.g. printf("Doing something\n");

  • Call fflush(stdout) after printf() to force the line to be flushed

  • Call setvbuf(stdout, NULL, _IONBF, 0) beforehand to disable all output buffering

Upvotes: 3

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