Using Object Oriented Semaphore in C ++

Question

I know how to use Unix semaphores in C. Before using them, I have to call a constructor-ish function called sem_init , and after using them I need to call a destructor function called sem_destroy .

I know that I can continue to do this in C ++ because of its backward compatibility with C, but does C ++ have a real object-oriented way of using semaphores?

Answer 1

If you really insist on using POSIX semaphores rather than Boost, you can, of course, wrap sem_t in a class:

 class Semaphore { sem_t sem; public: Semaphore(int shared, unsigned value) { sem_init(&sem, shared, value); } ~Semaphore() { sem_destroy(&sem); } int wait() { return sem_wait(&sem); } int try_wait() { return sem_trywait(&sem); } int unlock() { return sem_post(&sem); } }; 

Exercise for the reader. You might want to add exceptions instead of C-style error codes and possibly other functions. In addition, this class must not be copyable. The easiest way to achieve this is to inherit from boost::noncopyable ;)

Edit : as @Ringding's remark, making a loop on an EINTR would be very reasonable.

 int Semaphore::wait() { int r; do { r = sem_wait(&sem); } while (r == -1 && errno == EINTR); return r; } 

Answer 2

You should use Boost libraries (if you don't know them, they are for C ++, which is the JDK for Java).

Boost.Interprocess is the library you need for your question. It provides an abstraction of interprocess communication mechanisms.

This is an example of using semaphores.

Answer 3

C ++ 0x doesn't have semaphores? How to synchronize streams?