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--- at:tutorial:appendix [2008/07/10 16:46] – * tvcutsem
+++ at:tutorial:appendix [2008/07/10 17:21] – added tvcutsem
@@ Line 576: / Line 576: @@
 ==== Timing Utilities ====
+The module ''/.at.support.timer'' provides utility functions to schedule code for execution at a later point in time. Its most useful control construct is the following:
+<code>
+def subscription := when: timeoutPeriod elapsed: {
+  ...
+}
+</code>
+The ''when:elapsed:'' function takes as its arguments a timeout period (in milliseconds) and a block closure and schedules the closure for execution after the given timeout period. The function returns a subscription object whose single ''cancel'' method can be used to abort the execution of the scheduled code. Once ''cancel'' has been invoked, it is guaranteed that the closure will no longer be executed by the timer module.
+The milliseconds used to define the timeout period must be provided as a Java ''long'' value. To construct such a value from an AmbientTalk number, the timer module defines the following auxiliary functions:
+  * ''millisec(ms)'' => convert AmbientTalk number to a Java long value representing a timeout period in milliseconds.
+  * ''seconds(s)'' => convert AmbientTalk number to a Java long value representing a timeout period in seconds.
+  * ''minutes(m)'' => convert AmbientTalk number to a Java long value representing a timeout period in minutes.
+Additionally, the timer module defines a function ''now()'' which returns the current system time as a Java long value.
+The timer module also defines a function ''whenever:elapsed:'' which repetitively invokes the given block closure every time the timeout period has elapsed. The returned subscription object can be used to eventually stop the repetitive invocation of the closure.
+The timer module defines a small number of additional utility functions which can be found in the file ''at/support/timer.at''.
 ==== Logging Framework ====