Handling SIGCHLD, how to record the return values of children as they die

Question

void childSignalHandler(int signo) {
    int status;

    pid_t pid = wait(&status);

    struct PIDList* record = getRecordForPID(childlist, pid);
    if (recor         


        

Answer 1

This should do the job, if you set your function as a handler for SIGCHLD.

However, SIGCHLD can be send to parent process not only after the child exited. Some other events are signaled this way as well (for instance when the child is stopped). See man wait(3) for detailed explanation.

Answer 2

Note signals are not queued. If two children die in quick succession, you may only recieve one SIGCHLD. So, you should actually loop around calling waitpid() until there are no more exiting processes to handle:

int status;
pid_t pid;

while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
    if (WIFEXITED(status)) {
        struct PIDList *record = getRecordForPID(childlist, pid);

        if (record != NULL)
            record->returnValue = WEXITSTATUS(status);
    }
}