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Copy pathgmutex.go
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227 lines (208 loc) · 5.88 KB
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// Copyright 2019 gf Author(https://github.com/gogf/gf). All Rights Reserved.
//
// This Source Code Form is subject to the terms of the MIT License.
// If a copy of the MIT was not distributed with this file,
// You can obtain one at https://github.com/gogf/gf.
// Package gmutex implements graceful concurrent-safe mutex with more rich features.
package gmutex
import (
"math"
"runtime"
"github.com/gogf/gf/container/gtype"
)
// The high level Mutex, which implements more rich features for mutex.
type Mutex struct {
state *gtype.Int32 // Indicates the state of mutex.
writer *gtype.Int32 // Pending writer count.
reader *gtype.Int32 // Pending reader count.
writing chan struct{} // Channel for writer blocking.
reading chan struct{} // Channel for reader blocking.
}
// New creates and returns a new mutex.
func New() *Mutex {
return &Mutex{
state: gtype.NewInt32(),
writer: gtype.NewInt32(),
reader: gtype.NewInt32(),
writing: make(chan struct{}, 1),
reading: make(chan struct{}, math.MaxInt32),
}
}
// Lock locks the mutex for writing purpose.
// If the mutex is already locked by another goroutine for reading or writing,
// it blocks until the lock is available.
func (m *Mutex) Lock() {
for {
// Using CAS operation to get the writing lock atomically.
if m.state.Cas(0, -1) {
return
}
// It or else blocks to wait for the next chance.
m.writer.Add(1)
<-m.writing
}
}
// Unlock unlocks writing lock on the mutex.
// It is safe to be called multiple times even there's no locks.
func (m *Mutex) Unlock() {
if m.state.Cas(-1, 0) {
// Note that there might be more than one goroutines can enter this block.
var n int32
// Writing lock unlocks, then first check the blocked readers.
// If there're readers blocked, it unlocks them with preemption.
for {
if n = m.reader.Val(); n > 0 {
if m.reader.Cas(n, 0) {
for ; n > 0; n-- {
m.reading <- struct{}{}
}
break
} else {
runtime.Gosched()
}
} else {
break
}
}
// It then also kindly feeds the pending writers with one chance.
if n = m.writer.Val(); n > 0 {
if m.writer.Cas(n, n-1) {
m.writing <- struct{}{}
}
}
}
}
// TryLock tries locking the mutex for writing purpose.
// It returns true immediately if success, or if there's a write/reading lock on the mutex,
// it returns false immediately.
func (m *Mutex) TryLock() bool {
if m.state.Cas(0, -1) {
return true
}
return false
}
// RLock locks mutex for reading purpose.
// If the mutex is already locked for writing,
// it blocks until the lock is available.
func (m *Mutex) RLock() {
var n int32
for {
if n = m.state.Val(); n >= 0 {
// If there's no writing lock currently, then do the reading lock checks.
if m.state.Cas(n, n+1) {
return
} else {
runtime.Gosched()
}
} else {
// It or else pends the reader.
m.reader.Add(1)
<-m.reading
}
}
}
// RUnlock unlocks the reading lock on the mutex.
// It is safe to be called multiple times even there's no locks.
func (m *Mutex) RUnlock() {
var n int32
for {
if n = m.state.Val(); n >= 1 {
if m.state.Cas(n, n-1) {
break
} else {
runtime.Gosched()
}
} else {
break
}
}
// Reading lock unlocks, it then only check the blocked writers.
// Note that it is not necessary to check the pending readers here.
// <n == 1> means the state of mutex comes down to zero.
if n == 1 {
if n = m.writer.Val(); n > 0 {
if m.writer.Cas(n, n-1) {
m.writing <- struct{}{}
}
}
}
}
// TryRLock tries locking the mutex for reading purpose.
// It returns true immediately if success, or if there's a writing lock on the mutex,
// it returns false immediately.
func (m *Mutex) TryRLock() bool {
var n int32
for {
if n = m.state.Val(); n >= 0 {
if m.state.Cas(n, n+1) {
return true
} else {
runtime.Gosched()
}
} else {
return false
}
}
}
// IsLocked checks whether the mutex is locked with writing or reading lock.
// Note that the result might be changed after it's called,
// so it cannot be the criterion for atomic operations.
func (m *Mutex) IsLocked() bool {
return m.state.Val() != 0
}
// IsWLocked checks whether the mutex is locked by writing lock.
// Note that the result might be changed after it's called,
// so it cannot be the criterion for atomic operations.
func (m *Mutex) IsWLocked() bool {
return m.state.Val() < 0
}
// IsRLocked checks whether the mutex is locked by reading lock.
// Note that the result might be changed after it's called,
// so it cannot be the criterion for atomic operations.
func (m *Mutex) IsRLocked() bool {
return m.state.Val() > 0
}
// LockFunc locks the mutex for writing with given callback function <f>.
// If there's a write/reading lock the mutex, it will blocks until the lock is released.
//
// It releases the lock after <f> is executed.
func (m *Mutex) LockFunc(f func()) {
m.Lock()
defer m.Unlock()
f()
}
// RLockFunc locks the mutex for reading with given callback function <f>.
// If there's a writing lock the mutex, it will blocks until the lock is released.
//
// It releases the lock after <f> is executed.
func (m *Mutex) RLockFunc(f func()) {
m.RLock()
defer m.RUnlock()
f()
}
// TryLockFunc tries locking the mutex for writing with given callback function <f>.
// it returns true immediately if success, or if there's a write/reading lock on the mutex,
// it returns false immediately.
//
// It releases the lock after <f> is executed.
func (m *Mutex) TryLockFunc(f func()) (result bool) {
if m.TryLock() {
result = true
defer m.Unlock()
f()
}
return
}
// TryRLockFunc tries locking the mutex for reading with given callback function <f>.
// It returns true immediately if success, or if there's a writing lock on the mutex,
// it returns false immediately.
//
// It releases the lock after <f> is executed.
func (m *Mutex) TryRLockFunc(f func()) (result bool) {
if m.TryRLock() {
result = true
defer m.RUnlock()
f()
}
return
}