fork（） - 多个进程和系统调用

Question

I am writing a mapreduce program that uses multiple I/O pipes (one pipe per process) to get some final results. I am having a problem with creating the processes. Specifically, I am getting the following error:

wait error: Interrupted system call

This is my code that spawns processes:

while (values[inc]!=NULL) //provided array of text lines
{
    if ((pid = fork()) == -1) {
        perror("fork error");
        exit(EXIT_FAILURE);
    }    

    else if (pid == 0) {             /* start of child process      */
        printf("Child process...\n");
        /* pipes[inc][1] is a file descriptor to which myMap writes some data
           using the write() system call
           mr is a struct that holds other function pointers */
        mr->myMap(pipes[inc][1],values[inc]); 
        exit(0);
    }
    else {                           /* start of parent process     */
        printf("Parent process...\n");

        if ((wpid = wait(&status)) == -1)
        /* Wait for child process.      */  
            perror("wait error");
        else {                       /* Check status.                */
            if (WIFSIGNALED(status) != 0)
                printf("Child process ended because of signal %d\n",
                       WTERMSIG(status));
            else if (WIFEXITED(status) != 0)
                printf("Child process ended normally; status = %d\n",
                       WEXITSTATUS(status));
            else
                printf("Child process did not end normally\n");
        }
        //close(fd[1]);

        printf("Parent process ended\n");
    }
    inc++;
}

After this I am creating one thread

pthread_t newThread;
pthread_create(&newThread,NULL,threadFunction,values);
pthread_join(newThread,NULL);

The threadFunction uses select() function to find out which file descriptor is ready to be read and reads it and puts data in a dictionary.

When running form gdb debugger, the program output:

Parent process...
Child process...
wait error: Interrupted system call
Parent process ended
Parent process...
Child process ended normally; status = 0
Parent process ended
Parent process...
Child process...
Child process...
wait error: Interrupted system call
Parent process ended

I don't know how to resolve the issue. Any suggestions?

Thanks!

Answer 1

You need to put your wait() call into a loop and if it returns an error (-1) and errno == EINTR continue the loop. Any other error is a real error and should be treated as such.

Things like profiling timers can cause signals to be sent to the process, however the signal probably causing the interruption is SIGCHLD , which as you know is called when a child process changes state .

EDIT: OK, I'll write the answer in code:

do
{
    wpid = wait(&status);
}
while (wpid == -1 && errno == EINTR);
if (wpid == -1)
{
    perror("wait error");
    return -1;
}
else
{
    // we have wait status
    ...
}