If you suddenly start getting a:

PHP Fatal error:  Uncaught exception 'GearmanException' with message 'Failed to set exception option' in

...on your GearmanWorker::work() calls, I was able to fix this by specifying values to GearmanWorker::addServer(), even if they are the same as the documented default values.

Crashes:

<?php
$gmw = new GearmanWorker();
$gmw->addServer();
$gmw->work();
?>

Works:

<?php
$gmw = new GearmanWorker();
$gmw->addServer("127.0.0.1", 4730);
$gmw->work();
?>

Go figure. :)

To properly test the server added you could use the following code:

<?php
// create the worker
$worker= new GearmanWorker();

// add the  job server (bad host/port)
$worker->addServer('127.0.0.2', 4731);

// define a variable to hold application data
$count = 0;

// add the reverse function
$worker->addFunction('reverse', 'my_reverse_function', $count);

// test job server response
if (!@$worker->echo('test data')) {
    die($worker->error());
}

// start the worker listening for job submissions
while ($worker->work());

function my_reverse_function($job, &$count)
{
    $count++;

    return $count . ': ' . strrev($job->workload()) . "\n";
}
?>

I was receving following message on add server Uncaught exception 'GearmanException' with message 'Failed to set exception option' in <<filename>>:<<linenumber >>
 was on centos 6.5

fixed by following steps:
yum install gearmand
/etc/init.d/gearmand start

PHP Fatal error:  Uncaught exception 'GearmanException' with message 'Failed to set exception option'

also indicates the gearmand daemon is not running.

The manual states that you get a TRUE on success and FALSE on failure. When I have attempted to connect to a server that is powered off I still get TRUE. The return from returnCode() is 0 which is the same as the returnCode() from a successful connection.

I have not yet found a way around this.

On Ubuntu (php7 php-gearman/xenial,now 2.0.2+1.1.2-1+deb.sury.org~xenial+1 amd64) this function throws a GearmanException. 
Please use in try catch

No socket I/O happens in addserver.