CAMThread Class

CAMThread is an abstract class, a worker thread class that provides creation, synchronization, and communication with a worker thread. The worker thread can be accessed from several client threads. The class provides member functions to create the thread, pass commands to it, and wait for it to exit.

Use a CCritSec object to ensure that only one thread can make a request at a time. Use two CAMEvent objects: one to signal to the worker that a request is outstanding, and the other to signal to the client thread that the request has been completed. A nonblocking CAMThread::CheckRequest member function allows the worker thread to check for new requests while working asynchronously.

Derive from this class to provide your own thread member function. You might also want to provide type-safe signaling member functions that package parameters and return values using the CAMThread::CallWorker member function.

Thread creation is independent of object creation. Create a member variable derived from CAMThread, and then use the member functions to start and stop the thread when needed.

Data Members

Name	Description
m_AccessLock	Critical section object that locks access by client threads.
m_WorkerLock	Critical section object that locks access to shared objects.

Member Functions

Name	Description
CallWorker	Makes a request to the worker thread.
CAMThread	Constructs a CAMThread object.
CheckRequest	Determines if there is an outstanding request. This is a nonblocking member function.
Close	Blocks until the thread has exited and released its resources.
Create	Starts the thread running.
GetRequest	Blocks until the next request is made and then returns a DWORD value.
GetRequestHandle	Returns an event handle.
GetRequestParam	Returns the latest request.
InitialThreadProc	Retrieves a this pointer. Carry out this member function before calling the CAMThread::ThreadProc member function.
Reply	Returns a DWORD value to the requesting thread and releases it, signaling completion of the request.
ThreadExists	Determines whether a thread exists or has exited.
ThreadProc	Indicates a pure virtual member function that is called on the worker thread.

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CAMThread::CallWorker

CAMThread Class

Makes a request to the worker thread and blocks for a response.

DWORD CallWorker(
  DWORD dw
  );

Parameters

dw

Derived class defines the meaning of the parameter.

Return Values

Returns a value that is defined by the derived class.

Remarks

This member function uses a CCritSec object to ensure that only one request is made at a time. It is therefore not valid to call the CAMThread::CallWorker member function from the thread itself or from any member function that is executing in the context of the thread.

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CAMThread::CAMThread

CAMThread Class

Constructs a CAMThread object.

CAMThread( );

Return Values

No return value.

Remarks

Creates a CAMThread object but does not create an actual thread. You call the CAMThread::Create member function to create a thread.

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CAMThread::CheckRequest

CAMThread Class

Determines if there is an outstanding request. This is a nonblocking member function.

BOOL CheckRequest(
  DWORD *pParam
  );

Parameters

pParam

Parameter that assumes the value passed by the last call to the CAMThread::CallWorker member function.

Return Values

Returns TRUE if an outstanding request is still active, or FALSE is no request is active.

Remarks

If there is an outstanding request, the requesting thread will block until the CAMThread::GetRequest member function is called. The request remains outstanding (that is, this member function continues to return TRUE) until either the CAMThread::Reply or CAMThread::GetRequest member function is called.

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CAMThread::Close

CAMThread Class

Blocks until the thread has exited and released its resources.

void Close(void);

Return Values

No return value.

Remarks

You must instruct the thread to exit by some other means; for example, call the CAMThread::CallWorker member function with a request that is interpreted by the derived class to mean complete and exit.

If the thread is still running when the CAMThread object is destroyed, the CAMThread::Close member function is called internally.

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CAMThread::Create

CAMThread Class

Starts the thread running.

BOOL Create(void);

Return Values

Returns TRUE if the thread started successfully, or FALSE if the thread is already running.

Remarks

This member function creates the thread and calls the CAMThread::ThreadProc member function from the derived class.

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CAMThread::GetRequest

CAMThread Class

Blocks until the next request is made.

DWORD GetRequest( );

Return Values

Returns a value that is defined by the derived class.

Remarks

This member function blocks the requesting thread until the CAMThread::Reply function is called.

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CAMThread::GetRequestHandle

CAMThread Class

Returns an event handle for performance improvements.

HANDLE GetRequestHandle( ) const;

Return Values

Returns an event handle.

Remarks

To use the Microsoft Win32 WaitForMultipleObjects function, you will need this handle in the thread's wait list or the thread will not be responsive.

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CAMThread::GetRequestParam

CAMThread Class

Returns the most recent request.

DWORD GetRequestParam( ) const;

Return Values

Returns a DWORD value that indicates the request made previously by the CAMThread::GetRequest member function.

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CAMThread::InitialThreadProc

CAMThread Class

Receives a this pointer and calls the CAMThread::ThreadProc member function.

DWORD InitialThreadProc(
  LPVOID pv
  );

Parameters

pv

The this pointer.

Return Values

Returns the DWORD returned by CAMThread::ThreadProc. This DWORD is not defined by this class.

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CAMThread::Reply

CAMThread Class

Returns a DWORD value to the requesting thread and releases it, signaling completion of the request.

void Reply(
  DWORD dw
  );

Parameters

dw

Value returned by the CAMThread::CallWorker member function on the client side.

Return Values

No return value.

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CAMThread::ThreadExists

CAMThread Class

Determines whether the thread has been created and has not yet exited.

BOOL ThreadExists( );

Return Values

Returns TRUE if the thread exists and hasn't exited, or FALSE if the thread doesn't exist.

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CAMThread::ThreadProc

CAMThread Class

Overridden member function in which to implement a thread.

virtual DWORD ThreadProc( );

Return Values

The meaning of this return value is not defined by the CAMThread class.

Remarks

The thread calls this member function upon startup. Derived classes must override this member function. When this member function returns, the thread terminates. This member function is protected.

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