php script - Redirect input to another instance

Question

I have a php script who use flock() to deny multiple instance if script already running.

I would like the arguments provided in the script call are transferred to the existing process who would be able to handle them.

ie :

test.php :

#!/usr/bin/env php
<?php

$lock_file = fopen ( getcwd () . '/'. basename(__FILE__, '.php') . '.pid', 'c' );
$got_lock = flock ( $lock_file, LOCK_EX | LOCK_NB, $wouldblock );
if ($lock_file === false || (! $got_lock && ! $wouldblock)) :
    throw new Exception ( "Error opening or locking lock file" );
    error_log("execption thrown");
elseif (! $got_lock && $wouldblock) :
    exit ( "Another instance is already running; terminating.\n" );
endif;

while (true) :
    $input = $argv; // or incomming datas from other script ?
    unset($argv);
    if (is_array($input)) :
        foreach ($input as $a) :
            echo $a;
        endforeach;
    else :
        echo $input;
    endif;
endwhile;

?>

Now, if i run :

php -f test.php arg1 arg2

php -f test.php arg3 arg4

The second call exiting as well, but i would like the arg3 and arg4 are piped to the main process.

How can i do that ?

hanshenrik · Accepted Answer · 2016-10-08T20:35:02.247

in other words, you want a way to communicate with the process that already exists? aka IPC, there are a lot of ways to do this. the absolute fastest way being shared memory. but using a database, or unix sockets, would be easier to implement. here's an example using SQLite:

whenever convenient to process messages, do this:

while(NULL!==($message=check_for_message())){//handle all messages
echo "got a mesage!:";
var_dump($message);
}

and the "check_for_message" function:

//returns string("message") if there is a message available.
// else returns NULL
//Warning, do not try to optimize this function with prepared statements, unless you know what you're doing, in SQLIte they will lock the database from writing.
function check_for_message(){
static $db=false;
if($db===false){
$db=new PDO('sqlite:ipc.db3','','',array(PDO::ATTR_EMULATE_PREPARES => false,PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION));
$db->exec(
'
CREATE TABLE IF NOT EXISTS messages (id INTEGER PRIMARY KEY AUTOINCREMENT, message TEXT);

'
);
register_shutdown_function(function()use(&$db){
$db=NULL;
unset($db);
unlink("ipc.db3");
});
}
$message=$db->query("SELECT id,message FROM messages LIMIT 1",PDO::FETCH_ASSOC);

foreach($message as $ret){
$db->query("DELETE FROM messages WHERE id = ".$db->quote($ret['id']));
return $ret['message'];
}
return NULL;
}

and to send a message:

example usage:

foreach($argv as $arg){
sendmessage($arg);
}

function:

function sendmessage(string $message){
$db=new PDO('sqlite:ipc.db3','','',array(
PDO::ATTR_EMULATE_PREPARES => false,
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
));
$db->query('INSERT INTO messages (message) VALUES('.$db->quote($message).');');
}

notes: i think you could optimize that function by using WAL-mode sqlite and prepared statements. i think you could optimize it even more by putting it in shared memory by using PDO::ATTR_PERSISTENT , but afaik, that's hackish using undocumented features and i wouldn't expect it to work for things like HHVM PHP. on unixes (*BSD, Mac OS X, Linux, etc), using a unix socket would be faster anyway. it'd be even faster to use raw shared memory, but implementing message queues in shared memory is somewhat tricky.. you could also look into installing a signal handler, for instance, SIGUSR1 to indicate that there's a message waiting, see http://php.net/manual/en/function.pcntl-signal.php

I'll look IPC first, i didn't know this, otherwise, the sql approach seems a good solution however if it does not cause too many problems of simultaneous access. thanks! — Khorwin, Oct 08 '16 at 19:30
@Khorwin that's why i used SQLite over say, a plain text file or something. the SQLite engine takes care of synchronizing between an practically infinite number of processes that want to write to / read from it / delete from it, at the same time :) no race conditions, no accidental overwrites, all locking required is taken care of by SQLite. — hanshenrik, Oct 08 '16 at 20:03

php script - Redirect input to another instance

1 Answers1