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POHow terminate a thread?
 

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  1. POHow terminate a thread?
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    <p>My usual setup for a thread is a while loop and inside the while loop do two things:</p> <ul> <li>do some work</li> <li>Suspend, until resumed from outside</li> </ul> <pre><code>procedure TMIDI_Container_Publisher.Execute; begin Suspend; while not Terminated do begin FContainer.Publish; if not Terminated then Suspend; end; // if end; // Execute // </code></pre> <p>This works fine. To terminate the code I use:</p> <pre><code>destructor TMIDI_Container_Publisher.Destroy; begin Terminate; if Suspended then Resume; Application.ProcessMessages; Self.WaitFor; inherited Destroy; end; // Destroy // </code></pre> <p>This Destroy works fine in Windows 7 but hangs in XP. The problem seems to be the WaitFor but when I remove this the code hangs in the <code>inherited Destroy</code>.</p> <p>Anybody ideas what is wrong?</p> <hr> <p>Update 2011/11/02 Thanks to you all for your help. Remy Labeau came with a code example to avoid Resume/Suspend at all. I'll implement his suggestion in my programs from now on. For this specific case I was inspired by the suggestion of CodeInChaos. Just create a thread, let it do the publish in the Execute and forget about it. I used Remy's example to rewrite one of my timers. I post this implementation below.</p> <pre><code>unit Timer_Threaded; interface uses Windows, MMSystem, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, SyncObjs, Timer_Base; Type TTask = class (TThread) private FTimeEvent: TEvent; FStopEvent: TEvent; FOnTimer: TNotifyEvent; public constructor Create; destructor Destroy; override; procedure Execute; override; procedure Stop; procedure ProcessTimedEvent; property OnTimer: TNotifyEvent read FOnTimer write FOnTimer; end; // Class: TWork // TThreadedTimer = class (TBaseTimer) private nID: cardinal; FTask: TTask; protected procedure SetOnTimer (Task: TNotifyEvent); override; procedure StartTimer; override; procedure StopTimer; override; public constructor Create; override; destructor Destroy; override; end; // Class: TThreadedTimer // implementation var SelfRef: TTask; // Reference to the instantiation of this timer procedure TimerUpdate (uTimerID, uMessage: cardinal; dwUser, dw1, dw2: cardinal); stdcall; begin SelfRef.ProcessTimedEvent; end; // TimerUpdate // {******************************************************************* * * * Class TTask * * * ********************************************************************} constructor TTask.Create; begin FTimeEvent := TEvent.Create (nil, False, False, ''); FStopEvent := TEvent.Create (nil, True, False, ''); inherited Create (False); Self.Priority := tpTimeCritical; end; // Create // destructor TTask.Destroy; begin Stop; FTimeEvent.Free; FStopEvent.Free; inherited Destroy; end; // Destroy // procedure TTask.Execute; var two: TWOHandleArray; h: PWOHandleArray; ret: DWORD; begin h := @two; h [0] := FTimeEvent.Handle; h [1] := FStopEvent.Handle; while not Terminated do begin ret := WaitForMultipleObjects (2, h, FALSE, INFINITE); if ret = WAIT_FAILED then Break; case ret of WAIT_OBJECT_0 + 0: if Assigned (OnTimer) then OnTimer (Self); WAIT_OBJECT_0 + 1: Terminate; end; // case end; // while end; // Execute // procedure TTask.ProcessTimedEvent; begin FTimeEvent.SetEvent; end; // ProcessTimedEvent // procedure TTask.Stop; begin Terminate; FStopEvent.SetEvent; WaitFor; end; // Stop // {******************************************************************* * * * Class TThreaded_Timer * * * ********************************************************************} constructor TThreadedTimer.Create; begin inherited Create; FTask := TTask.Create; SelfRef := FTask; FTimerName := 'Threaded'; Resolution := 2; end; // Create // // Stop the timer and exit the Execute loop Destructor TThreadedTimer.Destroy; begin Enabled := False; // stop timer (when running) FTask.Free; inherited Destroy; end; // Destroy // procedure TThreadedTimer.SetOnTimer (Task: