Running a background process with shell_exec from the PHP built-in webserver

Question

The PHP built-in webserver does not seem to handle shell_exec()ing background processes properly; the request hangs until the background process is complete, even if it's explicitly placed in the background with &.

Example:

$ ls
runit.php
$ cat runit.php 
<?php
echo "Here we are\n";
shell_exec("sleep 5 &");
echo "and the command is done\n";
?>
$ php -S localhost:7891
PHP 5.5.9-1ubuntu4.9 Development Server started at Mon May 18 19:20:12 2015
Listening on http://localhost:7891
Press Ctrl-C to quit.

and then in another shell:

$ GET http://localhost:7891/runit.php
(...waits five seconds...)
Here we are
and the command is done

This shouldn't happen, and indeed doesn't if one uses a production-grade webserver. Is there any way to work around it?

(Note: this is not a flushing problem. Adding flush() after the first echo doesn't make it happen, and the request still hangs until the background process is complete.)

score 1 · Accepted Answer · answered May 18 '15 at 19:40

This is acknowledged as a bug by PHP, but won't be fixed in the built-in webserver. However, the bug report does also suggest a workaround; set a correct Content-Length on the response, and then the receiving browser will close the request at the client end after receiving that much data, thus working around the problem.

score -1 · Answer 2 · answered May 18 '15 at 18:27

your options are:

1) Use separate thread to run your processes

<?php 
for ($i = 1; $i <= 5; ++$i) { 
        $pid = pcntl_fork(); 

        if (!$pid) { 
            sleep(1); 
            print "In child $i\n"; 
            exit($i); 
        } 
    } 

    while (pcntl_waitpid(0, $status) != -1) { 
        $status = pcntl_wexitstatus($status); 
        echo "Child $status completed\n"; 
    } 
?>

2) you can append '> /dev/null 2>/dev/null &' at the end of your shell exec, which will get rid of all output too, but it will run the command. making it look like

shell_exec('sleep 5 > /dev/null 2>/dev/null &');

Sadly, neither approach works. What I want is the PHP request to return immediately, and the background process to carry on running after the PHP request has returned. Redirecting stdout and stderr to /dev/null doesn't change anything (the request still takes 5 seconds to complete), and fork()ing doesn't either, I'm afraid. They may work in a "proper" web server, but not in the PHP built-in server. — sil, May 18 '15 at 18:46

Running a background process with shell_exec from the PHP built-in webserver

2 Answers2