Semaphore - Part 3

And lastly, the POSIX semaphore version. As I mentioned last post, I decided to use XSI-style semaphores, rather than the newer semaphores option. Since everything is supported by the OS, all we need to do is wrap the functions; this will be very straightforward. The class:

class CSemaphore // POSIX version of CSemaphore: XSI semaphore (slow) { private: int m_iSem; // Semaphore index inline int &GetSemaphore() { return m_iSem; } public: inline CSemaphore(long nInitialCount) { assert(nInitialCount >= 0); semun ctl; ctl.val = nCount; assert(ctl.val == nInitialCount); // Create the semaphore m_iSem = semget(IPC_PRIVATE, 1, S_IRUSR | S_IWUSR); if (m_iSem <= 0) throw bad_alloc("Unable to create semaphore"); // Initialize the semaphore count verify(semctl(m_iSem, 0, SETVAL, ctl) == 0); } inline ~CSemaphore() { verify(semctl(m_iSem, 0, IPC_RMID) == 0); } inline bool TryWait() { sembuf op; op.sem_num = 0; op.sem_op = -1; op.sem_flg = IPC_NOWAIT; // Don't wait if we can't lock it now return (semop(m_iSem, &op, 1) == 0); } inline void Wait() { sembuf op; op.sem_num = 0; op.sem_op = -1; op.sem_flg = 0; // Wait if necessary verify(semop(m_iSem, &op, 1) == 0); } inline void Post(long nCount = 1) { assert(nCount > 0); sembuf op; op.sem_num = 0; op.sem_op = nCount; op.sem_flg = 0; assert(op.sem_op == nCount); // Make sure there wasn't any truncation verify(semop(m_iSem, &op, 1) == 0); } };