Description:
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addTask and the other five functions like it don't do any sort of type checking or conversion.

https://github.com/hjr3/pecl-gearman/blob/master/php_gearman.c#L2327

Using Z_STRVAL_P on a non-string can have unexpected results including segfaults. These functions should all probably be checking if Z_TYPE_P(zworkload) != IS_STRING) and throw a warning/return false or do implicit type conversion to strings.

Test script:
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<?php

$gearman = new \GearmanClient();
$gearman->addServers('127.0.0.1:4730');
$gearman->addTask('crash', array('data' => 'overflow'));
$gearman->runTasks();

Expected result:
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Warning: addTask() expects parameter 2 to be string, array given in X on line X

Actual result:
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Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 18446744073365895129 bytes) in /tmp/gearman.php on line 6