sys_semaphore.h File Reference

Named, cross-process counting semaphore backed by the OS IPC layer. More...

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

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Classes
class	vlink::SysSemaphore
	Named cross-process counting semaphore. More...

Namespaces
namespace	vlink

Detailed Description

Named, cross-process counting semaphore backed by the OS IPC layer.

SysSemaphore wraps a named POSIX semaphore (on Linux/macOS) or a named Win32 semaphore to allow synchronisation between independent processes (or between processes and drivers) via a shared name in the OS namespace.

Lifecycle:

1. Construct the SysSemaphore object.
2. Call attach(name) to create or open a named semaphore.
3. Use acquire() / release() for P/V operations.
4. Call detach(force) to close the handle. If force is true the semaphore is also removed from the OS namespace.
5. The destructor calls detach() automatically.

Note

• The initial count passed to the constructor is only used when the semaphore is created by attach(). If the semaphore already exists in the OS namespace the constructor count is ignored and the existing value is used.
• Unlike Semaphore, this class may throw on attach() failures (e.g., permission denied, namespace exhausted).
• Semaphore names on POSIX must start with '/' (e.g., "/vlink_ready"). On Windows any non-empty string is accepted.

Example

// Process A (server) creates the semaphore:
vlink::SysSemaphore sem(0);
sem.attach("/vlink_ready");
do_init();
sem.release();  // signal Process B
 
// Process B (client) opens the same semaphore:
vlink::SysSemaphore sem;
sem.attach("/vlink_ready");
sem.acquire();  // blocks until Process A releases