Programming with Windows* Threads Intel Software College

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 2 Programming with Windows Threads Objectives At the completion of this module you will be able to: Write code to create and terminate threads Use synchronization objects to coordinate thread execution and memory access

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 3 Programming with Windows Threads Agenda Explore Win32 Threading API functions Create threads Wait for threads to terminate Synchronize shared access between threads Labs to give hands-on experience

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 4 Programming with Windows Threads Windows* HANDLE type Each Windows object is referenced by HANDLE type variables Pointer to kernel objects Thread, process, file, event, mutex, semaphore, etc. Object creation functions return HANDLE Object controlled through its handle Don’t manipulate objects directly

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 5 Programming with Windows Threads Windows* Thread Creation HANDLE CreateThread( LPSECURITY_ATTRIBUTES ThreadAttributes, DWORD StackSize, LPTHREAD_START_ROUTINE StartAddress, LPVOID Parameter, DWORD CreationFlags, LPDWORD ThreadId ); // Out

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 6 Programming with Windows Threads LPTHREAD_START_ROUTINE CreateThread() expects pointer to global function Returns DWORD Calling convention WINAPI Single LPVOID (void *) parameter Thread begins execution of function DWORD WINAPI MyThreadStart(LPVOID p);

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 7 Programming with Windows Threads Using Explicit Threads Identify portions of code to thread Encapsulate code into function If code is already a function, a driver function may need to be written to coordinate work of multiple threads Add CreateThread call to assign thread(s) to execute function

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 8 Programming with Windows Threads Destroying Threads Frees OS resources Clean-up if done with thread before program completes Process exit does this for you BOOL CloseHandle(HANDLE hObject);

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 9 Programming with Windows Threads Example: Thread Creation #include DWORD WINAPI helloFunc(LPVOID arg ) { printf(“Hello Thread\n”); return 0; } main() { HANDLE hThread = CreateThread(NULL, 0, helloFunc, NULL, 0, NULL ); } What Happens?

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 10 Programming with Windows Threads Example Explained Main thread is process When process goes, all threads go Need some method of waiting for a thread to finish

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 11 Programming with Windows Threads #include BOOL threadDone = FALSE ; DWORD WINAPI helloFunc(LPVOID arg ) { printf(“Hello Thread\n”); threadDone = TRUE ; return 0; } main() { HANDLE hThread = CreateThread(NULL, 0, helloFunc, NULL, 0, NULL ); while (!threadDone); } Waiting for Windows* Thread Not a good idea! // wasted cycles!

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 12 Programming with Windows Threads Waiting for a Thread Wait for one object (thread) DWORD WaitForSingleObject( HANDLE hHandle, DWORD dwMilliseconds ); Calling thread waits (blocks) until Time expires Return code used to indicate this Thread exits (handle is signaled) Use INFINITE to wait until thread termination Does not use CPU cycles

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 13 Programming with Windows Threads Waiting for Many Threads Wait for up to 64 objects (threads) DWORD WaitForMultipleObjects( DWORD nCount, CONST HANDLE *lpHandles, // array BOOL fWaitAll, // wait for one or all DWORD dwMilliseconds) Wait for all: fWaitAll==TRUE Wait for any: fWaitAll==FALSE Return value is first array index found

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 14 Programming with Windows Threads Notes on WaitFor* Functions Handle as parameter Used for different types of objects Kernel objects have two states Signaled Non-signaled Behavior is defined by object referred to by handle Thread: signaled means terminated

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 15 Programming with Windows Threads Example: Multiple Threads #include const int numThreads = 4; DWORD WINAPI helloFunc(LPVOID arg ) { printf(“Hello Thread\n”); return 0; } main() { HANDLE hThread[numThreads]; for (int i = 0; i < numThreads; i++) hThread[i] = CreateThread(NULL, 0, helloFunc, NULL, 0, NULL ); WaitForMultipleObjects(numThreads, hThread, TRUE, INFINITE); }

