Semaphore.md

Semaphore

Analogous to std::counting_semaphore, but it's for lazy.

Usage

Notifier

#include <async_simple/coro/Semaphore>

using namespace async_simple::coro;

BinarySemaphore notifier(0);
bool ready = false;

Lazy<> producer() {
  ready = true;
  co_await notifier.release();
  co_return;
}

Lazy<> consumer() {
  co_await notifier.acquire();
  assert(ready);
  co_return;
}

Mutex

#include <async_simple/coro/Semaphore>

using namespace async_simple::coro;

BinarySemaphore sem(1);
int count = 0;

Lazy<> producer() {
  co_await sem.acquire();
  ++count;
  co_await sem.release();
  co_return;
}

Lazy<> consumer() {
  co_await sem.acquire();
  --count;
  co_await sem.release();
  co_return;
}

Avoid memory leaking

When we co_await Semaphore::acquire() in a coroutine, we need to be sure that the semaphore will be released before the end of the execution of the program. Otherwise, the memomry will leak.