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FRECLIEN - Client of Free-threaded Server |
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The FRECLIEN sample spawns multiple threads to create and use the COBall COM object provided by the FRESERVE free-threaded server. COBall object itself spawns no threads; it passively responds to IBall interface requests from multiple client threads. The FRECLIEN client creates and controls one COBall object through the IBall interface that the object exposes. As three of FRECLIEN's threads move the ball through calls to IBall::Move, the remaining main thread uses a system timer to obtain timed updates of the COBall object's position, size, and color. This main thread uses that data, obtained by calling the IBall::GetBall method, to display graphical snapshot images of the ball in the client's main window.
As explained in the FRESERVE sample, the COBall object internally updates its color property to reflect the last thread that called the object's Move method. The display thread uses this data for each ball image it displays. As the ball moves, it changes color to reflect the changing threads that move the ball. As the ball moves, it also leaves a trail that provides a striking visual history of these passing threads. This trail demonstrates that, with COM's free threading model, all threads that make interface requests to the same object access the object on the different calling threads. Each different color of the single ball object represents a different calling thread. Since the display thread is asynchronous with respect to the ball-moving threads, there is no guarantee that the display trail will include a record of every thread that moved the ball. Based on thread scheduling and on the load of other applications running, not all threads that move the ball are caught in the act by the display thread.
This free threading model is in contrast to the apartment model presented in the APTSERVE and APTCLIEN samples. In apartment model threading, each COM object is associated with an single-threaded apartment. Calls from multiple client threads are switched by COM to the thread of the apartment that owns the object. Only one thread, the object's apartment thread, is permitted to execute the methods of the object. This provides a serialization of access to the object's data.
For functional descriptions and a tutorial code tour of FRECLIEN, see the Code Tour section in FRECLIEN.HTM. For details on the external user operation of FRECLIEN, see both the Usage and Operation sections in FRECLIEN.HTM. To read FRECLIEN.HTM, run TUTORIAL.EXE in the main tutorial directory and click the FRECLIEN lesson in the table of lessons. You can also achieve the same thing by clicking the FRECLIEN.HTM file after locating the main tutorial directory in the Windows Explorer. See also FRESERVE.HTM in the main tutorial directory for more details on how FRESERVE works and exposes its services to FRECLIEN. You must build the FRESERVE DLL before building FRECLIEN. The makefile for FRESERVE automatically registers that server in the system registry, so you must build FRESERVE before attempting to run FRECLIEN.
For details on setting up your system to build and test the code samples in this COM Tutorial series, see TUTORIAL.HTM. The supplied MAKEFILE is Microsoft NMAKE-compatible. To create a debug build, issue the NMAKE command in the Command Prompt window.
FRECLIEN is an application that you can execute directly from Windows in the normal manner or from the Command Prompt window. No command line parameters are recognized by FRECLIEN. FRECLIEN currently requires the free-threading facilities provided in more recent releases of COM such as found in version 4.0 and later releases of the Windows NT operating system. The Windows 95 operating system does not currently support free threading, so FRECLIEN will not run on it. However, a DCOM95 add-on to Win95 will permit the FRECLIEN/FRESERVE samples to run on Win95. DCOM95 is currently nearing release.
The client sample and other related samples must be compiled before you can run the client. For more details on building the samples, see Building the Code Samples.
If you have already built the appropriate samples, FRECLIEN.EXE is the client executable to run for this sample.
The FRECLIEN.EXE application provides the user interface for this lesson. It exercises the associated, but independent, FRESERVE.DLL to graphically illustrate the free threading model. As the ball image created by FRECLIEN moves, it leaves a trail. This trail shows a history of the various threads that have executed the COBall object's Move method.
Here is a summary of operation from the standpoint of FRECLIEN.EXE as a COM client of the FRESERVE.DLL COM server.
There is a minimal menu in FRECLIEN. All the operation is automatic. The main application window's client area is used for visual display of the moving ball.