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 16 Programming with Windows Threads Activity 1 - “HelloThreads” Modify the previous example code to print out Appropriate “Hello Thread” message Unique thread number Use for-loop variable of CreateThread loop Sample output: Hello from Thread #0 Hello from Thread #1 Hello from Thread #2 Hello from Thread #3

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 17 Programming with Windows Threads What’s wrong? What is printed for myNum? DWORD WINAPI threadFunc(LPVOID ) { DWORD WINAPI threadFunc(LPVOID pArg) { int* p = (int*)pArg; int* p = (int*)pArg; int myNum = *p; printf( “Thread number %d\n”, myNum);}... // from main(): for (int i = 0; i < numThreads; i++) { hThread[i] = hThread[i] = CreateThread(NULL, 0, threadFunc, &i, 0, NULL); CreateThread(NULL, 0, threadFunc, &i, 0, NULL);}

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 18 Programming with Windows Threads Hello Threads Timeline TimemainThread 0Thread 1 T0T0 i = T1T1 create(&i)--- T2T2 i++ (i == 1)launch--- T3T3 create(&i)p = pArg--- T4T4 i++ (i == 2)myNum = *p myNum = 2 launch T5T5 waitprint(2)p = pArg T6T6 waitexitmyNum = *p myNum = 2

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 19 Programming with Windows Threads Race Conditions Concurrent access of same variable by multiple threads Read/Write conflict Write/Write conflict Most common error in concurrent programs May not be apparent at all times

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 20 Programming with Windows Threads How to Avoid Data Races Scope variables to be local to threads Variables declared within threaded functions Allocate on thread’s stack TLS (Thread Local Storage) Control shared access with critical regions Mutual exclusion and synchronization Lock, semaphore, event, critical section, mutex…

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 21 Programming with Windows Threads Solution – “Local” Storage DWORD WINAPI threadFunc(LPVOID ) DWORD WINAPI threadFunc(LPVOID pArg){ (int*)pArg) int myNum = *((int*)pArg); printf( “Thread number %d\n”, myNum);}... // from main(): for (int i = 0; i < numThreads; i++) { tNum[i] = i; tNum[i] = i; hThread[i] = hThread[i] = CreateThread(NULL, 0, threadFunc, &tNum[i], CreateThread(NULL, 0, threadFunc, &tNum[i], 0, NULL); 0, NULL);}

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 22 Programming with Windows Threads Windows* Mutexes Kernel object reference by handle “Signaled” when available Operations: CreateMutex(…) // create new WaitForSingleObject // wait & lock ReleaseMutex(…) // unlock Available between processes

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 23 Programming with Windows Threads Windows* Critical Section Lightweight, intra-process only mutex Most useful and most used New type CRITICAL_SECTION cs; Create and destroy operations InitializeCriticalSection(&cs) DeleteCriticalSection(&cs);

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 24 Programming with Windows Threads Windows* Critical Section CRITICAL_SECTION cs ; Attempt to enter protected code EnterCriticalSection(&cs) Blocks if another thread is in critical section Returns when no thread is in critical section Upon exit of critical section LeaveCriticalSection(&cs) Must be from obtaining thread

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 25 Programming with Windows Threads Example: Critical Section #define NUMTHREADS 4 CRITICAL_SECTION g_cs; // why does this have to be global? int g_sum = 0; DWORD WINAPI threadFunc(LPVOID arg ) { int mySum = bigComputation(); EnterCriticalSection(&g_cs); g_sum += mySum; // threads access one at a time LeaveCriticalSection(&g_cs); return 0; } main() { HANDLE hThread[NUMTHREADS]; InitializeCriticalSection(&g_cs); for (int i = 0; i < NUMTHREADS; i++) hThread[i] = CreateThread(NULL,0,threadFunc,NULL,0,NULL); WaitForMultipleObjects(NUMTHREADS, hThread, TRUE, INFINITE); DeleteCriticalSection(&g_cs); }

