Is there a version of the wait() system call that sets a timeout?

Question

Is there any way to use the wait() system call with a timeout, besides using a busy-waiting or busy-sleeping loop?

I've got a parent process that forks itself and execs a child executable. It then waits for the child to finish, grabs its output by whatever means appropriate, and and performs further processing. If the process does not finish within a certain period of time, it assumes that its execution timed out, and does something else. Unfortunately, this timeout detection is necessary given the nature of the problem.

Answer 1

There's not a wait call that takes a timeout.

What you can do instead is install a signal handler that sets a flag for SIGCHLD, and use select() to implement a timeout. select() will be interrupted by a signal.

static volatile int punt;
static void sig_handler(int sig)
{
    punt = 1;
}

...

struct timeval timeout = {10,0};
int rc;

signal(SIGCHLD, sig_handler);

fork/exec stuff
//select will get interrupted by a signal

rc = select(0, NULL,NULL,NULL, &timeout ); 
if (rc == 0) {
// timed out
} else if (punt) {
    //child terminated
}

More logic is needed if you have other signal you need to handle as well though

Answer 2

You can use waitpid together with the WNOHANG option and a sleep.

while(waitpid(pid, &status, WNOHANG) == 0) {
    sleep(1);
}

But this will be an active sleeping. However I see no other way using the wait type of functions.