Multithread API’s

1. Multithread API’s Adam Piotrowski Grzegorz Jabłoński Lecture IV

2. Synchronisation Mutexes Semaphores Condition Variables

3. Mutex The mutual exclusion lock is the simplest and mostprimitive synchronizationvariable. It provides a single, absolute owner for the section of code (thus acritical section) that it brackets between the calls to pthread_mutex_lock() and pthread_mutex_unlock(). The first thread that locks the mutex getsownership, and any subsequent attempts to lock it will fail, causing the callingthread to go to sleep.

4. Mutex initialisation NAME pthread_mutex_init, pthread_mutex_destroy- initializes mutex with attr or destroys the mutex, making it unusable in any form SYNOPSIS #include <pthread.h> int pthread_mutex_init(pthread_mutex_t *mutex, constpthread_mutexattr_t *attr); int pthread_mutex_destroy(pthread_mutex_t *mutex);

5. Mutex unlock operation NAME pthread_mutex_unlock- unlocks mutex and wakes up the first thread sleeping on it. SYNOPSIS #include <pthread.h> int pthread_mutex_unlock(pthread_mutex_t *mutex);

6. Mutex example thread 1 thread 2 request_t *remove() { pthread_mutex_lock(&lock); ...sleeping... request = requests; requests = requests->next; pthread_mutex_unlock(&lock) return(request); } add(request_t *request) { pthread_mutex_lock(&lock); request->next = requests; requests = request pthread_mutex_unlock(&lock); }

7. Mutex example

8. Semaphores A counting semaphore6 is a variable that youcan increment arbitrarily high, but decrement only to zero. A sem_post()operation increments the semaphore, while asem_wait() attempts to decrement it. If thesemaphore is greater than zero, the operation succeeds; if not, then the callingthread must go to sleep until a different thread increments it.

9. Semaphores initialisation NAME sem_init, sem_destroy- initializes the semaphore to value. If pshared is non-zero,then the semaphore will be sharable among processes.This destroys the semaphore. SYNOPSIS #include <pthread.h> int sem_init(sem_t *sem, int pshared, unsigned int value);int sem_destroy(sem_t *sem);

10. Semaphores operations NAME sem_post,sem_wait, sem_trywait- function increments the value of the semaphore or decrements the value of sem by one. If the semaphore’s value is zero,sem_wait() blocks, waiting for the semaphore to be incremented byanother process or thread, while sem_trywait() will returnimmediately. SYNOPSIS #include <pthread.h> int sem_post(sem_t *sem); int sem_trywait(sem_t *sem); int sem_wait(sem_t *sem);

11. Semaphores operations

12. Semaphores operations NAME sem_open,sem_close- returns a pointer to the semaphore name. All processes which callthis on the same name will get the same semaphore pointer or closes the named semaphore for this process. SYNOPSIS #include <pthread.h> sem_t *sem_open(char *name, int oflag,... ); int sem_close(sem_t *sem);

13. Semaphors example

14. Semaphors example request_t *get_request() {request_t *request; request = (request_t *) malloc(sizeof(request_t)); request->data = read_from_net(); return(request) } void process_request(request_t *request) { process(request->data); free(request); } producer() {request_t *request; while(1){ request = get_request(); add(request); sem_post(&requests_length); } } consumer() {request_t *request; while(1){SEM_WAIT(&requests_length); request = remove(); process_request(request); } }

15. Conditional Variables

16. Conditional Variable initialisation NAME pthread_cond_init, pthread_cond_destroy- initializes cond with att or destroys the condition variable, making it unusable in any form. SYNOPSIS #include <pthread.h> int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr); int pthread_cond_destroy(pthread_cond_t *cond);

17. Conditional Variable Wait Operation NAME pthread_cond_wait, pthread_cond_timewait- atomically releases mutex and causes the calling thread to block oncond. Upon successful return, the mutex will be reacquired. SYNOPSIS #include <pthread.h> int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec*abstime);

18. Conditional Variable Signal Operation NAME pthread_cond_signal,pthread_cond_broadcast- unblocks the first thread (if any) blocked on a condition variable or unblocks all threads blocked on a condition variable. You do not know the order in which they awake. SYNOPSIS #include <pthread.h> int pthread_cond_signal(pthread_cond_t *cond);int pthread_cond_broadcast(pthread_cond_t *cond);

19. Conditional Variable Example thread 1 thread 2 pthread_mutex_lock(&m); my_condition = TRUE; pthread_mutex_unlock(&m); pthread_cond_signal(&c); pthread_mutex_lock(&m); while (!my_condition) pthread_cond_wait(&c, &m); ... sleeping ... do_thing() pthread_mutex_unlock(&m);

