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- Overview
- Simple management of events
- Principle
- Example: Application used to manage a spelling checker
- WLanguage functions
- Remark
- Advanced management of events
- Principle
- Implementation
- Functions for advanced management of events
Synchronizing threads via events
Events can be used to synchronize the different threads of an application. Therefore, a thread can wait for the execution of another thread. Two management modes can be used to manage events:
Simple management of events Principle Two threads are run in parallel (a main thread and a secondary thread for instance). One of the threads waits for a specific action from the second thread before it can be run. Example: Application used to manage a spelling checker When the user types the SPACE character in an edit control, the spelling checker is automatically started to check the previous word. In this case, the spell check is managed in a secondary thread. Whenever the SPACE key is pressed, the main thread sends a signal to the secondary thread in order to start the spelling checker. The code for this kind of application is as follows: - Code of the main thread:
IF Right(SAI_Saisie1, 1) = " " THEN
ThreadSendSignal("ThreadCorrection")
END
- Code of the secondary thread (ThreadSpellCheck):
LOOP
IF ThreadWaitSignal() = True THEN
LanceCorrection()
END
END
WLanguage functions The following functions are used to perform a simple management of events:
| | | ThreadSendSignal | The current thread sends a signal to the specified thread in order to unlock it. | | ThreadWaitSignal | Locks the current thread until it receives a signal from another thread. |
Remark Semaphores and events are system objects identified by their name. They are shared among all the applications that run on a computer. Therefore, two applications (or two instances of the same application) use the same objects if the same name is used. To create unique names, use Instance to implement the desired name. Advanced management of events Principle An advanced management of events consists in communicating between several threads (more than 2). Some threads are waiting for a task performed by the main thread. When the main thread performs this task, it sends a signal to all the secondary threads. Implementation Two methods can be used to implement an advanced management of events: - Using AutomaticEvent and ManualEvent.
- Using named events (recommended method to manage the options to share events).
Method 2: Using named signals (recommended method for managing signal sharing options)
The steps for implementing an advanced management of events are as follows: - Signal creation (function EventCreate). By default, this event is closed.
- Waiting an event (EventWait).
- Synchronizing threads:
- using the EventChange function: the signal is open. All waiting threads are unlocked and the event is automatically closed (default operating mode).
 via EventOpen and EventClose.
- Destroying the event (EventDestroy).
Functions for advanced management of events The following functions are used for an advanced management of events:
| | | EventChange | Modifies the status of an event. | | EventClose | Closes a synchronization event between several threads. | | EventCreate | Creates an event. | | EventDestroy | Explicitly destroys an event. | | EventOpen | Opens a synchronization event between several threads. | | EventWait | Locks the current thread while waiting for the specified event to be opened. |
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