Menu Selection: File/Exit
Exits FRECLIEN.
Menu Selection: Help/FRECLIEN Tutorial
Opens the FRECLIEN.HTM tutorial file in the Web browser.
Menu Selection: Help/FRESERVE Tutorial
Opens the FRESERVE.HTM tutorial file in the Web browser.
Menu Selection: Help/Read Source File
Displays the Open common dialog box so you can open a source file from this lesson or another one in the Windows Notepad.
Menu Selection: Help/About FRECLIEN
Displays the About dialog box for this application, a standard part of this series of code samples. The code illustrates how to program the use of the CAboutBox class provided by APPUTIL.LIB.
Files Description
FRECLIEN.TXT Short sample description.
MAKEFILE The generic makefile for building the code sample
application of this tutorial lesson.
FRECLIEN.H The include file for the FRECLIEN application.
Contains
class declarations, function prototypes, and resource
identifiers.
FRECLIEN.CPP The main implementation file for FRECLIEN.EXE. Has
WinMain
and CMainWindow implementation, as well as the main
menu
dispatching.
FRECLIEN.RC The application resource definition file.
FRECLIEN.ICO The application icon resource.
GUIBALL.H The class declaration for the CGuiBall C++ class.
GUIBALL.CPP Implementation file for the CGuiBall C++ class.
FRECLIEN uses many of the utility classes and services provided by APPUTIL. For more details on APPUTIL, study the APPUTIL library source code in the sibling APPUTIL directory and APPUTIL.HTM in the main tutorial directory.
The program logic governing the ball's motion is encapsulated in the COBall object. See the FRESERVE sample and FRESERVE.HTM for details.
The major topics covered in this code tour are:
The main FRECLIEN process initializes COM for free-threaded operation. It does this in the WinMain function. Here is the code from FRECLIEN.CPP.
...
// Call to initialize the COM Library. Use the SUCCEEDED macro
// to detect success. If fail, then exit app with error message.
// Initialize COM here in the main process thread to establish
this
// main thread as the founding member of the multi-threaded
apartment
// of this process. Other worker free-threads will also live in
this
// multi-threaded apartment. The app can have only one such multi-
// threaded apartment but could have a mixed model with other
// single-threaded apartments running. This sample has no other
// single-threaded apartments.
if (SUCCEEDED(CoInitializeEx(NULL, COINIT_MULTITHREADED)))
{
...
... Init application and enter main message loop, etc
...
}
...
The CoInitializeEx function is called with the COINIT_MULTITHREADED flag. This means that COM is initialized to use the free-threading model in FRECLIEN's main message loop thread. Other worker threads will be created and initialized as COINIT_MULTITHREADED. These worker threads will also operate in the free-threaded model on a single instance of FRESERVE's COBall COM object.
FRECLIEN uses a CGuiBall C++ class to encapsulate the data and behavior of the client's graphical user interface (GUI) moving ball.
Here is the declaration of the CGuiBall class from file GUIBALL.H.
class CGuiBall
{
private:
HWND m_hWnd;
IBall* m_pIBall;
COLORREF m_crColor;
// Pointers to thread init data structures.
CThreadInitData m_BallThreadData1;
CThreadInitData m_BallThreadData2;
CThreadInitData m_BallThreadData3;
public:
// Some member variables to store thread ids.
DWORD m_dwBallThread1;
DWORD m_dwBallThread2;
DWORD m_dwBallThread3;
// An array of handles to the ball threads.
HANDLE m_hBallThreads[3];
CGuiBall(void);
~CGuiBall(void);
BOOL Init(HWND hWnd);
void PaintBall(void);
void Restart(void);
void PaintWin(void);
};
The main process thread uses CGuiBall by calling its main public methods: Init, Restart, PaintBall, and PaintWin. Calls through the IBall interface on FRESERVE's COBall object are encapsulated within the methods of CGuiBall. The COBall object is accessed through an IBall interface pointer, m_pIBall, privately held in CGuiBall.
