mirror of
https://github.com/golang/go
synced 2024-11-20 09:24:50 -07:00
5bbd4c2f1b
more enforcing package boundaries R=r DELTA=46 (13 added, 15 deleted, 18 changed) OCL=35806 CL=35806
115 lines
3.2 KiB
Go
115 lines
3.2 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// The sync package provides basic synchronization primitives
|
|
// such as mutual exclusion locks. These are intended for use
|
|
// by low-level library routines. Higher-level synchronization
|
|
// is better done via channels and communication.
|
|
package sync
|
|
|
|
import "runtime"
|
|
|
|
func cas(val *uint32, old, new uint32) bool
|
|
|
|
// A Mutex is a mutual exclusion lock.
|
|
// Mutexes can be created as part of other structures;
|
|
// the zero value for a Mutex is an unlocked mutex.
|
|
type Mutex struct {
|
|
key uint32;
|
|
sema uint32;
|
|
}
|
|
|
|
func xadd(val *uint32, delta int32) (new uint32) {
|
|
for {
|
|
v := *val;
|
|
nv := v+uint32(delta);
|
|
if cas(val, v, nv) {
|
|
return nv;
|
|
}
|
|
}
|
|
panic("unreached");
|
|
}
|
|
|
|
// Lock locks m.
|
|
// If the lock is already in use, the calling goroutine
|
|
// blocks until the mutex is available.
|
|
func (m *Mutex) Lock() {
|
|
if xadd(&m.key, 1) == 1 {
|
|
// changed from 0 to 1; we hold lock
|
|
return;
|
|
}
|
|
runtime.Semacquire(&m.sema);
|
|
}
|
|
|
|
// Unlock unlocks m.
|
|
// It is a run-time error if m is not locked on entry to Unlock.
|
|
//
|
|
// A locked Mutex is not associated with a particular goroutine.
|
|
// It is allowed for one goroutine to lock a Mutex and then
|
|
// arrange for another goroutine to unlock it.
|
|
func (m *Mutex) Unlock() {
|
|
if xadd(&m.key, -1) == 0 {
|
|
// changed from 1 to 0; no contention
|
|
return;
|
|
}
|
|
runtime.Semrelease(&m.sema);
|
|
}
|
|
|
|
// Stub implementation of r/w locks.
|
|
// This satisfies the semantics but
|
|
// is not terribly efficient.
|
|
|
|
// The next comment goes in the BUGS section of the document,
|
|
// in its own paragraph, without the (rsc) tag.
|
|
|
|
// BUG(rsc): RWMutex does not (yet) allow multiple readers;
|
|
// instead it behaves as if RLock and RUnlock were Lock and Unlock.
|
|
|
|
// An RWMutex is a reader/writer mutual exclusion lock.
|
|
// The lock can be held by an arbitrary number of readers
|
|
// or a single writer.
|
|
// RWMutexes can be created as part of other
|
|
// structures; the zero value for a RWMutex is
|
|
// an unlocked mutex.
|
|
type RWMutex struct {
|
|
m Mutex;
|
|
}
|
|
|
|
// RLock locks rw for reading.
|
|
// If the lock is already locked for writing or there is a writer already waiting
|
|
// to acquire the lock, RLock blocks until the writer has released the lock.
|
|
func (rw *RWMutex) RLock() {
|
|
rw.m.Lock();
|
|
}
|
|
|
|
// RUnlock undoes a single RLock call;
|
|
// it does not affect other simultaneous readers.
|
|
// It is a run-time error if rw is not locked for reading
|
|
// on entry to RUnlock.
|
|
func (rw *RWMutex) RUnlock() {
|
|
rw.m.Unlock();
|
|
}
|
|
|
|
// Lock locks rw for writing.
|
|
// If the lock is already locked for reading or writing,
|
|
// Lock blocks until the lock is available.
|
|
// To ensure that the lock eventually becomes available,
|
|
// a blocked Lock call excludes new readers from acquiring
|
|
// the lock.
|
|
func (rw *RWMutex) Lock() {
|
|
rw.m.Lock();
|
|
}
|
|
|
|
// Unlock unlocks rw for writing.
|
|
// It is a run-time error if rw is not locked for writing
|
|
// on entry to Unlock.
|
|
//
|
|
// Like for Mutexes,
|
|
// a locked RWMutex is not associated with a particular goroutine.
|
|
// It is allowed for one goroutine to RLock (Lock) an RWMutex and then
|
|
// arrange for another goroutine to RUnlock (Unlock) it.
|
|
func (rw *RWMutex) Unlock() {
|
|
rw.m.Unlock();
|
|
}
|