爲什麼ArrayBlockingQueue對象的大小沒有更新？

Question

我在下面章節23.6 Proceducer /消費者關係的一個例子：ArrayBlockingQueue（「爪哇 - 如何編程10日）

我試圖運行的例子，但我不明白爲什麼‘buffer.size（）’不更新的開始。

我的確在消費類稍加修改。我把300米的毫秒爲Thread.sleep(Generator.nextInt(300))。 這裏是我的結果。

Producer writes 1 Buffer cells occupied: 0 
Consumer reads 1 Buffer cells occupied: 0 
Producer writes 2 Buffer cells occupied: 1 
Consumer reads 2 Buffer cells occupied: 0 
Producer writes 3 Buffer cells occupied: 1 
Consumer reads 3 Buffer cells occupied: 0 
Producer writes 4 Buffer cells occupied: 1 
Consumer reads 4 Buffer cells occupied: 0 
Producer writes 5 Buffer cells occupied: 1 
Consumer reads 5 Buffer cells occupied: 0 
Producer writes 6 Buffer cells occupied: 1 
Consumer reads 6 Buffer cells occupied: 0 
Producer writes 7 Buffer cells occupied: 1 
Consumer reads 7 Buffer cells occupied: 0 
Producer writes 8 Buffer cells occupied: 1 
Consumer reads 8 Buffer cells occupied: 0 
Producer writes 9 Buffer cells occupied: 1 
Consumer reads 9 Buffer cells occupied: 0 
Producer writes10 Buffer cells occupied: 1 
Producer done producing 
Terminating producer 
Consumer reads 10 Buffer cells occupied: 0 

Consumer reads values totaling 55 
Terminating Consumer 

這是代碼。

public class BlockingBufferTest { 
public static void main(String[] args) throws InterruptedException { 
    ExecutorService executorService = Executors.newCachedThreadPool(); 

    BlockingBuffer sharedLocation = new BlockingBuffer(); 

    executorService.execute(new Producer(sharedLocation)); 
    executorService.execute(new Consumer(sharedLocation)); 

    executorService.shutdown(); 
    executorService.awaitTermination(1, TimeUnit.MINUTES); 

} // end main method 
} // end class 

public class BlockingBuffer implements Buffer { 

private final ArrayBlockingQueue<Integer> buffer; // shared buffer 

public BlockingBuffer() { 
    buffer = new ArrayBlockingQueue<>(1); 
} 
@Override 
public void blockingPut(int value) throws InterruptedException { 
    buffer.put(value); // place value in buffer 
    System.out.printf("%s%2d\t%s%d%n", "Producer writes", value, "Buffer cells occupied: ", buffer.size()); 
} 

@Override 
public int blockingGet() throws InterruptedException { 
    int readValue = buffer.take(); // remove value from buffer 
    System.out.printf("%s %2d\t%s%d%n", "Consumer reads", readValue, "Buffer cells occupied: ", buffer.size()); 
    return readValue; 
} 
} 

public class Consumer implements Runnable { 

private static final SecureRandom generator = new SecureRandom(); 
private final Buffer sharedLocation; // reference to shared object 

public Consumer(Buffer sharedLocation) { 
    this.sharedLocation = sharedLocation; 
} // end constructor 

// stores values 1 to 10 in sharedLocation 
@Override 
public void run() { 
    int sum = 0; 
    for(int count=1; count<=10; count++) { 
     try { 
      Thread.sleep(generator.nextInt(300));// random sleep 
      sum +=sharedLocation.blockingGet(); 

     } catch (InterruptedException e) { 
      Thread.currentThread().interrupt(); 
     } 
    } // end for 

    System.out.printf("%n%s %d%n%s%n","Consumer reads values totaling", sum, "Terminating Consumer"); 
} // end run method 
} 

public class Producer implements Runnable { 

private static final SecureRandom generator = new SecureRandom(); 
private final Buffer sharedLocation; // reference to shared object 

public Producer(Buffer sharedLocation) { 
    this.sharedLocation = sharedLocation; 
} // end constructor 

// stores values 1 to 10 in sharedLocation 
@Override 
public void run() { 
    int sum = 0; 
    for(int count=1; count<=10; count++) { 
     try { 
      Thread.sleep(generator.nextInt(3000));// random sleep 
      sharedLocation.blockingPut(count); 
      sum += count; 

     } catch (InterruptedException e) { 
      Thread.currentThread().interrupt(); 
     } 
    } // end for 

    System.out.printf("Producer done producing%nTerminating producer%n"); 
} // end run method 
} 

Answer 1

這看起來像是線程排序/搶先式多任務的人工產物。

基本上生產者/消費者的每個週期都不是原子的。他們可以在一個週期中搶佔對方。

這裏例如如何操作的順序可能的工作：

Producer thread: put value    (size=1) 
Consumer thread: read value    (size=0) 
Producer thread: x1 = buffer.size() --> x1 = 0 
Producer thread: print x1 --> you observe 'Producer writes 1 Buffer cells occupied: 0' 
Consumer thread: x2 = buffer.size() --> x2 = 0 
Consumer thread: print x --> you observe 'Consumer reads 1 Buffer cells occupied: 0' 

附：它實際上有點棘手，沒有所有操作的線性排序，但只有一些組，但對於這個解釋可以