CGuiBall has an Init method in which an instance of FRESERVE's COBall object is created. This Init method also spawns three threads whose sole job is to continuously call COBall::Move to move the ball entity defined in COBall. These three calling threads keep the ball moving while the main display thread continuously paints snapshot images of the moving ball. CGuiBall keeps the identifiers of these three threads. Several CThreadInitData structures are used to create the threads.
Here is the CGuiBall::Init method definition from GUIBALL.CPP.
BOOL CGuiBall::Init(
HWND hWnd)
{
BOOL bOk = FALSE;
HRESULT hr;
if (hWnd)
{
m_hWnd = hWnd;
// Call COM service to create the single COBall instance.
// We are not aggregating it so we ask for its IBall interface
// directly.
hr = CoCreateInstance(
CLSID_DllBall,
NULL,
CLSCTX_INPROC_SERVER,
IID_IBall,
(PPVOID)&m_pIBall);
if (SUCCEEDED(hr))
{
// Now start up 3 client BallThreads that will all try to
move the
// Ball concurrently. They will bring independent
asynchronous life
// to the ball. The separate main process thread displays
the ball.
// These threads (including the main display thread) will
all
// comprise the multi-threaded apartment of the main
process.
// Create Structures for thread initialization.
m_BallThreadData1.m_hWnd = hWnd;
m_BallThreadData1.m_nDelay = BALL_MOVE_DELAY;
m_BallThreadData1.m_pIBall = m_pIBall;
m_BallThreadData2.m_hWnd = hWnd;
m_BallThreadData2.m_nDelay = BALL_MOVE_DELAY;
m_BallThreadData2.m_pIBall = m_pIBall;
m_BallThreadData3.m_hWnd = hWnd;
m_BallThreadData3.m_nDelay = BALL_MOVE_DELAY;
m_BallThreadData3.m_pIBall = m_pIBall;
// Create the ball-moving thread #1.
m_hBallThreads[0] = CreateThread(
0,
0,
(LPTHREAD_START_ROUTINE)
BallThreadProc,
(LPVOID) &m_BallThreadData1,
0,
&m_dwBallThread1);
bOk = (NULL != m_hBallThreads[0]);
if (bOk)
{
// AddRef for the copy handed out to free-thread1.
m_pIBall->AddRef();
// Create the Ball Moving Thread #2.
m_hBallThreads[1] = CreateThread(
0,
0,
(LPTHREAD_START_ROUTINE)
BallThreadProc,
(LPVOID) &m_BallThreadData2,
0,
&m_dwBallThread2);
bOk = (NULL != m_hBallThreads[1]);
if (bOk)
{
// AddRef for the copy handed out to free-thread2.
m_pIBall->AddRef();
// Create the Ball Moving Thread #3.
m_hBallThreads[2] = CreateThread(
0,
0,
(LPTHREAD_START_ROUTINE)
BallThreadProc,
(LPVOID) &m_BallThreadData3,
0,
&m_dwBallThread3);
bOk = (NULL != m_hBallThreads[2]);
if (bOk)
{
// AddRef for the copy handed out to free-thread3.
m_pIBall->AddRef();
}
}
}
}
else
HrMsg(hWnd, TEXT(NOCOMOBJ_ERROR_STR), hr);
if (!bOk)
{
hr = GetLastError();
if (FAILED(hr))
HrMsg(hWnd, TEXT(NOTHREAD_ERROR_STR), hr);
}
}
if (bOk)
{
// Set up the client process to periodically paint the ball
// thru WM_TIMER messages to the main Window proc.
SetTimer(hWnd, 1, BALL_PAINT_DELAY, NULL);
}
return (bOk);
}
CoCreateInstance is called to create an instance of the FRESERVE server's COBall object specified by its CLSID, CLSID_DllBall. This CLSID is defined in BALLGUID.H, located in the sibling INC directory. Because aggregation is not required, CoCreateInstance directly requests the IBall interface, which on return is stored in m_pIBall. The Init method then launches the three moving threads after setting appropriate CThreadInitData structures. This is the CThreadInitData as declared in GUIBALL.H.