20. Conditional Variable Example

21. Conditional Variable Example void *producer(void *arg) {request_t *request; while(1) { request = get_request(); pthread_mutex_lock(&r_lock); while (length >= 10) pthread_cond_wait(&r_producer, &r_lock); add(request); length++;pthread_mutex_unlock(&r_lock); pthread_cond_signal(&r_consumer); } } void *consumer(void *arg) {request_t *request; while(1) {pthread_mutex_lock(&r_lock); while (length == 0) pthread_cond_wait(&r_consumer, &r_lock); request = remove(); length--; pthread_mutex_unlock(&r_lock); pthread_cond_signal(&r_producer); process_request(request); } }

22. Multithread API’sWindows OS

23. Processes NAME CreateProcess - creates a new process and its primary thread. SYNOPSIS BOOL CreateProcess(LPCTSTRlpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORDdwCreationFlags, LPVOIDlpEnvironment, LPCTSTRlpCurrentDirectory, LPSTARTUPINFOlpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

24. Processes Pointer to a null-terminated string that specifies the module to execute. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTRlpApplicationName, LPTSTR lpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOL bInheritHandles, DWORD dwCreationFlags, LPVOID lpEnvironment, LPCTSTR lpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

25. Processes Pointer to a null-terminated string that specifies the command line to execute. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOL bInheritHandles, DWORD dwCreationFlags, LPVOID lpEnvironment, LPCTSTR lpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

26. Processes A pointer to a SECURITY_ATTRIBUTES structure that determines whether the returned handle can be inherited by child processes. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOL bInheritHandles, DWORD dwCreationFlags, LPVOID lpEnvironment, LPCTSTR lpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

27. Processes If this parameter TRUE, each inheritable handle in the calling process is inherited by the new process. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORD dwCreationFlags, LPVOID lpEnvironment, LPCTSTR lpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

28. Processes Additionalcreationflagse.g. CREATE_NEW_CONSOLE, CREATE_SUSPENDED, DETACHED_PROCESS NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORDdwCreationFlags, LPVOID lpEnvironment, LPCTSTR lpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

29. Processes A pointer to the environment block for the new process. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORDdwCreationFlags, LPVOIDlpEnvironment, LPCTSTR lpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

30. Processes The full path to the current directory for the process. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORDdwCreationFlags, LPVOIDlpEnvironment, LPCTSTRlpCurrentDirectory, LPSTARTUPINFO lpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

31. Processes A pointer to a STARTUPINFO NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORDdwCreationFlags, LPVOIDlpEnvironment, LPCTSTRlpCurrentDirectory, LPSTARTUPINFOlpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

32. Processes A pointer to a PROCESS_INFORMATION structure that receives identification information about the new process. NAME CreateProcess- creates a new process and its primary thread. SYNOPSIS BOOLCreateProcess( LPCTSTR lpApplicationName, LPTSTRlpCommandLine, LPSECURITY_ATTRIBUTESlpProcessAttributes, LPSECURITY_ATTRIBUTESlpThreadAttributes, BOOLbInheritHandles, DWORDdwCreationFlags, LPVOIDlpEnvironment, LPCTSTRlpCurrentDirectory, LPSTARTUPINFOlpStartupInfo, LPPROCESS_INFORMATIONlpProcessInformation );

33. Process example void _tmain( int argc, TCHAR *argv[] ) { STARTUPINFO si; PROCESS_INFORMATION pi; if( !CreateProcess( NULL, // No module name (use command line) argv[1], // Command line NULL, // Process handle not inheritable NULL, // Thread handle not inheritable FALSE, // Set handle inheritance to FALSE 0, // No creation flags NULL, // Use parent's environment block NULL, // Use parent's starting directory &si, // Pointer to STARTUPINFO structure &pi ) // Pointer to PROCESS_INFORMATION structure ) { printf( "CreateProcess failed (%d)\n", GetLastError() ); return; } // Wait until child process exits. WaitForSingleObject( pi.hProcess, INFINITE ); // Close process and thread handles. CloseHandle( pi.hProcess ); CloseHandle( pi.hThread ); }

34. Threads NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLE CreateThread( LPSECURITY_ATTRIBUTES lpsa, DWORD cbStack, LPTHREAD_START_ROUTINE lpStartAddr, LPVOID lpvThreadParam, DWORD fdwCreate, LPDWORD lpIDThread );

35. Threads A pointer to a SECURITY_ATTRIBUTES structure that determines whether the returned handle can be inherited by child processes. NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLECreateThread( LPSECURITY_ATTRIBUTESlpsa, DWORDcbStack, LPTHREAD_START_ROUTINElpStartAddr, LPVOIDlpvThreadParam, DWORDfdwCreate, LPDWORDlpIDThread );

