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                合規國際互聯網加速 OSASE為企業客戶提供高速穩定SD-WAN國際加速解決方案。 廣告
                Compare And Swap 簡稱CAS (比較并交換) 先比較變量的值是否等于給定舊值,等于舊值的情況下才賦予新值,最后返回新值是否設置成功。 使用鎖的做法趨于悲觀 我們總假設會有并發的操作要修改被操作的值,并使用鎖將相關操作放入臨界區中加以保護。 使用CAS操作的做法趨于樂觀 總是假設被操作值未曾被改變(即與舊值相等),并一旦確認這個假設的真實性就立即進行值替換。 ~~~ package main import( "fmt" "sync" "sync/atomic" ) func main(){ var sum uint32 = 100 var wg sync.WaitGroup for i := uint32(0); i < 100; i++ { wg.Add(1) go func(t uint32) { defer wg.Done() atomic.CompareAndSwapUint32(&sum, 100, sum+1) }(i) } wg.Wait() fmt.Println(sum) } ~~~ 輸出結果: ~~~ 101 ~~~ 可以看到sum的值只改變了一次,只有當sum值為100的時候,CAS才將sum的值修改為了sum+1。 函數原型: ~~~ atomic.CompareAndSwapUint32(addr *uint32, old, new uint32) bool atomic.CompareAndSwapUint64(addr *uint64, old, new uint64) bool atomic.CompareAndSwapInt32(addr *int32, old, new int32) bool atomic.CompareAndSwapInt64(addr *int64, old, new int64) bool atomic.CompareAndSwapUintptr(addr *uintptr, old, new uintptr) bool atomic.CompareAndSwapPointer(addr *unsafe.Pointer, old, new unsafe.Pointer) bool ~~~
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