多个 fork() 并发 [英] Multiple fork() Concurrency

问题描述

How do you use the fork() command in such a way that you can spawn 10 processes and have them do a small task concurrently.

Concurrent is the operative word, many places that show how to use fork only use one call to fork() in their demos. I thought you would use some kind of for loop but i tried and it seems in my tests that the fork()'s are spawning a new process, doing work, then spawning a new process. So they appear to be running sequentially but how can I fork concurrently and have 10 processes do the work simultaneously if that makes sense?

Thanks.

Update: Thanks for the answers guys, I think I just misunderstood some aspects of fork() initially but i understand it now. Cheers.

解决方案

Call fork() in a loop:

Adding code to wait for children per comments:

int numberOfChildren = 10;
pid_t *childPids = NULL;
pid_t p;

/* Allocate array of child PIDs: error handling omitted for brevity */
childPids = malloc(numberOfChildren * sizeof(pid_t));

/* Start up children */
for (int ii = 0; ii < numberOfChildren; ++ii) {
   if ((p = fork()) == 0) {
      // Child process: do your work here
      exit(0);
   }
   else {
      childPids[ii] = p;
   }
}

/* Wait for children to exit */
int stillWaiting;
do {
   stillWaiting = 0;
    for (int ii = 0; ii < numberOfChildren; ++ii) {
       if (childPids[ii] > 0) {
          if (waitpid(childPids[ii], NULL, WNOHANG) != 0) {
             /* Child is done */
             childPids[ii] = 0;
          }
          else {
             /* Still waiting on this child */
             stillWaiting = 1;
          }
       }
       /* Give up timeslice and prevent hard loop: this may not work on all flavors of Unix */
       sleep(0);
    }
} while (stillWaiting);

/* Cleanup */
free(childPids);

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