Java AtomicReferenceArray weakCompareAndSet()用法及代碼示例

如果當前值等於作為參數傳遞的ExpectedValue，則使用AtomicReferenceArray類的weakCompareAndSet()方法以原子方式將AtomicReferenceArray的索引i處的元素值設置為newValue到newValue。此方法使用讀取的內存語義更新索引i的值，就好像該變量被聲明為變量的易失性類型一樣。如果成功將AtomicReference設置為新值，則此方法返回true。

用法:

public final boolean
       weakCompareAndSet(
           int i, E expectedValue, E newValue)

參數：此方法接受：

i這是執行操作的AtomicReferenceArray的索引，
expectedValue 這是期望值，
newValue 這是要設置的新值。

返回值：如果成功將AtomicReference設置為新值，則此方法返回true。

以下示例程序旨在說明weakCompareAndSet()方法：
程序1:

// Java program to demonstrate 
// weakCompareAndSet() method 
  
import java.util.concurrent.atomic.*; 
  
public class GFG { 
  
    public static void main(String[] args) 
    { 
  
        // create an atomic reference object. 
        AtomicReferenceArray<Integer> ref 
            = new AtomicReferenceArray<Integer>(5); 
  
        // set some value 
        ref.set(0, 543); 
        ref.set(1, 124); 
        ref.set(2, 322); 
  
        // apply weakCompareAndSet() 
        boolean result 
            = ref.weakCompareAndSet(0, 124, 
                                    234); 
  
        // print value 
        System.out.println("Setting new value"
                           + " is successful = "
                           + result); 
  
        System.out.println("Value of index 0 = "
                           + ref.get(0)); 
    } 
}

輸出：

Setting new value is successful = false
Value of index 0 = 543

程序2:

// Java program to demonstrate 
// weakCompareAndSet() method 
  
import java.util.concurrent.atomic.*; 
  
public class GFG { 
  
    public static void main(String[] args) 
    { 
  
        // create an atomic reference object.c 
        AtomicReferenceArray<String> ref 
            = new AtomicReferenceArray<String>(5); 
  
        // set some value 
        ref.set(0, "INDIA"); 
        ref.set(1, "US"); 
        ref.set(2, "UK"); 
        ref.set(3, "CHINA"); 
        ref.set(4, "CHINA"); 
  
        // apply weakCompareAndSet() 
        boolean result 
            = ref.weakCompareAndSet(4, "CHINA", 
                                    "CANADA"); 
  
        // print value 
        System.out.println("Setting new value"
                           + " is successful = "
                           + result); 
  
        System.out.println("Value of index 4 = "
                           + ref.get(4)); 
    } 
}

輸出：

Setting new value is successful = true
Value of index 4 = CANADA

參考文獻： https://docs.oracle.com/javase/10/docs/api/java/util/concurrent/atomic/AtomicReferenceArray.html#weakCompareAndSet(V, V)

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