4.5. Fork Class

Fork class is a simple wrapper around C library function fork(). Main advantage of using Fork over fork() is that child termination process is handled internally by the static destructor of Fork.


class Fork {
    enum state_t { KILL_ON_EXIT, WAIT_ON_EXIT, LEAVE_ALONE };

    Fork (state_t s_ = WAIT_ON_EXIT);
    ~Fork ();

    bool isParent() const;
    bool isChild() const;

    pid_t getChildPID() const;

4.5.2. USAGE

Forking is done by instantiation Fork object. For example:

initServer ()
    // peform some initialization

    Fork ss (Fork::KILL_ON_EXIT);   // Fork and exec server-side.

    if (ss.isChild ()) {
        execlp ("bufio_tests", "bufio_tests",
                "-p", getPortName().c_str(),
                "-D", "~/log/bufioSdb",

        /*--- unreachable ---*/
        cerr << "error: " << "bufio_tests" << ": ";
	    cerr << "exec(3) failed: " << strerror (errno));
    else if (ss.isParent ()) {
        m_child_pid = ss.getChildPID ();
        cout << "Child PID " << m_child_pid << endl;
        sleep (2);      // Give the server chance to run

Each Fork object has a state. By default, the state assigned is Fork::WAIT_ON_EXIT. Here are all possible states that Fork object can take:

Fork doesn't provide the exit status of the child process. If you need to examine the exit status, you have to explicitly wait for the status with ::wait(2).

When Fork is used in GenServer application, GenServer sets up SIGCHLD's disposition to SIG_IGN with the following side effect:

" If process sets SIGCHLD's disposition to SIG_IGN, child processes will not create zombie processes when they terminate (see exit(2)). If the parent process subsequently waits for its children to exit, it blocks until they are all terminated; it then returns -1 with errno set to ECHILD (see wait(2) and waitid(2)). "

For further example, please see $src/tests/fork_test.cpp. Fork class is used extensively by other test programs as well.