TNotifyEvent); begin inherited SetOnTimer (Task); FTask.OnTimer := Task; end; // SetOnTimer // // Start timer, set resolution of timesetevent as high as possible (=0) // Relocates as many resources to run as precisely as possible procedure TThreadedTimer.StartTimer; begin nID := TimeSetEvent (FInterval, FResolution, TimerUpdate, cardinal (Self), TIME_PERIODIC); if nID = 0 then begin FEnabled := False; raise ETimer.Create ('Cannot start TThreaded_Timer'); end; // if end; // StartTimer // // Kill the system timer procedure TThreadedTimer.StopTimer; var return: integer; begin if nID &lt;&gt; 0 then begin return := TimeKillEvent (nID); if return &lt;&gt; TIMERR_NOERROR then raise ETimer.CreateFmt ('Cannot stop TThreaded_Timer: %d', [return]); end; // if end; // StopTimer // end. // Unit: MSC_Threaded_Timer // unit Timer_Base; interface uses Windows, MMSystem, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs; type TCallBack = procedure (uTimerID, uMessage: UINT; dwUser, dw1, dw2: DWORD); ETimer = class (Exception); {$M+} TBaseTimer = class (TObject) protected FTimerName: string; // Name of the timer FEnabled: boolean; // True= timer is running, False = not FInterval: Cardinal; // Interval of timer in ms FResolution: Cardinal; // Resolution of timer in ms FOnTimer: TNotifyEvent; // What to do when the hour (ms) strikes procedure SetEnabled (value: boolean); virtual; procedure SetInterval (value: Cardinal); virtual; procedure SetResolution (value: Cardinal); virtual; procedure SetOnTimer (Task: TNotifyEvent); virtual; protected procedure StartTimer; virtual; abstract; procedure StopTimer; virtual; abstract; public constructor Create; virtual; destructor Destroy; override; published property TimerName: string read FTimerName; property Enabled: boolean read FEnabled write SetEnabled; property Interval: Cardinal read FInterval write SetInterval; property Resolution: Cardinal read FResolution write SetResolution; property OnTimer: TNotifyEvent read FOnTimer write SetOnTimer; end; // Class: HiResTimer // implementation constructor TBaseTimer.Create; begin inherited Create; FEnabled := False; FInterval := 500; Fresolution := 10; end; // Create // destructor TBaseTimer.Destroy; begin inherited Destroy; end; // Destroy // // SetEnabled calls StartTimer when value = true, else StopTimer // It only does so when value is not equal to the current value of FEnabled // Some Timers require a matching StartTimer and StopTimer sequence procedure TBaseTimer.SetEnabled (value: boolean); begin if value &lt;&gt; FEnabled then begin FEnabled := value; if value then StartTimer else StopTimer; end; // if end; // SetEnabled // procedure TBaseTimer.SetInterval (value: Cardinal); begin FInterval := value; end; // SetInterval // procedure TBaseTimer.SetResolution (value: Cardinal); begin FResolution := value; end; // SetResolution // procedure TBaseTimer.SetOnTimer (Task: TNotifyEvent); begin FOnTimer := Task; end; // SetOnTimer // end. // Unit: MSC_Timer_Custom // </code></pre>
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    1. COThe inherited destroy calls WaitFor too. Don't know your problem but you aren't supposed to use Suspend or Resume. I'd use events to pause threads. What does the ProcessMessages do?
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      1. POHow terminate a thread?
      1. USDavid Heffernan
    2. COWe don't know what's in `inherited Destroy`, so it's hard to say. But as a general practice, `Suspend` and `Resume` shouldn't be used. It's better to use a synchronization object (try `SyncObjs.TSimpleEvent`) and have your thread wait on it.
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      1. POHow terminate a thread?
      1. USMason Wheeler
    3. CO@Mason Since we are calling `Terminate`, `Resume`, `Suspend`, `WaitFor` etc., I think we can guess that `inherited Destroy` is `TThread.Destroy`. But you are quite right about `Suspend`, `Resume` and events.
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      1. POHow terminate a thread?
      1. USDavid Heffernan
 

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