fork() - multiple processes and system calls

c, fork

Solution

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
    ...
}

Problem

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!

Original source