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action:Semaphore_Lock [2017/03/05 21:45]
peternlewis [Forum]
action:Semaphore_Lock [2019/08/25 20:43]
JMichaelTX Rev #2
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-The //Semaphore actions// (Lock, Unlock and Reset) allow you to limit the execution of sequence ​of actions.+====== 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. 
 + 
 +===== Background =====
  
 When you trigger a macro, the Keyboard Maestro Engine takes a copy of it and starts executing it.  If you trigger another macro before the first one finishes, that will start executing as well - both will be executing more or less simultaneously. When you trigger a macro, the Keyboard Maestro Engine takes a copy of it and starts executing it.  If you trigger another macro before the first one finishes, that will start executing as well - both will be executing more or less simultaneously.
  
-The normal case is that macros just all run simultaneously, ​and you rarely have multiple macros ​running ​at the same time.+==== Macros Triggered by the User ==== 
 + 
 + 
 +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 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 ==== 
 + 
 +But there is another class of macros that operate in the background, most especially time triggered macros. Macros that are triggered independent of the UI and the user's awareness. Typically these will be written so as not to impact the user since the user won't be expecting them to run. So they might be things like backup scripts, or automatic download scripts, or the like. Things that happen in the background, or that wait for the user to be idle before doing stuff in the foreground. Often these sorts of macros run for a significant amount of time. 
 + 
 +===== Preventing Multiple Executions of One or More Macros ===== 
 + 
 +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.
  
-Most macros are executed explicitly by the userand the user expects them to do their thing and then the user goes on to the next thing, so macros like this will rarely run at the same time since the user is highly aware of what is going on+**The //Semaphore actions// require a _Semaphore Name_which uniquely identify each _Semaphore Lock_.** ​ Use a different _Semaphore Name_ to identify different (independent) _Semaphore Locks_.
  
-But there is another class of macros that operate in the backgroundmost especially time triggered macros. Macros that are triggered independent of the UI and the user's awareness. Typically these will be written so as not to impact the user since the user wont be expecting them to run. So they might be things like backup scripts, or automatic download scripts, or the like. Things that happen in the background, or that wait for the user to be idle before doing stuff in the foreground. Often these sorts of macros run for a significant amount of time.+**In order to prevent simultaneous executions (instances) ​of one or more macros that have _Semaphore Locks_ with the same _Semaphore Name_do the following:​**\\
  
-Occasionally there are cases where multiple macros are running ​simultaneously (or the same macro is running multiple timesand care needs to be taken that the sequences ​of actions are not intermixed.+  * 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 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. 
 +  * When the Semaphore is _unlocked_ the next macro instance in the queue will execute in First In First Out (FIFOorder. ​ 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.
  
-This is a primary purpose of using a //Semaphore Lock// - just place one at the start of the sequence. ​ The lock will remain in place (and any other macros that try to execute that action will have to wait) until the end of the macro, or until you execute a Semaphore Unlock action. 
  
-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. Semaphore Lock can be balanced by a Semaphore Unlock, but a Semaphore is implicitly unlocked when the macro that locked it completes.
action/Semaphore_Lock.txt · Last modified: 2019/08/25 20:43 by JMichaelTX