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rwmutex_trylock.go
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rwmutex_trylock.go
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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
/*
$ 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
*/
}