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--- action:Semaphore_Lock [2019/08/25 00:43] – [Preventing Multiple Executions of One or More Macros] JMichaelTX
+++ action:Semaphore_Lock [2022/10/31 01:42] (current) – [Macros Triggered by the User] peternlewis
@@ Line 1: / Line 1: @@
 ====== Semaphore Actions ======
-The //Semaphore actions// (Lock, Unlock and Reset) allow you prevent (a) multiple triggers of the same macro from executing simultaneously, and/or (b) multiple macros from executing simultaneously.
+The //Semaphore actions// (Lock, Unlock and Reset) allow you to prevent (a) multiple triggers of the same macro from executing simultaneously, and/or (b) multiple macros from executing simultaneously.
 ===== Background =====
@@ Line 9: / Line 9: @@
 ==== Macros Triggered by the User ====
+Although it is rare to have multiple macros triggered at the same time, the normal behaviour in Keyboard Maestro is that all triggered macros run simultaneously, with actions from each independently triggered macro running at the same time.
-The normal case is that all triggered macros run simultaneously (or synchronously), although you rarely have multiple macros triggered at the same time.
+Most macros are triggered explicitly manually, and typically the user waits for them to complete before they trigger another macro. So macros triggered like this will rarely run at the same time.
-Most macros are triggered explicitly by the user, and the user expects them to complete before he/she triggers another macro. So macros triggered like this will rarely run at the same time.
 ==== Macros Triggered in the Background ====
@@ Line 22: / Line 21: @@
 Occasionally there are cases where multiple macros can be triggered, or the same macro triggered again, before the other macros complete. This can sometimes cause a problem, which needs to be prevented.
-**The primary purpose of using a //Semaphore Lock// is to prevent simultaneous macro executions of the same, or related, macros.**\\
+**The //Semaphore actions// require a _Semaphore Name_, which uniquely identify each _Semaphore Lock_.**  Use a different _Semaphore Name_ to identify different (independent) _Semaphore Locks_.
-In order to achieve this:
+**In order to prevent simultaneous executions (instances) of one or more macros that have _Semaphore Locks_ with the same _Semaphore Name_, do the following:**\\
   * Place a //Semaphore Lock// Action (using the same Semaphore Name) as the first action of each Macro that you wish to prevent executing simultaneously.
-  * The lock will remain in place preventing any other macros that try to execute until the first macro completes, or until you execute a Semaphore Unlock action.
+  * The lock will remain in place, preventing the other macros from executing, until the current macro instance (("macro instances" refers to both additional instances of the same macro _and_ instances of other macros that use the same named Semaphore Lock Action.)) completes or until the semaphore is unlocked with a Semaphore Unlock action.
-  * You can also cause all additional macro instances to be immediately cancelled by setting a very short timeout (1 hundredth of a second) for the Semaphore Action.
+  * When the Semaphore is _unlocked_ the next macro instance in the queue will execute in First In First Out (FIFO) order.  Since the first Action is a _Semaphore Lock_, only one macro instance is executed at a time.
+  * You can also cause all additional macro instances  to be immediately cancelled by setting a very short timeout (1 hundredth of a second) for the Semaphore Lock Action.  When the Semaphore Local Action times out, it cancels the pending execution of that macro instance.
-The //Semaphore actions// take a name, and different names can be used for different (independent) locks.
 Semaphore Lock can be balanced by a Semaphore Unlock, but a Semaphore is implicitly unlocked when the macro that locked it completes.