Class Delay

Inheritance:

Object  »
  Delay

Delay implements a facility to pause a process for some amount of time. The simplest usage is like this:

(Delay forSeconds: 5) wait.

An instance of Delay responds to the message wait by suspending the caller's process for a certain amount of time. The duration of the pause is specified when the Delay is created with the message forMilliseconds: or forSeconds:. A Delay can be used again when the current wait has finished. For example, a clock process might repeatedly wait on a one-second Delay.

The maximum delay is (SmallInteger maxVal // 2) milliseconds, or about six days. A delay in progress when an image snapshot is saved is resumed when the snapshot is re-started. Delays work across millisecond clock roll-overs.

Class Variables:

The following class variables are used to manage all currently active delays:

• AccessProtect - Semaphore
  This semaphore ensures exclusive access to the class variables.

• ActiveDelay - Delay
  A reference to the active delay if there is one, otherwise nil. In a collection of several delays, the active delay is the one that expires first.

• ActiveDelayStartTime - Integer
  The time in milliseconds when the active delay expires.

• SuspendedDelays - SortedCollection
  A collection of all delays that wait expiration. The active delay is not an element of this collections. The suspended delays are sorted according to their expiration times; a delay that follows SuspendedDelays first cannot expire earlier then the delay at SuspendedDelays first.

• TimingSemaphore - Semaphore
  This semaphore is signalled from a primitive when the millisecond clock reaches a previously registered value. Class method primSignal:atMilliseconds: is used to express interest in a signal at a given future time.

Instance Variables:

• delayDuration - SmallInteger
  The duration of the delay in milliseconds

• resumptionTime - SmallInteger
  The system time in milliseconds at which the suspended process will resume. The value is only relevant if a process is currently waiting on delaySemaphore

• delaySemaphore - Semaphore
  This semaphore is used to queue a process that is waiting for expiration of the delay time.

• beWaitedOn - Boolean
  true if the process is currently registered in the queue of delaySemaphore, otherwise false.

Note that it is not allowed to specify a delay with a negative amount of time. An error notification is shown when you try to create a Delay with a negative amount of time. When you have to delay a process for a computed amount of time, you should always write something like this:

Delay forMilliseconds: (computedValue max: 0).