簡介服務物件讀取器執行緒 (POS for .NET v1.14 SDK 文件)
大部分的服務物件都必須能夠藉由啟動個別的硬體讀取器執行緒，以非同步方式回應硬體事件。 服務物件是服務點應用程式與硬體之間的連結。 因此，服務物件必須從相關聯的硬體讀取資料，同時仍可供應用程式使用。
本節示範實作多執行緒服務物件所需程式碼的其中一種方式。
需求
若要編譯此程式碼，應用程式必須包含 System.Threading 命名空間的參考。
下列範例會實作可由 Service Object 實作使用的執行緒協助程式類別，但不會自行編譯或執行。
示範
此範例示範服務物件如何使用執行緒功能，以非同步方式支援監視硬體事件。 範例程式碼會實作執行緒協助程式類別，可用來將基本執行緒支援新增至服務物件。
若要使用本節中提供的執行緒協助程式類別，您必須建立衍生自 ServiceObjectThreadHelper 的類別，其包含在下列程式碼中，並實作下列方法：
ServiceObjectThreadOpen 初始化完成後，會從執行緒協助程式類別的 OpenThread 方法呼叫這個方法。 在這裡實作任何硬體特定的初始化程式碼。 這個方法是虛擬的。 預設實作只會傳回。
ServiceObjectThreadClose 執行緒協助程式物件終止其執行緒或呼叫 Dispose 方法時，應該用來釋放與裝置相關的任何非受控控制代碼或其他資源時，就會呼叫這個方法。 這個方法是虛擬的。 預設實作只會傳回。
ServiceObjectProcedure 所有初始化已完成而且執行緒已成功啟動後，就會叫用這個方法。 這個方法是抽象的，必須在衍生自執行緒協助程式類別的類別中實作。 ServiceObjectProcedure 方法會採用單一引數 ManualEvent 控制代碼。 設定此控制代碼時，執行緒程式必須結束。 這是藉由在 while 迴圈內呼叫 ManualEvent.WaitOne 來完成。 例如：
while (true) { // Wait for a hardware event or the thread stop event. // Test to see if the thread terminated event is set and // exit the thread if so. if (ThreadStopEvent.WaitOne(0, false)) { break; } // The thread is not terminating, so it must be a // a hardware event. }
範例
using System;
using System.Threading;
using Microsoft.PointOfService;
namespace Samples.ServiceObjects.Advanced
{
// The following code implements a thread helper class.
// This class may be used by other Point Of Service
// samples which may require a separate thread for monitoring
// hardware.
public abstract class ServiceObjectThreadHelper : IDisposable
{
// The thread object which will wait for data from the POS
// device.
private Thread ReadThread;
// These events signal that the thread is starting or stopping.
private AutoResetEvent ThreadTerminating;
private AutoResetEvent ThreadStarted;
// Keeps track of whether or not a thread should
// be running.
bool ThreadWasStarted;
public ServiceObjectThreadHelper()
{
// Create events to signal the reader thread.
ThreadTerminating = new AutoResetEvent(false);
ThreadStarted = new AutoResetEvent(false);
ThreadWasStarted = false;
// You need to handle the ApplicationExit event so
// that you can properly clean up the thread.
System.Windows.Forms.Application.ApplicationExit +=
new EventHandler(Application_ApplicationExit);
}
~ServiceObjectThreadHelper()
{
Dispose(true);
}
public virtual void ServiceObjectThreadOpen()
{
return;
}
public virtual void ServiceObjectThreadClose()
{
return;
}
// This is called when the thread starts successfully and
// will be run on the new thread.
public abstract void ServiceObjectThreadProcedure(
AutoResetEvent ThreadStopEvent);
private bool IsDisposed = false;
protected virtual void Dispose(bool disposing)
{
if (!IsDisposed)
{
try
{
if (disposing == true)
{
CloseThread();
}
}
finally
{
IsDisposed = true;
}
}
}
public void Dispose()
{
Dispose(true);
// This object has been disposed of, so no need for
// the GC to call the finalization code again.
GC.SuppressFinalize(this);
}
public void OpenThread()
{
try
{
// Check to see if this object is still valid.
if (IsDisposed)
{
// Throw system exception to indicate that
// the object has already been disposed.
throw new ObjectDisposedException(
"ServiceObjectSampleThread");
}
// In case the application has called OpenThread
// before calling CloseThread, stop any previously
// started thread.
SignalThreadClose();
ServiceObjectThreadOpen();
// Reset event used to signal the thread to quit.
ThreadTerminating.Reset();
// Reset the event that used by the thread to signal
// that it has started.
ThreadStarted.Reset();
// Create the thread object and give it a name. The
// method used here, ThreadMethod, is a wrapper around
// the actual thread procedure, which will be run in
// the threading object provided by the Service
// Object.
ReadThread = new Thread(
new ThreadStart(ThreadMethod));
// Set the thread background mode.
ReadThread.IsBackground = false;
// Finally, attempt to start the thread.
ReadThread.Start();
// Wait for the thread to start, or until the time-out
// is reached.
if (!ThreadStarted.WaitOne(3000, false))
{
// If the time-out was reached before the event
// was set, then throw an exception.
throw new PosControlException(
"Unable to open the device for reading",
ErrorCode.Failure);
}
// The thread has started successfully.
ThreadWasStarted = true;
}
catch (Exception e)
{
// If an error occurred, be sure the new thread is
// stopped.
CloseThread();
// Re-throw to let the application handle the
// failure.
throw;
}
}
private void SignalThreadClose()
{
if(ThreadTerminating != null && ThreadWasStarted)
{
// Tell the thread to terminate.
ThreadTerminating.Set();
// Give the thread a few seconds to end.
ThreadStarted.WaitOne(10000, false);
// Mark the thread as being terminated.
ThreadWasStarted = false;
}
}
public void CloseThread()
{
// Signal the thread that it should stop.
SignalThreadClose();
// Call back into the SO for any cleanup.
ServiceObjectThreadClose();
}
private void Application_ApplicationExit(
object sender,
EventArgs e)
{
SignalThreadClose();
}
// This is the method run on the new thread. First it signals
// the caller indicating that the thread has started
// correctly. Next, it calls the service object's thread
// method which will loop waiting for data or a signal
// to close.
private void ThreadMethod()
{
try
{
// Set the event to indicate that the thread has
// started successfully.
ThreadStarted.Set();
// Call into the thread procedure defined by the
// Service Object.
ServiceObjectThreadProcedure(ThreadTerminating);
// Signal that the thread procedure is exiting.
ThreadStarted.Set();
}
catch (Exception e)
{
Logger.Info("ServiceObjectThreadHelper",
"ThreadMethod Exception = " + e.ToString());
throw;
}
}
}
}
