Gearman (Part 2): Create jobs, add workers, do work

Other posts in this series

• Gearman (Part 1): Setup Gearmand
• Gearman (Part 2): Create jobs, add workers, do work
• Gearman (Part 3): More jobs, other stuff, a better title (soon after Part 2)

Now that Gearmand is setup we need to get some workers going. Gearman is itself language agnostic; it doesn’t really care if your client/worker is in Python, PHP or Ruby, to name a few. There are several libraries available to help you get going.

PECL::Gearman

In order to get clients and workers setup using PHP you need to have libgearman installed; this came with Gearmand from my previous post in this series. For this example I’ll be using the Gearman PECL extension. I assume you already have PHP installed on your system.

By default, the configure script looks in /usr/local, /usr, and /opt/local to find the libgearman header files. If you’re using Homebrew, MacPorts, or installed from source you should have no problem.

To install using PECL, run

~$ (sudo) pecl install gearman-beta

The -beta is required since there is no full fledged stable release to use at this time.

Side Note: This should work fine for installations of libgearman I covered previously, but if you’re like myself and have your Homebrew installed elsewhere (I use Cinderella), your header files are in a different place, and you’ll need to compile the extension by downloading the source, extracting it, and running the following

1 ~$ cd Downloads/gearman-0.7.0/gearman-0.7.0
2 ~$ phpize
3 ~$ ./configure --with-gearman=`brew --prefix`
4 ~$ make
5 ~$ (sudo) make install
6 Installing shared extensions:     /usr/lib/php/extensions/no-debug-non-zts-20090626/
7 ~$

When the installation completes, you should receive instructions on activating the extension. They typically involve updating your php.ini file to include the extension_dir and add extension=gearman.so near the end of the file. After that, restart your sever.

To confirm everything is OK, create a simple php file that echo’s out the gearman version:

//gearman_version.php
<?php
echo "Gearman version: " . gearman_version() . PHP_EOL;
?>

And run the file

~$ php gearman_version.php
Gearman version: 0.15

Creating Jobs

• Jobs are created by Clients, who send them to the Gearman server via Tasks
• A Task is communication about a job, such as “run this job” or “what is the status of this job”
• A Job is something the worker does
• Workers continuously waiting on the job server to tell them when to start and with what arguments
• Clients submit jobs and ask for status about jobs (both of those things are considered tasks)
• Workers actually perform the jobs

Source here

We’ll start with a very simple “reverse string” job to get going. First we’ll create the client to submit the job. We do so by instantiating a new GearmanClient object, set the server where Gearmand is running, and calling do with the job name and the workload:

//  reverse_do.php
<?php
# Create our client object.
$client= new GearmanClient();

# Add default server (localhost).
$client->addServer('localhost','4730');

echo "Sending job...\n";
# Send reverse job

$result = $client->do("reverse", "Hello World!");

echo "Result: {$result}" . PHP_EOL;
?>

You can run this on the command line like so:

~$ php reverse_do.php 
Sending job...

The client will wait for the response (there are other types of jobs where the client does not wait, called background jobs).

Now we create a worker in a similar process: instantiating a new GearmanWorker object and set the server where Gearmand is running, except now we register a method of work that we can do, and define that function:

//  reverse_worker.php
<?php

$worker = new GearmanWorker();
$worker->addServer('localhost','4730');
$worker->addFunction('reverse', 'reverse_function');

while ($worker->work());

function reverse_function($job)
{
    //  For example purpose
    echo "Received job: {$job->handle()}" . PHP_EOL; 
    return strrev($job->workload());
}
?>

Now we run the worker from another terminal session. Because we’ve put the worker in an endless while loop, the worker will connect to the server and perform jobs until we kill the process with cntrl+c

~$ php reverse_worker.php 
Received job: H:Waffles.local:11

Back on the original terminal session, where we left the client waiting, you should see an update:

~$ php reverse_do.php 
Sending job...
Result: !dlroW olleH
~$ 

The Gearmand server held on to the job until a worker arrived that could preform the work. Once our worker fired up, the server handed the job over, the worker did the work, and told the server it was done and could accept more work. The server in turn passed the result back to the client, and the client process terminated, printing the reversed string.

@ctshryock

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