Question

我已经实现了Java Filter lock，如下所示：

public class Filter implements Lock {
int[] level;
int[] victim;
int n;

public Filter(int n) {
    this.n = n;
    level = new int[n];
    victim = new int[n];
}

@Override
public void lock() {
    int me = ConcurrencyUtils.getCurrentThreadId();
    for (int i = 1; i < n; i++) {
        level[me] = i;
        victim[i] = me;

        boolean conflicts = true;
        while (conflicts) {
            conflicts = false;
            for (int k = 0; k < n; k++) {
                if (k != me && level[k] >= i && victim[i] == me) {
                    conflicts = true;
                    break;
                }
            }
        }
    }
}

@Override
public void unlock() {
    int me = ConcurrencyUtils.getCurrentThreadId();
    level[me] = 0;
}
...
}

n和ConcurrencyUtils.getCurrentThreadId()返回自定义线程ID（线程最终将从0开始）。

这是我的自定义计数器类，用于比较实现runnable的性能：

public long getAndIncrement() {
    long temp;
    lock.lock();
    try {
        if (value >= maxNumber) {
            return value;
        }
        temp = value;
        value = temp + 1;
    } finally {
        lock.unlock();
    }
    return temp;
}

@Override
public void run() {
    while (getAndIncrement() < maxNumber) {
        //do nothing
    }
}

这是我的AlgorithmRunner类的性能比较部分：

    Thread[] threads = new Thread[threadCount];
    long threadNumber = 0;

    long startTime = System.nanoTime();

    for (int i = 0; i < threads.length; i++) {
        threads[i] = new Thread(counter);
        threads[i].setName(String.valueOf(threadNumber++));
    }        

    for (Thread thread : threads) {
        thread.start();
    }

    for (Thread thread : threads) {
        thread.join();
    }

    long finishTime = System.nanoTime();

    return TimeUnit.NANOSECONDS.toMillis(finishTime - startTime);

每当我使用大于3的线程数运行它时，它就会挂起。我的意思是它循环很长时间（也许是无限的），它实际上并没有挂起。它在锁定循环内运行。似乎lock方法有问题（当我将Thread sleep置于锁定状态时，我可以看到它最多可以运行5个线程。）

但是，对于少于3的情况，它是可以的。我将自定义锁定与Java的ReentrantLock进行比较。它可以在很短的时间内完成所有工作，即使像往常一样有更多的线程。

我在实施时想念的是什么？

PS 1：我已经按照“多处理艺术图书”的说法进行了示例。

PS 2：以下是挂起时的线程转储：

Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.60-b09 mixed mode):

"2" prio=10 tid=0x00007f4c6837f000 nid=0x76ff runnable [0x00007f4c4dc8a000]
   java.lang.Thread.State: RUNNABLE
    at org.oocp.filter.Filter.lock(Filter.java:33)
    at org.oocp.Counter.getAndIncrement(Counter.java:50)
    at org.oocp.Counter.run(Counter.java:65)
    at java.lang.Thread.run(Thread.java:745)

"1" prio=10 tid=0x00007f4c68379000 nid=0x76fe runnable [0x00007f4c4db89000]
   java.lang.Thread.State: RUNNABLE
    at org.oocp.filter.Filter.lock(Filter.java:33)
    at org.oocp.Counter.getAndIncrement(Counter.java:50)
    at org.oocp.Counter.run(Counter.java:65)
    at java.lang.Thread.run(Thread.java:745)

"0" prio=10 tid=0x00007f4c68378800 nid=0x76fd runnable [0x00007f4c4dd8b000]
   java.lang.Thread.State: RUNNABLE
    at org.oocp.filter.Filter.lock(Filter.java:33)
    at org.oocp.Counter.getAndIncrement(Counter.java:50)
    at org.oocp.Counter.run(Counter.java:65)
    at java.lang.Thread.run(Thread.java:745)