36. Threads The initial size of the stack, in bytes. NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLECreateThread( LPSECURITY_ATTRIBUTESlpsa, DWORDcbStack, LPTHREAD_START_ROUTINElpStartAddr, LPVOIDlpvThreadParam, DWORDfdwCreate, LPDWORDlpIDThread );

37. Threads A pointer to the application-defined function to be executed by the thread and represents the starting address of the thread. DWORDThreadProc(LPVOIDlpParameter ); NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLECreateThread( LPSECURITY_ATTRIBUTESlpsa, DWORD cbStack, LPTHREAD_START_ROUTINElpStartAddr, LPVOIDlpvThreadParam, DWORDfdwCreate, LPDWORDlpIDThread );

38. Threads A pointer to a variable to be passed to the thread. NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLECreateThread( LPSECURITY_ATTRIBUTESlpsa, DWORD cbStack, LPTHREAD_START_ROUTINE lpStartAddr, LPVOIDlpvThreadParam, DWORDfdwCreate, LPDWORDlpIDThread );

39. Threads The flags that control the creation of the threadi.e.CREATE_SUSPENDED. NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLECreateThread( LPSECURITY_ATTRIBUTESlpsa, DWORD cbStack, LPTHREAD_START_ROUTINE lpStartAddr, LPVOID lpvThreadParam, DWORDfdwCreate, LPDWORDlpIDThread );

40. Threads A pointer to a variable that receives the thread identifier. NAME CreateThread- creates a thread to execute within the address space of the calling process. SYNOPSIS HANDLECreateThread( LPSECURITY_ATTRIBUTESlpsa, DWORD cbStack, LPTHREAD_START_ROUTINE lpStartAddr, LPVOID lpvThreadParam, DWORD fdwCreate, LPDWORDlpIDThread );

41. Threads - Example int _tmain() { PMYDATApData[MAX_THREADS]; DWORDdwThreadId[MAX_THREADS]; HANDLEhThread[MAX_THREADS]; inti; for( i=0; i<MAX_THREADS; i++ ) { pData[i] = (PMYDATA) HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(MYDATA)); pData->val1 = i; pData->val2 = i+100; hThread[i] = CreateThread( NULL, // default security attributes 0, // use default stack size MyThread, // thread function pData, // argument to thread function 0, // use default creation flags &dwThreadId[i]); // returns the thread identifier }} WaitForMultipleObjects(MAX_THREADS, hThread, TRUE, INFINITE); // Close all thread handles and free memory allocation. for(i=0; i<MAX_THREADS; i++) { CloseHandle(hThread[i]); } HeapFree(GetProcessHeap(), 0, pData[i]); return 0; }

42. What is wrong with CreateThread function ? A thread in an executable that calls the C run-time library (CRT) should use the _beginthreadex and _endthreadex functions for thread management rather than CreateThread and ExitThread

43. _beginthreadex NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsigned stack_size, unsigned ( *start_address )( void * ), void *arglist, unsigned initflag, unsigned *thrdaddr );

44. _beginthreadex Pointer to a SECURITY_ATTRIBUTES structure that determines whether the returned handle can be inherited by child processes. NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsignedstack_size, unsigned ( *start_address )( void * ), void *arglist, unsignedinitflag, unsigned *thrdaddr );

45. _beginthreadex Stack size for a new thread or 0. NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsignedstack_size, unsigned ( *start_address )( void * ), void *arglist, unsignedinitflag, unsigned *thrdaddr );

46. _beginthreadex Start address of a routine that begins execution of a new thread. NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsignedstack_size, unsigned( *start_address )(void* ), void *arglist, unsignedinitflag, unsigned *thrdaddr );

47. _beginthreadex Argument list to be passed to a new thread. NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsignedstack_size, unsigned ( *start_address )( void * ), void*arglist, unsignedinitflag, unsigned *thrdaddr );

48. _beginthreadex Argument list to be passed to a new thread. NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsignedstack_size, unsigned ( *start_address )( void * ), void *arglist, unsignedinitflag, unsigned *thrdaddr );

49. _beginthreadex Points to a 32-bit variable that receives the thread identifierlist to be passed to a new thread. NAME _beginthreadex - creates a thread to execute within the address space of the calling process. SYNOPSIS uintptr_t _beginthreadex( void *security, unsignedstack_size, unsigned ( *start_address )( void * ), void *arglist, unsigned initflag, unsigned*thrdaddr );

50. _beginthreadex example int main() { HANDLEhThread; unsignedthreadID; printf( "Creating second thread...\n" ); hThread = (HANDLE)_beginthreadex( NULL, 0, &SecondThreadFunc, NULL, 0, &threadID ); WaitForSingleObject( hThread, INFINITE ); CloseHandle( hThread ); }