Mutex.md

Mutex

Mutual exclusion module. Provides procedures for creating and operating on mutex locks for thread synchronization. Requires --m2plus and links with pthreads.

Exported Types

TYPE Mutex;  (* opaque mutex handle *)

Exported Procedures

PROCEDURE Create(): Mutex;
PROCEDURE Lock(m: Mutex);
PROCEDURE Unlock(m: Mutex);
PROCEDURE Destroy(m: Mutex);

Notes

• Create allocates and initializes a new mutex.
• Lock acquires the mutex, blocking if it is already held.
• Unlock releases the mutex.
• Destroy frees the mutex resources.
• Prefer the LOCK statement over manual Lock/Unlock calls, as LOCK guarantees the mutex is released even on exceptions.

Example

MODULE MutexDemo;
FROM Mutex IMPORT Mutex, Create, Lock, Unlock, Destroy;

VAR
  mu: Mutex;
  shared: INTEGER;

PROCEDURE SafeIncrement;
BEGIN
  Lock(mu);
  shared := shared + 1;
  Unlock(mu);
END SafeIncrement;

BEGIN
  mu := Create();
  shared := 0;
  SafeIncrement();
  Destroy(mu);
END MutexDemo.