semaphore.h File Reference

In-process counting semaphore with optional timeout. More...

#include <memory>
#include "./macros.h"

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Classes
class	vlink::Semaphore
	In-process counting semaphore with optional acquire timeout. More...

Namespaces
namespace	vlink

Detailed Description

In-process counting semaphore with optional timeout.

Semaphore provides classic P/V (acquire/release) semaphore semantics within a single process. It is built on std::mutex and std::condition_variable (via the VLink ConditionVariable, which uses CLOCK_MONOTONIC to avoid NTP clock-jump issues on Linux).

Typical use cases:

• Limiting concurrent access to a resource pool.
• Signalling between a producer and one or more consumers.
• Throttling task submission to a bounded work queue.

Note

• acquire() blocks the caller until at least n permits are available.
• release() is safe to call from any thread, including signal handlers (as long as the underlying std::mutex is signal-safe on the platform).
• reset() with interrupt_waiters == true is a disruptive operation that wakes all blocked acquire() callers and returns false to them. Use it only during controlled shutdown.
• This is an in-process semaphore. For cross-process synchronisation, use SysSemaphore.

Example

vlink::Semaphore sem(0);  // start at 0
 
// Producer:
do_work();
sem.release();  // signal one consumer
 
// Consumer:
if (sem.acquire(1, 100)) {  // wait up to 100 ms
  consume_result();
} else {
  handle_timeout();
}