"Service Thread" daemon prio=10 tid=0x00007f4c681e6800 nid=0x7608 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" daemon prio=10 tid=0x00007f4c681e4000 nid=0x7607 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" daemon prio=10 tid=0x00007f4c681e1000 nid=0x7606 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" daemon prio=10 tid=0x00007f4c681df800 nid=0x7605 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" daemon prio=10 tid=0x00007f4c681bf800 nid=0x7604 in Object.wait() [0x00007f4c4efee000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000007db310398> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:135)
    - locked <0x00000007db310398> (a java.lang.ref.ReferenceQueue$Lock)
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:151)
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)

"Reference Handler" daemon prio=10 tid=0x00007f4c681bd800 nid=0x7603 in Object.wait() [0x00007f4c4f0ef000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000007db310440> (a java.lang.ref.Reference$Lock)
    at java.lang.Object.wait(Object.java:503)
    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)
    - locked <0x00000007db310440> (a java.lang.ref.Reference$Lock)

"main" prio=10 tid=0x00007f4c68009800 nid=0x75f9 in Object.wait() [0x00007f4c701c4000]
   java.lang.Thread.State: WAITING (on object monitor)
    at java.lang.Object.wait(Native Method)
    - waiting on <0x00000007d7014ad0> (a java.lang.Thread)
    at java.lang.Thread.join(Thread.java:1281)
    - locked <0x00000007d7014ad0> (a java.lang.Thread)
    at java.lang.Thread.join(Thread.java:1355)
    at org.oocp.AlgorithmRunner.runTest(AlgorithmRunner.java:45)
    at org.oocp.AlgorithmRunner.runStatistics(AlgorithmRunner.java:63)
    at org.oocp.AlgorithmRunner.main(AlgorithmRunner.java:24)

"VM Thread" prio=10 tid=0x00007f4c681b9000 nid=0x7602 runnable 

"GC task thread#0 (ParallelGC)" prio=10 tid=0x00007f4c6801f800 nid=0x75fa runnable 

"GC task thread#1 (ParallelGC)" prio=10 tid=0x00007f4c68021800 nid=0x75fb runnable 

"GC task thread#2 (ParallelGC)" prio=10 tid=0x00007f4c68023000 nid=0x75fc runnable 

"GC task thread#3 (ParallelGC)" prio=10 tid=0x00007f4c68025000 nid=0x75fd runnable 

"GC task thread#4 (ParallelGC)" prio=10 tid=0x00007f4c68027000 nid=0x75fe runnable 

"GC task thread#5 (ParallelGC)" prio=10 tid=0x00007f4c68029000 nid=0x75ff runnable 

"GC task thread#6 (ParallelGC)" prio=10 tid=0x00007f4c6802a800 nid=0x7600 runnable 

"GC task thread#7 (ParallelGC)" prio=10 tid=0x00007f4c6802c800 nid=0x7601 runnable 

"VM Periodic Task Thread" prio=10 tid=0x00007f4c681f1000 nid=0x7609 waiting on condition 

JNI global references: 236

Heap
 PSYoungGen      total 68608K, used 22516K [0x00000007d7000000, 0x00000007db800000, 0x0000000800000000)
  eden space 63488K, 33% used [0x00000007d7000000,0x00000007d84f5308,0x00000007dae00000)
  from space 5120K, 20% used [0x00000007db300000,0x00000007db408010,0x00000007db800000)
  to   space 5120K, 0% used [0x00000007dae00000,0x00000007dae00000,0x00000007db300000)
 ParOldGen       total 83968K, used 16K [0x0000000785000000, 0x000000078a200000, 0x00000007d7000000)
  object space 83968K, 0% used [0x0000000785000000,0x0000000785004000,0x000000078a200000)
 PSPermGen       total 21504K, used 6588K [0x000000077fe00000, 0x0000000781300000, 0x0000000785000000)
  object space 21504K, 30% used [0x000000077fe00000,0x000000078046f0c0,0x0000000781300000)

Answer 1

我能找到错误的地方。关键是：

Java编程语言不保证可线性化，或者在读取或写入共享字段时甚至是顺序一致性对象[1]。

因此，对于我的level和victim数组，我使用了AtomicInteger而不是int：

AtomicInteger[] level;
AtomicInteger[] victim;

[1]多处理器编程的艺术。 Maurice Herlihy，Nir Shavit，2008，pp.61。

Java过滤器锁实现挂起

1 个答案: