SynchronousUpdating

is an option for Manipulate, Dynamic, and related functions that specifies whether or not to evaluate their contents synchronously.

Details

If a dynamic object that needs to be updated has the setting SynchronousUpdating->True, the front end will wait for the necessary evaluation to be completed before going on to any other tasks.
If a dynamic object has the setting SynchronousUpdating->False, the front end will queue up its evaluation, and allow it to be performed asynchronously.
For dynamic objects that take a long time to update, the updating may time out unless the objects have SynchronousUpdating->False.
For dynamic objects with SynchronousUpdating->True the front end blocks until their evaluation is complete.
SynchronousUpdating->Automatic specifies that synchronous updating should be used when controls in an object such as Manipulate are active, and asynchronous updating should be used otherwise.

By default, Manipulate will time out if the contents take more than six seconds to evaluate:

If SynchronousUpdating is disabled, the evaluation will not time out:

Top