ThreadExecute (Function)

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Characteristics of a thread created in WLanguage
Thread and HFSQL
Characteristics of WLanguage procedure
Life cycle of a thread
Error management
Forbidden processes
Stopping a thread

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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.

Reminder: A thread is a process run in parallel with the current application (main thread). This allows you to run a task in the background (e.g. backup, etc.).

Versions 15 and later

This function is now available for Android applications.

New in version 15

This function is now available for Android applications.

Versions 18 and later

This function is now available in Android Widget mode.

New in version 18

This function is now available in Android Widget mode.

Versions 19 and later

This function is now available for iPhone/iPad applications.

This function is now available for WINDEV applications in Linux.

This function is now available for WEBDEV sites in Linux.

New in version 19

This function is now available for iPhone/iPad applications.

This function is now available for WINDEV applications in Linux.

This function is now available for WEBDEV sites in Linux.

This function is now available for iPhone/iPad applications.

This function is now available for WINDEV applications in Linux.

This function is now available for WEBDEV sites in Linux.

Versions 21 and later

This function is now available in Apple Watch mode.

This function is now available in Universal Windows 10 App mode.

New in version 21

This function is now available in Apple Watch mode.

This function is now available in Universal Windows 10 App mode.

This function is now available in Apple Watch mode.

This function is now available in Universal Windows 10 App mode.

Example

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 as parameter of a query
PROCEDURE pExecQry(sDate)
IF HExecuteQuery(Del_Date, hQueryDefault, sDate) = False THEN
Error(HErrorInfo())
ELSE
HReadFirst(Del_Date)
END

Syntax

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
threadWaitForStart
New in version 18
threadWaitForStart
threadWaitForStart Waits for the actual start of the thread before continuing the execution.
This constant is not available.
Versions 16 and later
threadGlobalContext
New in version 16
threadGlobalContext
threadGlobalContext 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.
This constant is not available.
threadFullCopyHFSQLContext
(Default value) Triggers the immediate copy of the current HFSQL context.
Recommended if the thread must take into account the current positions in the files and queries of caller context.
This constant is not available.
Versions 20 and later
threadLightCopyHFSQLContext
New in version 20
threadLightCopyHFSQLContext
threadLightCopyHFSQLContext Triggers the immediate copy of a part of the 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.
This constant is not available.
threadNormal Starts the thread in normal mode. The HFSQL context is copied the first time an HFSQL feature is used.
Versions 26 and later
threadSecure
New in version 26
threadSecure
threadSecure Starts a thread in secure mode. In this mode, an exception will be thrown:
if the thread accesses the controls at runtime,
if ThreadStop is used.
When the window that triggered the thread is closed, a request to stop the thread is generated (but the thread continues to run after the window is closed).

<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).

Versions 25 and later

Declaring and executing a Thread variable Hide the details

<Result> = ThreadExecute(<WLanguage procedure> [, <Parameter 1> [... [, <Parameter N>]]] [, <Options>])

<Result>: Thread variable

Thread variable corresponding to the thread executed.

<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).

<Options>: Optional constant

Mode for starting the thread.
threadWaitForStart Waits for the actual start of the thread before continuing the execution.
This constant is not available.
threadGlobalContext 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.
This constant is not available.
threadFullCopyHFSQLContext
(Default value) Triggers the immediate copy of the current HFSQL context.
Recommended if the thread must take into account the current positions in the files and queries of caller context.
This constant is not available.
threadLightCopyHFSQLContext Triggers the immediate copy of a part of the 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.
This constant is not available.
threadNormal Starts the thread in normal mode. The HFSQL context is copied the first time an HFSQL feature is used.
Versions 26 and later
threadSecure
New in version 26
threadSecure
threadSecure Starts a thread in secure mode. In this mode, an exception will be thrown:
if the thread accesses the controls at runtime,
if ThreadStop is used.
When the window that triggered the thread is closed, a request to stop the thread is generated (but the thread continues to run after the window is closed).

New in version 25

Declaring and executing a Thread variable Hide the details

<Result> = ThreadExecute(<WLanguage procedure> [, <Parameter 1> [... [, <Parameter N>]]] [, <Options>])

<Result>: Thread variable

Thread variable corresponding to the thread executed.

<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).