// A small utility struct providing an encapsulation of data
needed when
// worker threads are initialized.
struct CThreadInitData
{
HWND m_hWnd;
IBall* m_pIBall;
DWORD m_nDelay;
};
As presented in the previous APTSERVE sample, a pointer to a CThreadInitData structure is passed as an LPARAM to the thread procedure of the newly launched thread. Using this structure, the client's main window handle, an interface pointer to the IBall interface on the COBall object, and a value for the time delay between ball movements are all passed to the new threads. Following the COM contract, the Init method calls m_pIBall->AddRef for each copy of the interface pointer returned to the newly created thread. These AddRef calls are later matched by Release calls in the CGuiBall destructor.
Note that the interface pointer in member m_pIBall is passed from one thread, the main thread, to the newly created thread. This requires no marshaling because both threads are in the same multi-threaded apartment of the process. If the creating thread was in a single-threaded apartment that was creating a new thread in the multi-threaded apartment then explicit marshaling of the passed m_pIBall interface would be required. The CoMarshalInterThreadInterfaceInStream and CoGetInterfaceAndReleaseStream functions are convenient for such explicit runtime marshaling of interfaces between threads within a process.
The m_hBallThreads array holds handles to the created threads. It is used for later calls to WaitForMultipleObjects to ensure an orderly shutdown of the threads before the client program exits. This occurs in the CGuiBall destructor. Here is the destructor from GUIBALL.CPP.
CGuiBall::~CGuiBall(void)
{
BOOL bOk = TRUE;
if (m_pIBall)
{
// Kill the client's app timer for its repaints.
KillTimer(m_hWnd, 1);
// Call down to the server's COBall and tell it to shutdown.
m_pIBall->Move(FALSE);
// Wait for the threads to terminate before closing their
// thread handles.
WaitForMultipleObjects(3, m_hBallThreads, TRUE, INFINITE);
for (size_t i = 0; i<3; i++)
CloseHandle(m_hBallThreads[i]);
// Release for each of the thread copies handed out.
m_pIBall->Release();
m_pIBall->Release();
m_pIBall->Release();
// Do final Release for the main copy held in CGuiBall.
RELEASE_INTERFACE(m_pIBall);
}
}
The main process thread relies on a recurrent system timer's WM_TIMER message. This was set up within the Init method of CGuiBall shown above. These periodic timer messages drive the client's independent asynchronous display process. The timer is killed in the destructor (see above) with the KillTimer call. Each WM_TIMER message sent to the main window procedure is honored by a call to the COBall::GetBall method to obtain the ball's display data. Here is the main window procedure from FRECLIEN.CPP.
LRESULT CMainWindow::WindowProc(
UINT uMsg,
WPARAM wParam,
LPARAM lParam)
{
LRESULT lResult = FALSE;
switch (uMsg)
{
case WM_CREATE:
break;
case WM_MEASUREITEM:
// Get setup for painting text in this window.
{
LPMEASUREITEMSTRUCT lpmis = (LPMEASUREITEMSTRUCT) lParam;
lpmis->itemHeight = m_tm.tmHeight +
m_tm.tmExternalLeading;
lpmis->itemWidth = m_wWidth;
lResult = TRUE;
}
case WM_SIZE:
// Handle a resize of this window.
m_wWidth = LOWORD(lParam);
m_wHeight = HIWORD(lParam);
// Handle a resize of this window.
// Restart the ball from upper left, clear window.
m_pGuiBall->Restart();
break;
case WM_TIMER:
// This is our timed attempt to continuously paint the
moving ball.
