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mutex.go
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// Copyright 2015-2018 trivago N.V.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package tsync
import (
"sync/atomic"
)
// Mutex is a lightweight, spinner based mutex implementation, extending the
// standard go mutex by the possibility to query the mutex' state and by adding
// a TryLock function.
type Mutex struct {
state *int32
priority SpinPriority
}
const (
mutexUnlocked = int32(0)
mutexLocked = int32(1)
)
// NewMutex creates a new mutex with the given spin priority used during Lock.
func NewMutex(priority SpinPriority) *Mutex {
return &Mutex{
state: new(int32),
priority: priority,
}
}
// Lock blocks (spins) until the lock becomes available
func (m *Mutex) Lock() {
spin := NewSpinner(m.priority)
for !m.TryLock() {
spin.Yield()
}
}
// TryLock tries to acquire a lock and returns true if it succeeds. This
// function does not block.
func (m *Mutex) TryLock() bool {
return atomic.CompareAndSwapInt32(m.state, mutexUnlocked, mutexLocked)
}
// Unlock unblocks one routine waiting on lock.
func (m *Mutex) Unlock() {
atomic.StoreInt32(m.state, mutexUnlocked)
}
// IsLocked returns the state of this mutex. The result of this function might
// change directly after call so it should only be used in situations where
// this fact is not considered problematic.
func (m *Mutex) IsLocked() bool {
return atomic.LoadInt32(m.state) != mutexUnlocked
}