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  • Characteristics of a thread created in WLanguage
  • Thread and HFSQL
  • Characteristics of WLanguage procedure
  • Life cycle of a thread
  • Managing errors
  • Forbidden processes
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Stored procedures
Starts the execution of a secondary thread. The statement is a non-locking statement: the two processes are run in parallel.
Reminder: A thread is a process run in parallel with the current application (main thread). It allows you to run a task in the background, for example (backup, etc.).
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
PROCEDURE pExecQry(sDate)
IF HExecuteQuery(Del_Date, hQueryDefault, sDate) = False THEN

Executing a thread by naming it (Compatible syntax) Hide the details

ThreadExecute(<Thread name> , <Options> , <WLanguage procedure> [, <Parameter 1> [... [, <Parameter N>]]])
<Thread name>: Character string (with quotes)
Name that will be given to the thread. This name will be used by all thread management functions. It cannot correspond to an empty string ("")
<Options>: Constant
Mode for starting the thread.
Versions 18 and later
New in version 18
Waits for the actual start of the thread before continuing the execution.
Versions 16 and later
New in version 16
Forces the use of the global context of the project if the thread is run from a window. The thread will continue to run until the application is closed.
The window context is used by default, therefore the thread is stopped when closing the window.
Remark: If ThreadExecute is used in a global initialization code (project, class or set) or from any procedure or method called from a global initialization code, this constant has no effect.
threadNormalStarts the thread in normal mode. The HFSQL context is copied during the first use of a HFSQL feature.
(Default value)
Triggers the immediate copy of current HFSQL context.
Recommended if the thread must take into account the current positions in the files and queries of caller context.
Versions 20 and later
New in version 20
Triggers the immediate copy of part of current HFSQL context.
Only the directories containing the data files in HFSQL Classic mode and/or the connections in HFSQL Client/Server mode are stored.
<WLanguage procedure>: Procedure name
Name of the WLanguage procedure run. This procedure is run in parallel with the application.
<Parameter 1>: Optional
Parameters that will be passed to the procedure. Caution: these parameters are passed by value (not by reference).
<Parameter N>: Optional
Parameters that will be passed to the procedure. Caution: these parameters are passed by value (not by reference).

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, etc.). The HFSQL context evolves independently in each thread.
This allows you, for example, to perform two different browse operations on the same data file in two different threads.
Two methods can be used to copy HFSQL contexts:
  • Full copy of context (by default)
  • Versions 20 and later
    Light copy of context.
    New in version 20
    Light copy of context.
    Light copy of context.
For more details on how HFSQL contexts are copied and their limits (depending on the database used), see Managing HFSQL contexts.
  • A filter is created on the Customer data file.
  • ThreadExecute is used to create the thread named CTX2.
  • The Customer data file is filtered in each thread (main and CTX2). The filter will still be enabled in the CTX2 thread even if the filter is disabled in the main thread.
Special cases:
  • Assisted management of HFSQL errors: 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.
  • Write operations and assignments in a thread: If write operations or assignments are performed in a thread, the other threads currently run do not share this information. Some inconsistencies may occur.
Remark: 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.
Remark: The parameters passed to the procedure are passed by value and not by reference.

Life cycle of a thread

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.
Remark: Make sure that the threads are stopped (by ThreadState or ThreadWait) before closing the windows or destroying the objects.

Managing errors

A fatal error occurs in the following cases:
  • if the procedure does not exist.
  • if a thread with the same name is currently running.

Forbidden processes

Caution: The following processes cannot be run in the threads:
Caution: it is not allowed to handle the interface (windows, controls, etc.) 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, etc.) called by ExecuteMainThread,
  • the event "Request for refreshing the display" of a window run by RequestRefreshUI.
Business / UI classification : Neutral code
Component : wd250vm.dll
Minimum version required
  • Version 9
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24 Jan. 2019