CreateThreads and Synchronization in Win32: DLLs, Critical Sections, Mutexes, and Events, Slides of Windows Programming

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LL e c te c t u ru r ee

Review of Last Lecture

• DLLs and threads
• _beginthread()
• _endthread()
• CreateThread()
• Thread procedure: THREADPROC
• ExitThread()
• Supend/ResumeThread(), Sleep()
• Thread object and thread handles

CreateThread()

enum Shape { RECTANGLE, ELLIPSE };

DWORD WINAPI drawThread(LPVOID shape);

SYSTEMTIME st;

HANDLE CreateThread(

LPSECURITY_ATTRIBUTES lpThreadAttributes, // SD DWORD dwStackSize, // initial stack size LPTHREAD_START_ROUTINE lpStartAddress, // thread function LPVOID lpParameter, // thread argument DWORD dwCreationFlags, // creation option LPDWORD lpThreadId // thread identifier

);

Threads example

hThread1 = CreateThread(NULL, 0, drawThread, (LPVOID)RECTANGLE, CREATE_SUSPENDED, &dwThread1); hThread2 = CreateThread(NULL, 0, drawThread, (LPVOID)ELLIPSE, CREATE_SUSPENDED, &dwThread2);

hDC = GetDC(hWnd);

hBrushRectangle=CreateSolidBrush(RGB(170,220,160));

hBrushEllipse = CreateHatchBrush(HS_BDIAGONAL,RGB(175,180,225));

InitializeCriticalSection(&cs);

srand( (unsigned)time(NULL) ); ResumeThread(hThread2); ResumeThread(hThread1);

Threads Synchronization

• The problem: GDI handle is shared among

threads. Only one thread must draw using this

handle, at one time

• SYSTEMTIME
• The solution: Critical Section Kernel Object

Critical Section Object

• CRITICAL_SECTION object
• InitializeCriticalSection
• EnterCriticalSection
• LeaveCriticalSection
• DeleteCriticalSection

The Mutex Object

• Description

HANDLE CreateMutex(

LPSECURITY_ATTRIBUTES lpMutexAttributes, // SD

BOOL bInitialOwner, // initial owner

LPCTSTR lpName // object name

);

DWORD WaitForSingleObject(

HANDLE hHandle, // handle to object

DWORD dwMilliseconds // time-out interval

INFINITE, WAIT_TIMEOUT, WAIT_OBJECT_

The Mutex Object

BOOL ReleaseMutex(

HANDLE hMutex // handle to mutex

When the Mutex object is no longer needed, call

CloseHandle( handle );

Threads example with Mutex

hThread1 = CreateThread(NULL, 0, drawThread,

(LPVOID)RECTANGLE, CREATE_SUSPENDED,

&dwThread1);

hThread2 = .. .. ..

hBrushRectangle =

CreateSolidBrush(RGB(170,220,160));

hBrushEllipse=CreateHatchBrush(HS_BDIAGONAL,

RGB(175,180,225));

hMutex=CreateMutex(NULL, 0, NULL);

srand( (unsigned)time(NULL) );

ResumeThread(hThread2);

Threads example

for(i=0; i<10000; ++i)

Switch(WaitForSingleObject(hMutex,

INFINITE))

case WAIT_OBJECT_0:

SelectObject(hDC, hBrushRectangle);

Rectangle(hDC, 50, 1, rand()%300,

rand()%100);

GetLocalTime(&st);

ReleaseMutex(hMutex);

Sleep(10);

Multiple instance of the same application

• Create a Named Mutex with some unique

name using CreateMutex()

• If there is error creating Mutex object, call

GetLastError()

• If GetLastError() returns

ERROR_ALREADY_EXISTS, another instance of

the same application is already running

Event Object

Description:

• CreateEvent()
• Manual Reset and Auto-reset events
• SetEvent(), ResetEvent()
• PulseEvent()

Waiting for Multiple Objects

DWORD WaitForMultipleObjects(

DWORD nCount, // number of handles in array

CONST HANDLE *lpHandles, // object-handle array

BOOL fWaitAll, // wait option

DWORD dwMilliseconds // time-out interval

);

Returns:

WAIT_OBJECT_0 to (WAIT_OBJECT_0 + nCount – 1)

Semaphore Object

• Description: Limiting the maximum number of

threads in a system. Utilisation of a resource

HANDLE CreateSemaphore(

LPSECURITY_ATTRIBUTES lpSemaphoreAttributes, // SD

LONG lInitialCount, // initial count

LONG lMaximumCount, // maximum count

LPCTSTR lpName // object name

);