Semaphore

class Semaphore

A classic semaphore synchronization primitive.

A semaphore manages an internal counter which is decremented by each acquire() call and incremented by each release() call. The counter can never go below zero; when acquire() finds that it is zero, it blocks, waiting until some other thread calls release().

Inheritance diagram

explicit Semaphore(int initial_count = 1)

void acquire(void)

Decrements the internal count. If the count was already at zero, blocks until the count is nonzero, then decrements it.

int get_count(void) const

Returns the current semaphore count. Note that this call is not thread- safe (the count may change at any time).

void output(std::ostream &out) const

int release(void)

Increments the semaphore’s internal count. This may wake up another thread blocked on acquire().

Returns the count of the semaphore upon release.

bool try_acquire(void)

If the semaphore can be acquired without blocking, does so and returns true. Otherwise, returns false.