Skip to content

Threads.md

Latest commit

 

History

History
74 lines (51 loc) · 1.79 KB

Threads.md

File metadata and controls

74 lines (51 loc) · 1.79 KB

Threads

Why

Provides mutex, condition variable, and thread spawning primitives via a thin pthreads wrapper. All operations delegate to a C shim so the Modula-2 side stays minimal. Requires -lpthread at link time.

Types

  • Mutex (ADDRESS) -- Opaque mutex handle.
  • Cond (ADDRESS) -- Opaque condition variable handle.
  • ThreadProc -- PROCEDURE(ADDRESS) -- Entry point for a spawned thread.

Procedures

Mutex

  • PROCEDURE MutexInit(VAR m: Mutex) Allocate and initialise a mutex.

  • PROCEDURE MutexDestroy(VAR m: Mutex) Destroy a mutex and free its resources.

  • PROCEDURE MutexLock(m: Mutex) Acquire the mutex. Blocks until available.

  • PROCEDURE MutexUnlock(m: Mutex) Release the mutex.

Condition Variable

  • PROCEDURE CondInit(VAR c: Cond) Allocate and initialise a condition variable.

  • PROCEDURE CondDestroy(VAR c: Cond) Destroy a condition variable and free its resources.

  • PROCEDURE CondWait(c: Cond; m: Mutex) Atomically release the mutex and wait on the condition. Re-acquires the mutex on wake.

  • PROCEDURE CondSignal(c: Cond) Wake one thread waiting on the condition.

  • PROCEDURE CondBroadcast(c: Cond) Wake all threads waiting on the condition.

Thread

  • PROCEDURE SpawnThread(proc: ThreadProc; arg: ADDRESS) Create and start a new thread running proc(arg). The thread is detached.

Example

MODULE ThreadDemo;

FROM SYSTEM IMPORT ADDRESS;
FROM Threads IMPORT Mutex, MutexInit, MutexLock, MutexUnlock,
                     SpawnThread, ThreadProc;
FROM InOut IMPORT WriteString, WriteLn;

VAR
  mtx: Mutex;

  PROCEDURE Worker(arg: ADDRESS);
  BEGIN
    MutexLock(mtx);
    WriteString("hello from thread"); WriteLn;
    MutexUnlock(mtx)
  END Worker;

BEGIN
  MutexInit(mtx);
  SpawnThread(Worker, NIL);
END ThreadDemo.