Multiple threads in C program

问题:

I'm writing a Unix application in C which uses multiple threads of control. I'm having a problem with the main function terminating before the thread it has spawned have a change to finish their work. How do I prevent this from happening. I suspect I need to use the pthread_join primitive, but I'm not sure how. Thanks!

回答1:

Yes, you could use pthread_join() (see other anwers for how to do that). But let me explain the pthread model and show you another option.

In Unix, a process exits when the primary thread returns from main, when any thread calls exit() or when the last thread calls pthread_exit(). Based on the last option, you can simply have your main thread call pthread_exit() and the process will stay alive as long as at least one more thread is running.

回答2:

Yes one of doing this is to use pthread_join function: that's assuming your thread is in "joinable" state.

• pthread_create: after this function returns control, your thread will be executing your thread function.

• after pthread_create, use the tid from pthread_create to pthread__join.

If your thread is detached, you must use some other technique e.g. shared variable, waiting on signal(s), shared queue etc.

Great reference material available here.

回答3:

There are a number of different ways you can do this, but the simplest is to call pthread_exit() before returning from main().

Note that this technique works even if the thread you want to wait for is not joinable.

回答4:

You may want to look at this page: http://publib.boulder.ibm.com/iseries/v5r2/ic2924/index.htm?info/apis/users_25.htm

 rc = pthread_create(&thread, NULL, threadfunc, NULL);   checkResults("pthread_create()\n", rc);    printf("Wait for the thread to exit\n");   rc = pthread_join(thread, &status); 

回答5:

Check this simple C code I wrote for one of my libraries

/*  *   Copyright (c) 2011 Dino Ciuffetti , TuxWeb S.r.l., NuvolaBase Ltd  *     *   This file is part of liborient.  *  *   Liborient is free software: you can redistribute it and/or modify  *   it under the terms of the GNU Lesser General Public License as published by  *   the Free Software Foundation, either version 3 of the License, or  *   (at your option) any later version.  *  *   Liborient is distributed in the hope that it will be useful,  *   but WITHOUT ANY WARRANTY; without even the implied warranty of  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the  *   GNU Lesser General Public License for more details.  *  *   You should have received a copy of the GNU Lesser General Public License  *   along with Liborient.  If not, see . */  #include  #include  #include  #include   //pthread_rwlock_t ptr_thr_lock = PTHREAD_RWLOCK_INITIALIZER;  typedef struct {         int t; } thread_arguments;  void *thread_stuff(void *args) {         thread_arguments *t_args;         int tid;          t_args = (thread_arguments *)args;         //pthread_rwlock_rdlock(&ptr_thr_lock);         tid = t_args->t;         //pthread_rwlock_unlock(&ptr_thr_lock);          /*while (1) {         sleep (1);*/         printf("Thread #%i!\n", tid);         /*}*/          t_args = NULL;         pthread_exit(NULL);         return NULL; }  int wait_threads(pthread_t threads[], thread_arguments *t_args[], int nthreads) {         int t;         int rc;          // Waiting for threads termination         for(t=0; tt = t;                 //pthread_rwlock_unlock(&ptr_thr_lock);                  printf("Spawning thread: %i\n", t);                 rc = pthread_create(&threads[t], NULL, (void *)thread_stuff, (void *)t_args[t]);                 if (rc != 0) {                         printf("Error spawning thread %i: %i\n", t, rc);                         wait_threads(threads, t_args, rc+1);                         return t+1;                         break;                 }         }          return 0; }  int main() {         pthread_t threads[20];         thread_arguments *t_args[20];         int rc;          rc = spawn_threads(threads, t_args, 20);         if (rc > 0) {                 printf("Failed spawning thread number %i\n", rc-1);                 return 1;         }          rc = wait_threads(threads, t_args, 20);          return 0; } 

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