c - 在不保持父进程执行的情况下获取子进程的返回值

Question

我需要能够从子进程获取返回值，而不必为它保留父进程的执行。

注意子进程中可能会发生运行时错误。

这是我正在尝试制作的程序:

//In parent process:
do
{
    read memory usage from /proc/ID/status
    if(max_child_memory_usage > memory_limit)
    {
        kill(proc, SIGKILL);
        puts("Memory limit exceeded");
        return -5; // MLE
    }
    getrusage(RUSAGE_SELF,&r_usage);
    check time and memory consumption
    if(memory limit exceeded || time limit exceeded)
    {
        kill(proc, SIGKILL);
        return fail;
    }
    /*
    need to catch the returned value from the child somehow with
    this loop working.
    Notice the a runtime error could happen in the child process.
    */
while(child is alive);

Answer 1

waitpid 函数有一个名为 WNOHANG 的选项，如果给定的 child 尚未返回，它会立即返回:

pid_t rval;
int status;
do {
    ...

    rval = waitpid(proc, &status, WNOHANG);
} while (rval == 0);

if (rval == proc) {
    if (WIFEXITED(status)) {
        printf("%d exited normal with status %d\n", WEXITSTATUS(status));
    } else {
        printf("%d exited abnormally\n");
    }
}

参见 man page for waitpid有关检查各种异常退出条件的更多详细信息。