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- Characteristics of a thread created in WLanguage
- Thread and HFSQL
- Characteristics of WLanguage procedure
- Lifespan of the thread
- Managing errors
- Forbidden processes
- Stopping a thread
ThreadExecute (Function) In french: ThreadExecute Starts the execution of a secondary thread. The statement is a non-locking statement: the two processes are run in parallel.
ThreadExecute("Thread1", threadNormal, ThreadProcedure)
...
// Call to a global method of a class
ThreadExecute("Thread2", threadNormal, CClass::GlobalMethod)
// Run a thread while passing parameters
sDate is string
sDate = DateSys()
// Run the thread
ThreadExecute("THREADNAME", threadNormal, "pExecQry", sDate)
// Details of the "pExecQry" procedure
// This procedure expects a date in parameter of a query
PROCÉDURE pExecQry(sDate)
IF HExecuteQuery(Del_Date, hQueryDefault, sDate) = False THEN
Error(HErrorInfo())
ELSE
HReadFirst(Del_Date)
END
Syntax
ThreadExecute(<Thread name> , <Options> , <WLanguage procedure> [, <Parameter 1> [... [, <Parameter N>]]])
Remarks Characteristics of a thread created in WLanguage A thread created in WLanguage can only be a procedure or a class method. The thread cannot correspond to a WLanguage process (code of a control for example). If the thread is a class method, ThreadExecute must be run from one of the processes of the class (constructor or method). Thread and HFSQL When running ThreadExecute, the HFSQL contexts are automatically duplicated: the number of HFSQL contexts is equal to the number of threads currently run. The entire HFSQL context is copied (filter, search condition, ...). The HFSQL context evolves independently in each thread. This allows you to perform two different browse operations on the same file in two different threads. Two methods can be used to copy the HFSQL contexts: - Full copy of context (by default)
 Versions 20 and laterLight copy of context.  New in version 20Light copy of context.
Example: A filter is created on the Customer file. ThreadExecute is called to create the CTX2 thread. The Customer file is filtered in each thread. The filter will still be enabled in the CTX2 thread even if the filter is disabled in the main thread. Caution: If several threads are used on the data files, we advise you to customize the management of HFSQL errors to avoid displaying the default windows. To do so, use HOnError to disable the automatic management of errors or to redirect the management of errors to a custom procedure (without displaying windows). See Assisted management of HFSQL errors for more details. Note: From version 19, HFSQL is the new name of HyperFileSQL. Characteristics of WLanguage procedure Caution: The calls to Info, Error, ... lock all the threads currently run. Note: The parameters passed to the procedure are passed by value (and not by address). The thread is automatically stopped at the end of the execution of the WLanguage procedure run by ThreadExecute. The thread is also stopped in the following cases: - if ThreadExecute is called from the code of a window, the thread will be stopped when closing the window.
- if ThreadExecute is called from a global process (initialization, explicit call in the main context), the thread will be stopped at the end of the application.
- if ThreadExecute is called in a class method, the thread is stopped when destroying the object.
To force the execution of the thread in the main context, use the threadGlobalContext constant. To force the thread to stop, use ThreadStop. This function can be used to stop a thread from the main thread. Note: Make sure that the threads are stopped (by ThreadState or ThreadWait) before closing the windows or destroying the objects. A fatal error occurs in the following cases: - if the procedure does not exist.
- if a thread with the same name is currently run.
Forbidden processes Caution: The following processes cannot be run in the threads: | Caution: it is not allowed to handle the interface (windows, controls, ...) in a secondary thread.
When a secondary thread must interact with the user or update the interface, it must use a process started from the main thread. This process can correspond to:- a global procedure of the project or a local procedure (of a window, ...) called by ExecuteMainThread,
- the "Request for refreshing the display" process of a window run by RequestRefreshUI.
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https://windevdesenvolvimento.blogspot.com/2019/01/dicas-1996-windev-threads-02.html |
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