Programming C++Builder What is Service Threads and Service Threads Examples in C++Builder
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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 TService OnExecute 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.

Example: 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.

1. Choose File|New|Other and double-click Service Application in the New Items dialog. The Service1 window appears.
2. In you unit's header file, 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:

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

3. In the .cpp file for your unit, create a global variable for a TSparkyThread instance:

TSparkyThread *SparkyThread;

4. Add the following code to the .cpp file for the TSparkyThread constructor:

__fastcall TSparkyThread::TSparkyThread(bool CreateSuspended)
        : TThread(CreateSuspended)
{
}

5. Add the following code to the .cpp file for the TSparkyThread Execute method (the thread function):

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

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

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

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

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

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

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

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

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.


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