/
mutex.go
82 lines (69 loc) · 2.24 KB
/
mutex.go
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// Copyright (c) 2017 Uber Technologies, Inc.
//
// 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 tracing
import (
"context"
"fmt"
"sync"
"github.com/opentracing/opentracing-go"
"github.com/opentracing/opentracing-go/log"
)
// Mutex is just like the standard sync.Mutex, except that it is aware of the Context
// and logs some diagnostic information into the current span.
type Mutex struct {
SessionBaggageKey string
realLock sync.Mutex
holder string
waiters []string
waitersLock sync.Mutex
}
// Lock acquires an exclusive lock.
func (sm *Mutex) Lock(ctx context.Context) {
var session string
activeSpan := opentracing.SpanFromContext(ctx)
if activeSpan != nil {
session = activeSpan.BaggageItem(sm.SessionBaggageKey)
activeSpan.SetTag(sm.SessionBaggageKey, session)
}
sm.waitersLock.Lock()
if waiting := len(sm.waiters); waiting > 0 && activeSpan != nil {
activeSpan.LogFields(
log.String("event", fmt.Sprintf("Waiting for lock behind %d transactions", waiting)),
log.String("blockers", fmt.Sprintf("%v", sm.waiters))) // avoid deferred slice.String()
fmt.Printf("%s Waiting for lock behind %d transactions: %v\n", session, waiting, sm.waiters)
}
sm.waiters = append(sm.waiters, session)
sm.waitersLock.Unlock()
sm.realLock.Lock()
sm.holder = session
sm.waitersLock.Lock()
behindLen := len(sm.waiters) - 1
sm.waitersLock.Unlock()
if activeSpan != nil {
activeSpan.LogEvent(
fmt.Sprintf("Acquired lock with %d transactions waiting behind", behindLen))
}
}
// Unlock releases the lock.
func (sm *Mutex) Unlock() {
sm.waitersLock.Lock()
for i, v := range sm.waiters {
if v == sm.holder {
sm.waiters = append(sm.waiters[0:i], sm.waiters[i+1:]...)
break
}
}
sm.waitersLock.Unlock()
sm.realLock.Unlock()
}