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 26 Programming with Windows Threads Numerical Integration Example (1+x 2 ) f(x) =  4.0 (1+x 2 ) dx =  0 1 X static long num_steps=100000; double step, pi; void main() { int i; double x, sum = 0.0; step = 1.0/(double) num_steps; for (i=0; i< num_steps; i++){ x = (i+0.5)*step; sum = sum + 4.0/(1.0 + x*x); } pi = step * sum; printf(“Pi = %f\n”,pi); }

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 27 Programming with Windows Threads Activity 2 - Computing Pi Parallelize the numerical integration code using Windows* Threads How can the loop iterations be divided among the threads? What variables can be local? What variables need to be visible to all threads? static long num_steps=100000; double step, pi; void main() { int i; double x, sum = 0.0; step = 1.0/(double) num_steps; for (i=0; i< num_steps; i++){ x = (i+0.5)*step; sum = sum + 4.0/(1.0 + x*x); } pi = step * sum; printf(“Pi = %f\n”,pi);}

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 28 Programming with Windows Threads Windows* Semaphores Synchronization object that keeps a count Represents the number of available resources Formalized by Edsger Dijkstra (1968) Two operations on semaphores Wait [P(s)]: Thread waits until s > 0, then s = s-1 Post [V(s)]: s = s + 1 Semaphore is in signaled state if count > 0

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 29 Programming with Windows Threads Win32* Semaphore Creation HANDLE CreateSemaphore( LPSECURITY_ATTRIBUTES lpEventAttributes, LONG lSemInitial, // Initial count value LONG lSemMax, // Maximum value for count LPCSTR lpSemName); // text name for object Value of lSemMax must be 1 or greater Value of lSemInitial must be greater than or equal to zero, less than or equal to lSemMax, and cannot go outside of range

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 30 Programming with Windows Threads Wait and Post Operations Use WaitForSingleObject to wait on semaphore If count is == 0, thread waits Decrement count by 1 when count > 0 Increment semaphore (Post operation) BOOL ReleaseSemaphore( HANDLE hSemaphore, LONG cReleaseCount, LPLONG lpPreviousCount ); Increase semaphore count by cReleaseCount Returns the previous count through lpPreviousCount

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 31 Programming with Windows Threads Semaphore Uses Control access to data structures of limited size Queues, stacks, deques Use count to enumerate available elements Control access to finite number of resourse File descriptors, tape drives… Throttle number of active threads within a region Binary semaphore [0,1] can act as mutex

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 32 Programming with Windows Threads Semaphore Cautions No ownership of semaphore Any thread can release a semaphore, not just the last thread that waits Use good programming practice to avoid this No concept of abandoned semaphore If thread terminates before post, semaphore increment may be lost Deadlock

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 33 Programming with Windows Threads Example: Semaphore as Mutex Main thread opens input file, waits for thread termination Threads will Read line from input file Count all five-letter words in line

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 34 Programming with Windows Threads Example: Main main() { HANDLE hThread[NUMTHREADS]; hSem1 = CreateSemaphore(NULL, 1, 1, NULL); // Binary semaphore hSem2 = CreateSemaphore(NULL, 1, 1, NULL); // Binary semaphore fd = fopen(“InFile”, “r”); // Open file for read for (int i = 0; i < NUMTHREADS; i++) hThread[i] = CreateThread(NULL,0,CountFives,NULL,0,NULL); WaitForMultipleObjects(NUMTHREADS, hThread, TRUE, INFINITE); fclose(fd); printf(“Number of five letter words is %d\n”, fiveLetterCount); } HANDLE hSem1, hSem2; FILE *fd; int fiveLetterCount = 0;

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 35 Programming with Windows Threads Example: Semaphores DWORD WINAPI CountFives(LPVOID arg) { BOOL bDone = FALSE ; char inLine[132]; int lCount = 0; while (!bDone) { WaitForSingleObject(hSem1, INFINITE); // access to input bDone = (GetNextLine(fd, inLine) == EOF); ReleaseSemaphore(hSem1, 1, NULL); if (!bDone) if (lCount = GetFiveLetterWordCount(inLine)) { WaitForSingleObject(hSem2, INFINITE); // update global fiveLetterCount += lCount; ReleaseSemaphore(hsem2, 1, NULL); }

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 36 Programming with Windows Threads Activity 3 – Using Semaphores Use binary semaphores to control access to shared variables

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 37 Programming with Windows Threads Windows* Events Used to signal other threads that some event has occurred Data is available, message is ready Threads wait for signal with WaitFor * function Two kinds of events Auto-reset Manual-reset

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 38 Programming with Windows Threads Types of Events Event stays signaled until any one thread waits and is released If no threads waiting, state stays signaled Once thread is released, state reset to non-signaled Event remains signaled until reset by API call Multiple threads can wait and be released Threads not originally waiting may start wait and be released Caution: Be careful when using WaitForMultipleObjects to wait for ALL events Manual-resetAuto-reset

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 39 Programming with Windows Threads Windows* Event Creation HANDLE CreateEvent( LPSECURITY_ATTRIBUTES lpEventAttributes, BOOL bManualReset, // TRUE => manual reset BOOL bInitialState, // TRUE => begin signaled LPCSTR lpName); // text name for object Set bManualReset to TRUE for manual-reset event; FALSE for auto-reset event Set bInitialState to TRUE for event to begin in signaled state; FALSE to begin unsignaled

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 40 Programming with Windows Threads Event Set and Reset Set an event to signaled state BOOL SetEvent( HANDLE event ); Reset manual-reset event BOOL ResetEvent( HANDLE event ); Pulse event BOOL PulseEvent( HANDLE event );

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 41 Programming with Windows Threads Example: Thread Search Created thread searches for item Signals if item is found Main thread waits for signal and thread termination Print message if item found Print message upon thread termination Illustrates Using generic HANDLE type Not waiting for every object to signal

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 42 Programming with Windows Threads Example: Events DWORD WINAPI threadFunc(LPVOID arg) { BOOL bFound = bigFind() ; if (bFound) { SetEvent(hObj[0]); // signal data was found bigFound() ; } moreBigStuff() ; return 0; } HANDLE hObj[2]; // 0 is event, 1 is thread

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 43 Programming with Windows Threads Example: Main function... hObj[0] = CreateEvent(NULL, FALSE, FALSE, NULL); hObj[1] = CreateThread(NULL,0,threadFunc,NULL,0,NULL); /* Do some other work while thread executes search */ DWORD waitRet = WaitForMultipleObjects(2, hObj, FALSE, INFINITE); switch(waitRet) { case WAIT_OBJECT_0: // event signaled printf("found it!\n"); WaitForSingleObject(hObj[1], INFINITE) ; // fall thru case WAIT_OBJECT_0+1:// thread signaled printf("thread done\n"); break ; default: printf("wait error: ret %u\n", waitRet); break ; }...

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 44 Programming with Windows Threads Example: Main function... hObj[0] = CreateEvent(NULL, FALSE, FALSE, NULL); hObj[1] = CreateThread(NULL,0,threadFunc,NULL,0,NULL); /* Do some other work while thread executes search */ DWORD waitRet = WaitForMultipleObjects(2, hObj, FALSE, INFINITE); switch(waitRet) { case WAIT_OBJECT_0: // event signaled printf("found it!\n"); WaitForSingleObject(hObj[1], INFINITE) ; // fall thru case WAIT_OBJECT_0+1:// thread signaled printf("thread done\n"); break ; default: printf("wait error: ret %u\n", waitRet); break ; }...

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 45 Programming with Windows Threads Activity 4 – Using Events Replace spin-wait and thread counting variable with events to signal thread completion of computational piece

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 46 Programming with Windows Threads Programming with Windows Threads What’s Been Covered Create threads to execute work encapsulated within functions Typical to wait for threads to terminate Coordinate shared access between threads to avoid race conditions Local storage to avoid conflicts Synchronization objects to organize use

Copyright © 2006, Intel Corporation. All rights reserved. Intel and the Intel logo are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States or other countries. *Other brands and names are the property of their respective owners. 47 Programming with Windows Threads