(PECL gearman >= 0.5.0)
GearmanClient::setCreatedCallback — Set a callback for when a task is queued
$callback): boolSets a function to be called when a task is received and queued by the Gearman job server. The callback should accept a single argument, a GearmanTask object.
callbackA function to call
成功した場合に true を、失敗した場合に false を返します。