Service Threads

Each service has its own thread (TServiceThread), so if your service application implements more than one service you must ensure that the implementation of your services is thread-safe. TServiceThread is designed so that you can implement the service in the TServiceOnExecute event handler. The service thread has its own Execute method which contains a loop that calls the service's OnStart and OnExecute handlers before processing new requests.

Because service requests can take a long time to process and the service application can receive simultaneous requests from more than one client, it is more efficient to spawn a new thread (derived from TThread, not TServiceThread) for each request and move the implementation of that service to the new thread's Execute method. This allows the service thread's Execute loop to process new requests continually without having to wait for the service's OnExecute handler to finish. The following example demonstrates.

Note: This service beeps every 500 milliseconds from within the standard thread. It handles pausing, continuing, and stopping of the thread when the service is told to pause, continue, or stop.

To create the example:

Choose FileNewOther and double-click Service Application in the New Items dialog. The Service1 window appears.
In the interface section of your unit, declare a new descendant of TThread named TSparkyThread. This is the thread that does the work for your service. The declaration should appear as follows:

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TSparkyThread = class(TThread)
  public
    procedure Execute; override;
end;

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class TSparkyThread : public TThread
{
private:
protected:
  void __fastcall Execute();
public:
__fastcall TSparkyThread(bool CreateSuspended);
};

In the implementation section of your unit, create a global variable for a TSparkyThread instance:

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var
  SparkyThread: TSparkyThread;

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TSparkyThread *SparkyThread;// Add this code as the constructor
__fastcall TSparkyThread::TSparkyThread(bool CreateSuspended)
: TThread(CreateSuspended)
{
}

In the implementation section for the TSparkyThread Execute method (the thread function), add the following code:

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procedure TSparkyThread.Execute;
begin
  while not Terminated do
  begin
    Beep;
    Sleep(500);
  end;
end;

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void __fastcall TSparkyThread::Execute()
{
  while (!Terminated)
  {
    Beep();
    Sleep(500);
  }
}

Select the Service window (Service1), and double-click the OnStart event in the Object Inspector. Add the following OnStart event handler:

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procedure TService1.Service1Start(Sender: TService; var Started: Boolean);
begin
  SparkyThread := TSparkyThread.Create(False);
  Started := True;
end;

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void __fastcall TService1::Service1Start(TService *Sender, bool &Started)
{
  SparkyThread = new TSparkyThread(false);
  Started = true;
}

Double-click the OnContinue event in the Object Inspector. Add the following OnContinue event handler:

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procedure TService1.Service1Continue(Sender: TService; var Continued: Boolean);
begin
  SparkyThread.Resume;
  Continued := True;
end;

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void __fastcall TService1::Service1Continue(TService *Sender, bool &Continued)
{
  SparkyThread->Resume();
  Continued = true;
}

Double-click the OnPause event in the Object Inspector. Add the following OnPause event handler:

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procedure TService1.Service1Pause(Sender: TService; var Paused: Boolean);
begin
  SparkyThread.Suspend;
  Paused := True;
end;

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void __fastcall TService1::Service1Pause(TService *Sender, bool &Paused)
{
  SparkyThread->Suspend();
  Paused = true;
}

Finally, double-click the OnStop event in the Object Inspector and add the following OnStop event handler:

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procedure TService1.Service1Stop(Sender: TService; var Stopped: Boolean);
begin
  SparkyThread.Terminate;
  Stopped := True;
end;

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void __fastcall TService1::Service1Stop(TService *Sender, bool &Stopped)
{
  SparkyThread->Terminate();
  Stopped = true;
}

When developing server applications, choosing to spawn a new thread depends on the nature of the service being provided, the anticipated number of connections, and the expected number of processors on the computer running the service.