// It doesn't move it. Other non-GUI threads move the
virtual ball.
m_pGuiBall->PaintBall();
break;
case WM_COMMAND:
// Dispatch and handle any Menu command messages received.
lResult = DoMenu(wParam, lParam);
break;
case WM_CHAR:
if (wParam == 0x1b)
{
// Exit this app if user hits ESC key.
PostMessage(m_hWnd,WM_CLOSE,0,0);
break;
}
case WM_LBUTTONUP:
case WM_PAINT:
// If something major happened or user clicks or hits key
then
// repaint the whole window.
m_pGuiBall->PaintWin();
break;
case WM_CLOSE:
// The user selected Close on the main window's System menu.
case WM_QUIT:
// If the app is quit by the File/Exit main menu then close
// any associated help windows too.
::WinHelp(m_hWnd, m_szHelpFile, HELP_QUIT, 0);
default:
// Defer all messages NOT handled here to the Default Window
Proc.
lResult = ::DefWindowProc(m_hWnd, uMsg, wParam, lParam);
break;
}
return(lResult);
}
The CGuiBall::PaintBall method is called to paint the ball when the WM_TIMER messages arrive. Other main client application messages of interest are WM_SIZE, WM_PAINT, and WM_LBUTTONUP. For WM_SIZE, if the user resizes the client application's main window, CGuiBall::Restart is called. The WM_SIZE message handler calls COBall::Reset, which relocates the ball to the upper left corner of the window and also resets the ball size. If the user clicks the left mouse button (causing WM_LBUTTONUP) or a general WM_PAINT condition occurs, the window is repainted, but the ball is not reset.
The threads each run the following common thread procedure, BallThreadProc in GUIBALL.CPP.
DWORD WINAPI BallThreadProc(
LPARAM lparam)
{
CThreadInitData* pInitData = (CThreadInitData*) lparam;
DWORD nEndCount = 0;
HRESULT hr;
BOOL bAlive;
// Initialize COM for use by this thread. Tell COM this new
thread
// is another free-threaded thread in the multi-threaded
apartment.
hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);
bAlive = SUCCEEDED(hr);
if (bAlive)
{
// Continuously move the ball while it is still alive.
while (bAlive)
{
// Use system timer to slow down the ball motion to the
range
// of the humanly perceptible.
if (GetTickCount() > nEndCount)
{
// After the delay, call from this thread thru IBall
interface
// to move the ball that lives in the single COBall COM
object.
// Set bAlive flag FALSE if the COBall can no longer move.
hr = pInitData->m_pIBall->Move(TRUE);
bAlive = (NOERROR == hr);
// Set new timer end count.
nEndCount = GetTickCount() + pInitData->m_nDelay;
}
}
// UnInitialize COM for use by this thread.
CoUninitialize();
}
return 0;
}
Within each launched worker thread, COM is initialized specifying COINIT_MULTITHREADED to indicate the new thread will execute as part of the process's multi-threaded apartment. Each of the three threads executes this same re-entrant thread procedure. Within the procedure, each thread executes an indefinite while loop containing a call to the IBall::Move method on the COBall object. Because these move calls would be far too fast for human perception, each thread is kept busy in a delay countdown using the system timer tick count. This sample uses delays in the neighborhood of 100 milliseconds. When the delay is over, the Move method is called on the COBall object. The three threads are running concurrently and could make the Move calls at conflicting times. As explained in the FRESERVE sample, the Move method on COBall is guarded by the CThreaded OwnThis mechanism. If one of the threads currently owns the COBall object, a Move call by another thread will block the calling thread until it can obtain ownership.
Each thread's while loop terminates in BallThreadProc when the Move call that is made there returns E_FAIL. This return signals that some other thread had killed the ball by calling the Move method with the bAlive parameter set to FALSE. This terminating call is actually made by the main application thread and not by any of the ball-moving threads. The call is made in the CGuiBall destructor shown above. The destructor is run when the main CGuiBall object is deleted because the user has closed or exited the main application, causing an exit of the main process thread's message loop in WinMain.
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