java被关于ReentrantReadWriteLock#tryLock失败的jcstress测试弄糊涂了

Question

我正在努力克服压力。为了确保我理解它，我决定为一些我知道必须正确的东西编写一些简单的测试：java.util.concurrent.locks.ReentrantReadWriteLock

我编写了一些非常简单的测试来检查锁模式兼容性。不幸的是，有两项压力测试失败：

1. X_S：

   true, true        32,768     FORBIDDEN  No default case provided, assume FORBIDDEN
   

2. X_X：

   true, true        32,767     FORBIDDEN  No default case provided, assume FORBIDDEN
   

在我看来，一个线程不应该拥有读锁，而另一个线程也拥有写锁。同样，两个线程不可能同时持有写锁

我意识到问题可能不在ReentrantReadWriteLock。我想我可能在jcmstress测试中犯了一些愚蠢的错误，比如JMM和读取锁的状态

不幸的是，我无法发现这个问题。谁能帮我理解这个（愚蠢的？）我犯的错误

import org.openjdk.jcstress.annotations.*;
import org.openjdk.jcstress.infra.results.ZZ_Result;

import java.util.concurrent.locks.ReentrantReadWriteLock;

/*
 * |-----------------|
 * |  COMPATIBILITY  |
 * |-----------------|
 * |     | S   | X   |
 * |-----------------|
 * | S   | YES | NO  |
 * | X   | NO  | NO  |
 * |-----------------|
 */
public class ReentrantReadWriteLockBooleanCompatibilityTest {

    @State
    public static class S {
        public final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

        public boolean shared() {
            return lock.readLock().tryLock();
        }

        public boolean exclusive() {
            return lock.writeLock().tryLock();
        }
    }

    @JCStressTest
    @Outcome(id = "true, true", expect = Expect.ACCEPTABLE, desc = "T1 and T2 are both acquired S")
    public static class S_S {
        @Actor
        public void actor1(S s, ZZ_Result r) { r.r1 = s.shared(); }
        @Actor
        public void actor2(S s, ZZ_Result r) { r.r2 = s.shared(); }
    }

    @JCStressTest
    @Outcome(id = "true, false", expect = Expect.ACCEPTABLE, desc = "T1 acquired S, and T2 could not acquire X")
    @Outcome(id = "false, true", expect = Expect.ACCEPTABLE, desc = "T2 acquired X, and T1 could not acquire S")
    public static class S_X {
        @Actor
        public void actor1(S s, ZZ_Result r) { r.r1 = s.shared(); }
        @Actor
        public void actor2(S s, ZZ_Result r) { r.r2 = s.exclusive(); }
    }

    @JCStressTest
    @Outcome(id = "true, false", expect = Expect.ACCEPTABLE, desc = "T1 acquired X, and T2 could not acquire S")
    @Outcome(id = "false, true", expect = Expect.ACCEPTABLE, desc = "T2 acquired S and T1 could not acquire X")
    public static class X_S {
        @Actor
        public void actor1(S s, ZZ_Result r) { r.r1 = s.exclusive(); }
        @Actor
        public void actor2(S s, ZZ_Result r) { r.r2 = s.shared(); }
    }

    @JCStressTest
    @Outcome(id = "true, false", expect = Expect.ACCEPTABLE, desc = "T1 acquired X, and T2 could not acquire X")
    @Outcome(id = "false, true", expect = Expect.ACCEPTABLE, desc = "T2 acquired X and T1 could not acquire X")
    public static class X_X {
        @Actor
        public void actor1(S s, ZZ_Result r) { r.r1 = s.exclusive(); }
        @Actor
        public void actor2(S s, ZZ_Result r) { r.r2 = s.exclusive(); }
    }
}

我确实试着在jcstress-dev上询问过这件事，但从未收到回复-http://mail.openjdk.java.net/pipermail/jcstress-dev/2018-August/000346.html。很抱歉交叉发布，但我需要帮助，所以我将转载到StackOverflow，希望能引起更多观众的注意

Answer 1

在JC0.3下运行时，测试通过。在版本0.4中，行为改变为包括启动时运行的健全性检查的结果（参见针对错误的jcstress omits samples gathered during sanity checks）

一些健全性检查在单个线程中运行，并且您的测试不会处理两个参与者都被同一线程调用的情况；您正在测试一个可重入锁，因此如果已经持有写锁，则读锁将通过

这可以说是jcstress中的一个bug，因为@Actor上的文档说不变量是：

• Each method is called only by one particular thread.
• Each method is called exactly once per State instance.

虽然文档的措辞不是很清楚，但生成的源代码清楚地表明，目的是在自己的线程中运行每个参与者

解决此问题的一种方法是允许单螺纹壳体通过：

@State
public static class S {
    public final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

    public boolean shared() {
        return lock.readLock().tryLock();
    }

    public boolean exclusive() {
        return lock.writeLock().tryLock();
    }

    public boolean locked() {
        return lock.isWriteLockedByCurrentThread();
    }
}

@JCStressTest
@Outcome(id = "true, false, false", expect = Expect.ACCEPTABLE, desc = "T1 acquired X, and T2 could not acquire S")
@Outcome(id = "false, false, true", expect = Expect.ACCEPTABLE, desc = "T2 acquired S and T1 could not acquire X")
@Outcome(id = "true, true, true", expect = Expect.ACCEPTABLE, desc = "T1 acquired X and then acquired S")
public static class X_S {
    @Actor
    public void actor1(S s, ZZZ_Result r) {
        r.r1 = s.exclusive();
    }
    @Actor
    public void actor2(S s, ZZZ_Result r) {
        r.r2 = s.locked();
        r.r3 = s.shared();
    }
}

或者检查单螺纹外壳，并将其标记为“有趣”而不是“接受”：

@State
public static class S {
    public final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    public AtomicReference<Thread> firstThread = new AtomicReference<>();

    public boolean shared() {
        firstThread.compareAndSet(null, Thread.currentThread());
        return lock.readLock().tryLock();
    }

    public boolean exclusive() {
        firstThread.compareAndSet(null, Thread.currentThread());
        return lock.writeLock().tryLock();
    }

    public boolean sameThread() {
        return Thread.currentThread().equals(firstThread.get());
    }

    public boolean locked() {
        return lock.isWriteLockedByCurrentThread();
    }
}

@JCStressTest
@Outcome(id = "false, true, false, false", expect = Expect.ACCEPTABLE, desc = "T1 acquired X, and T2 could not acquire X")
@Outcome(id = "false, false, false, true", expect = Expect.ACCEPTABLE, desc = "T2 acquired X and T1 could not acquire X")
@Outcome(id = "false, true, true, true", expect = Expect.ACCEPTABLE_INTERESTING, desc = "Both actors ran in the same thread!")
@Outcome(id = "true, true, false, true", expect = Expect.ACCEPTABLE_INTERESTING, desc = "Both actors ran in the same thread!")
public static class X_X {
    @Actor
    public void actor1(S s, ZZZZ_Result r) {
        r.r1 = s.sameThread();
        r.r2 = s.exclusive();
    }
    @Actor
    public void actor2(S s, ZZZZ_Result r) {
        r.r3 = s.sameThread();
        r.r4 = s.exclusive();
    }
}

正如您在评论中所指出的，上述测试中的最终@Outcome从未发生过。这是因为单线程健全性检查在运行参与者之前不会对其进行洗牌（请参阅生成的测试类上的方法sanityCheck_Footprints）