Blocking and non-blocking of the PHP multi-process parent process

The blocking process in PHP is primarily the parent process waiting for the child process to exit.

The 1.php code is as follows:

<?php//defines the number of processes define (' Fork_nums ', 5);//used to save the process Pid$pids = array ();//We create 5 sub-processes for ($i = 0; $i < fork_nums; + + $i) {    $pids [$i] = Pcntl_fork ();    if ($pids [$i] = = 1) {die        (' fork error '),    } else if ($pids [$i]) {        //This is the parent process space, i.e. the main process        //Our For loop first entered here , pcntl_wait suspends the current master process, waits for the first child process to complete exit        //Note For Loop code is in the main process, hangs the main process, the equivalent of the current for loop is also blocked here        //After the first child process exits, and then creates a second child process , hang up here, wait for the second child process to exit, continue to create a third, and so on.        pcntl_wait ($status);    } else {        //Here is the child process space        echo "Parent process ID:", posix_getppid (), "Process ID:", posix_getpid (), "{$i} \ r \ n";        We let the child process wait for 3 seconds before exiting        sleep (3);        Exit;    }}

The above code results are as follows:

What happens if we take pcntl_wait out of the for loop?

The 2.php code is as follows:

<?php//defines the number of processes define (' Fork_nums ', 5);//used to save the process Pid$pids = array ();//We create 5 sub-processes for ($i = 0; $i < fork_nums; + + $i) {    $pids [$i] = Pcntl_fork ();    if ($pids [$i] = = 1) {die        (' fork error '),    } else if ($pids [$i]) {    } else {        //Here is the child process space        echo "Parent process ID:", Posix_getppid (), "Process ID:", posix_getpid (), "{$i} \ r \ n";        We let the child process wait for 3 seconds before exiting        sleep (3);        Exit;    }} We put the pcntl_waitpid out of the for loop so that creating a child process in the for loop would not block//But it would still block, and the main process would wait until 5 of the child processes exited before exiting. foreach ($pids as $pid) {    pcntl_waitpid ($pid, $status);}

The above code results are as follows:

The second parameter of the pcntl_wait can be used to set the main process not to wait for the child process to exit and continue execution of subsequent code.

The 3.php code is as follows:

<?php//defines the number of processes define (' Fork_nums ', 5);//used to save the process Pid$pids = array ();//We create 5 sub-processes for ($i = 0; $i < fork_nums; + + $i) {    $pids [$i] = Pcntl_fork ();    if ($pids [$i] = = 1) {die        (' fork error ');    } else if ($pids [$i]) {        //This is the parent process space, which is the main process        // This is only a bit different from the 1.php code, that is, add the second parameter Wnohang        //for loop here, will not suspend the main process, but continue to execute subsequent code        pcntl_wait ($status, Wnohang);    } else {        //Here is the child process space        echo "Parent process ID:", posix_getppid (), "Process ID:", posix_getpid (), "{$i} \ r \ n";        We let the child process wait for 3 seconds before exiting        sleep (3);        Exit;    }} Here we wait 10 seconds, otherwise the child process has not finished, the main process is exited, see no effect sleep (10);

The above code results are as follows:

Code 3.php As with the 2.php effect, the pcntl_wait () function is used only to let the parent process wait for the child process to exit, which by default blocks the main process.

Blocking and non-blocking of the PHP multi-process parent process