Goメモ-497 (RWMutex.TryLock/TryRLock)(ロック取得をノンブロッキングに)

概要

以下、自分用のメモです。

前回、Mutex.TryLock についてメモしたのですが、sync.RWMutex についても RWMutex.TryLock、RWMutex.TryRLock が追加されています。使い方は同じです。

サンプル

rwmutex_trylock.go

package syncs

import (
    "context"
    "log"
    "sync"
    "time"
)

// RWMutexTryLock は、Go 1.18 で追加された RWMutex の TryLock() と TryRLock() のサンプルです。
//
// 使い方としては、Mutex.TryLock() と同じ。RLockのTry版がTryRLock, LockのTry版がTryLockとなる。
//
// # REFERENCES
//   - https://pkg.go.dev/sync@go1.22.1#RWMutex.TryLock
//   - https://pkg.go.dev/sync@go1.22.1#RWMutex.TryRLock
func RWMutexTryLock() error {
    //
    // 3つのゴルーチンがあり、２つは値の読み取り(RLock)、１つは値の書き込み(Lock)を行う。
    // それぞれ、ロックに入る前に TryRLock/TryLock により、ロック可能かどうかを確認する。
    //

    log.SetFlags(log.Lmicroseconds)

    var (
        v    int64
        m    sync.RWMutex
        read = func(ctx context.Context, prefix string, interval time.Duration) {
            for {
                select {
                case <-ctx.Done():
                    return
                default:
                }

                func() {
                    log.Printf("[%s] <<<", prefix)
                    for !m.TryRLock() {
                        log.Printf("[%s] TryRLock=false", prefix)

                        select {
                        case <-ctx.Done():
                            return
                        case <-time.After(100 * time.Millisecond):
                        }
                    }

                    log.Printf("[%s] %v", prefix, v)

                    m.RUnlock()
                    log.Printf("[%s] >>>", prefix)

                    select {
                    case <-ctx.Done():
                    case <-time.After(interval):
                    }
                }()
            }
        }
        write = func(ctx context.Context, prefix string, interval time.Duration) {
            for {
                select {
                case <-ctx.Done():
                    return
                default:
                }

                func() {
                    log.Printf("[%s] <<<", prefix)
                    for !m.TryLock() {
                        log.Printf("[%s] TryLock=false", prefix)

                        select {
                        case <-ctx.Done():
                            return
                        case <-time.After(100 * time.Millisecond):
                        }
                    }

                    old := v
                    v++
                    log.Printf("[%s] %v --> %v", prefix, old, v)

                    m.Unlock()
                    log.Printf("[%s] >>>", prefix)

                    select {
                    case <-ctx.Done():
                    case <-time.After(interval):
                    }
                }()
            }
        }
    )

    ctx, cxl := context.WithTimeout(context.Background(), 2*time.Second)
    defer cxl()

    go read(ctx, "READ-1", 500*time.Millisecond)
    go read(ctx, "READ-2", 500*time.Millisecond)
    go write(ctx, "WRITE-1", 500*time.Millisecond)

    <-ctx.Done()
    log.Println("DONE")

    return nil
}

実行

$ task
task: [build] go build .
task: [run] ./try-golang -onetime

ENTER EXAMPLE NAME: syncs_rwmutex_trylock

[Name] "syncs_rwmutex_trylock"
06:00:30.134950 [WRITE-1] <<<
06:00:30.135052 [WRITE-1] 0 --> 1
06:00:30.135059 [WRITE-1] >>>
06:00:30.134976 [READ-2] <<<
06:00:30.135079 [READ-2] 1
06:00:30.135085 [READ-2] >>>
06:00:30.134970 [READ-1] <<<
06:00:30.135264 [READ-1] 1
06:00:30.135268 [READ-1] >>>
06:00:30.635750 [READ-1] <<<
06:00:30.635773 [READ-1] 1
06:00:30.635776 [READ-1] >>>
06:00:30.635762 [READ-2] <<<
06:00:30.635803 [READ-2] 1
06:00:30.635812 [READ-2] >>>
06:00:30.635787 [WRITE-1] <<<
06:00:30.635855 [WRITE-1] 1 --> 2
06:00:30.635867 [WRITE-1] >>>
06:00:31.136388 [WRITE-1] <<<
06:00:31.136406 [READ-1] <<<
06:00:31.136411 [WRITE-1] 2 --> 3
06:00:31.136423 [WRITE-1] >>>
06:00:31.136422 [READ-2] <<<
06:00:31.136430 [READ-2] 3
06:00:31.136438 [READ-2] >>>
06:00:31.136415 [READ-1] TryRLock=false
06:00:31.236739 [READ-1] 3
06:00:31.236767 [READ-1] >>>
06:00:31.637314 [WRITE-1] <<<
06:00:31.637340 [READ-2] <<<
06:00:31.637367 [READ-2] TryRLock=false
06:00:31.637335 [WRITE-1] 3 --> 4
06:00:31.637405 [WRITE-1] >>>
06:00:31.737604 [READ-2] 4
06:00:31.737631 [READ-2] >>>
06:00:31.737631 [READ-1] <<<
06:00:31.737644 [READ-1] 4
06:00:31.737653 [READ-1] >>>
06:00:32.135034 DONE


[Elapsed] 2.000177751s