6. Parallel Implementation - wait for first using pipe

pthread_pipe.c:

// run a function in parallel N times, wait for the first one to finish
//
// using a pipe for thread communication
//
// run time is minimum of the run times for each function call
//
#include <string.h>
#include <pthread.h>

#include "common.c"

 // to avoid stdio buffering on the pipe, must make stdout unbuffered
 // or do fflush(stdout) after every printf()
 //
  setbuf( stdout, 0); // make stdout unbuffered

 // redirect stdin and stdout through pipe
 //
  int fd[2]; if( pipe(fd)) { perror("pipe"); return 1; }

  dup2(fd[0],0); dup2(fd[1],1); close(fd[0]); close(fd[1]);

 // start the threads
 //
  pthread_t t[N];

  for( int i = 0; i < N; ++i)
    if( pthread_create( &t[i], 0, f, &D[i].i ) ) { perror( "pthread_create"); return 1; }

 // wait until any one thread is finished
 //
  char msg[BUFSIZ];

  while( fgets( msg, BUFSIZ, stdin) )
  {
    fputs( msg, stderr); // copy thread messages to stderr

    if( strstr( msg, "done") ) break;
  }

 // stop all threads
 //
  for( int i = 0; i < N; ++i) pthread_cancel( t[i]);
}
---
$ gcc -std=c11 -pedantic -Wall -g -O -o pthread_pipe pthread_pipe.c -pthread
$ time ./pthread_pipe
f 0 start = 0, size = 6
f 1 start = 10, size = 5
f 3 start = 30, size = 3
f 2 start = 20, size = 4
f 3 done

real	0m3.004s
user	0m0.003s
sys	0m0.002s