Synchronizing threads via signals

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Overview
Simple management of signals
Principle
Example: Application managing a spelling checker
WLanguage functions
Note
Advanced management of signals
Principle
Implementation
The functions for advanced management of signals

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Synchronizing threads via signals

Overview

The 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 signals:

simple management: synchronization between two threads.
advanced management: synchronization between several threads (more than two).

Versions 17 and later

This feature is now available for the Windows Phone applications.

New in version 17

This feature is now available for the Windows Phone applications.

Versions 19 and later

This feature is now available for WINDEV applications in Linux.

This feature is now available for the WEBDEV sites in Linux.

New in version 19

This feature is now available for WINDEV applications in Linux.

This feature is now available for the WEBDEV sites in Linux.

This feature is now available for WINDEV applications in Linux.

This feature is now available for the WEBDEV sites in Linux.

Versions 21 and later

This feature is now available for the applications in Universal Windows 10 App mode.

New in version 21

This feature is now available for the applications in Universal Windows 10 App mode.

Simple management of signals

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 managing 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(EDT_Edit1, 1) = " " THEN
ThreadSendSignal("ThreadCorrection")
END

Code of secondary thread (ThreadCorrection):

LOOP
IF ThreadWaitSignal() = True THEN
StartCorrection()
END
END

WLanguage functions

The following functions are used to perform a simple management of signals:


Versions 09 and later ThreadSendSignal New in version 09 ThreadSendSignal ThreadSendSignal	The current thread sends an event to the specified thread in order to unlock it.
Versions 09 and later ThreadWaitSignal New in version 09 ThreadWaitSignal ThreadWaitSignal	Locks the current thread until it receives an event from another thread.

Note

The semaphores and the signals 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 requested name.

In Java, the semaphores, the critical sections and the signals are unique for the application that created them. They cannot be shared between several applications.

Advanced management of signals

Principle

An advanced management of signals 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 signals:

Versions 20 and later
Using AutomaticEvent and ManualEvent.
New in version 20
Using AutomaticEvent and ManualEvent.
Using AutomaticEvent and ManualEvent.
Using named signals (recommended method to manage the options for signal share).

Versions 20 and later

Method 1: Using EventAutomatic and EventManual.
The steps for implementing an advanced management of signals are as follows:

Creating an AutomaticEvent variable or a ManualEvent variable. By default, this signal is closed. The signal is automatically destroyed when going outside the range of the corresponding variable.
Waiting for the signal (EventWait).
Synchronizing the threads with EventOpen and EventClose.

New in version 20

Method 1: Using EventAutomatic and EventManual.
The steps for implementing an advanced management of signals are as follows:

Creating an AutomaticEvent variable or a ManualEvent variable. By default, this signal is closed. The signal is automatically destroyed when going outside the range of the corresponding variable.
Waiting for the signal (EventWait).
Synchronizing the threads with EventOpen and EventClose.

Method 1: Using EventAutomatic and EventManual.
The steps for implementing an advanced management of signals are as follows:

Creating an AutomaticEvent variable or a ManualEvent variable. By default, this signal is closed. The signal is automatically destroyed when going outside the range of the corresponding variable.
Waiting for the signal (EventWait).
Synchronizing the threads with EventOpen and EventClose.

Method 2: Using named signals (recommended method to manage the options for signal share)
The steps for implementing an advanced management of signals are as follows:

Creating a signal (EventCreate). By default, this signal is closed.
Waiting for the signal (EventWait).
Synchronizing threads:
- by EventChange: the signal is opened. All the pending threads are unlocked and the signal is automatically closed (default operating mode).
- Versions 20 and later
  via EventOpen and EventClose.
  New in version 20
  via EventOpen and EventClose.
  via EventOpen and EventClose.
Destroying the signal (EventDestroy).

The functions for advanced management of signals

The following functions are used to perform an advanced management of signals:


Versions 09 and later EventChange New in version 09 EventChange EventChange	Modifies the status of an event.
Versions 20 and later EventClose New in version 20 EventClose EventClose	Closes a synchronization event between several threads.
Versions 09 and later EventCreate New in version 09 EventCreate EventCreate	Creates an event.
Versions 09 and later EventDestroy New in version 09 EventDestroy EventDestroy	Explicitly destroys an event.
Versions 20 and later EventOpen New in version 20 EventOpen EventOpen	Opens a synchronization event between several threads.
Versions 09 and later EventWait New in version 09 EventWait EventWait	Locks the current thread while waiting for the specified event to be opened.