<Options>: Optional constant

Mode for starting the thread.
threadWaitForStart Waits for the actual start of the thread before continuing the execution.
This constant is not available.
threadGlobalContext 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.
This constant is not available.
threadFullCopyHFSQLContext
(Default value) Triggers the immediate copy of the current HFSQL context.
Recommended if the thread must take into account the current positions in the files and queries of caller context.
This constant is not available.
threadLightCopyHFSQLContext Triggers the immediate copy of a part of the 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.
This constant is not available.
threadNormal Starts the thread in normal mode. The HFSQL context is copied the first time an HFSQL feature is used.
Versions 26 and later
threadSecure
New in version 26
threadSecure
threadSecure Starts a thread in secure mode. In this mode, an exception will be thrown:
if the thread accesses the controls at runtime,
if ThreadStop is used.
When the window that triggered the thread is closed, a request to stop the thread is generated (but the thread continues to run after the window is closed).

Declaring and executing a Thread variable Hide the details

<Result> = ThreadExecute(<WLanguage procedure> [, <Parameter 1> [... [, <Parameter N>]]] [, <Options>])

<Result>: Thread variable

Thread variable corresponding to the thread executed.

<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).

<Options>: Optional constant

Mode for starting the thread.
threadWaitForStart Waits for the actual start of the thread before continuing the execution.
This constant is not available.
threadGlobalContext 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.
This constant is not available.
threadFullCopyHFSQLContext
(Default value) Triggers the immediate copy of the current HFSQL context.
Recommended if the thread must take into account the current positions in the files and queries of caller context.
This constant is not available.
threadLightCopyHFSQLContext Triggers the immediate copy of a part of the 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.
This constant is not available.
threadNormal Starts the thread in normal mode. The HFSQL context is copied the first time an HFSQL feature is used.
Versions 26 and later
threadSecure
New in version 26
threadSecure
threadSecure Starts a thread in secure mode. In this mode, an exception will be thrown:
if the thread accesses the controls at runtime,
if ThreadStop is used.
When the window that triggered the thread is closed, a request to stop the thread is generated (but the thread continues to run after the window is closed).

Versions 25 and later

Executing a thread already described (Thread variable) Hide the details

<Result> = ThreadExecute(<Thread>)

<Result>: Thread variable

Thread variable corresponding to the thread executed.

<Thread>: Thread variable

Name of the Thread variable corresponding to the thread to execute.
Caution: If the thread is already being executed or has already been executed, a WLanguage error will appear.

New in version 25

Executing a thread already described (Thread variable) Hide the details

<Result> = ThreadExecute(<Thread>)

<Result>: Thread variable

Thread variable corresponding to the thread executed.

<Thread>: Thread variable

Name of the Thread variable corresponding to the thread to execute.
Caution: If the thread is already being executed or has already been executed, a WLanguage error will appear.

Executing a thread already described (Thread variable) Hide the details

<Result> = ThreadExecute(<Thread>)

<Result>: Thread variable

Thread variable corresponding to the thread executed.

<Thread>: Thread variable

Name of the Thread variable corresponding to the thread to execute.
Caution: If the thread is already being executed or has already been executed, a WLanguage error will appear.

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, 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 Management of HFSQL contexts.

Example:

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). For more details, see Assisted management of HFSQL errors.
Write operations and assignments in a thread: If values are written or assigned in a thread, the other running threads 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.

The calls to Info, Error, ... do not lock the threads currently run.

Remark: The parameters passed to the procedure are passed by value and not by reference.

For more details on how to open a window from a secondary thread, see Opening a window in a secondary thread.

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.

Error management

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:

opening windows with WLanguage functions such as Open, Use, Close, ... A specific management mode must be implemented if some windows must be handled in threads (rare case). For more details, see Opening a window in a secondary thread.
managing events.
multitask.
managing timers.

Caution: UI elements (windows, controls, etc.) cannot be manipulated in a secondary thread.
When a secondary thread must interact with the user or update the UI, 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.

Stopping a thread

ThreadStop is not available in Android.

The full stop of the must be performed by the thread itself, at the end of the WLanguage procedure called by ThreadExecute.

Example:

ThreadExecute("th", threadNormal, ProcThread)

PROCEDURE ProcThread
bThreadAlive is boolean = True
WHILE bThreadAlive

// ... Process

// Test the end condition of the thread
IF <THREAD END CONDITION> THEN
bThreadAlive = False
END
END

Business / UI classification: Neutral code

Component: wd260vm.dll