背景

JCStress（Java Concurrency Stress Tests）是一个用于测试和验证Java并发程序正确性的工具。它是OpenJDK项目的一部分，旨在帮助开发人员发现并发程序中的竞态条件、死锁、内存可见性等问题。

JCStress提供了一组注解和API，使得编写并发测试变得简单和方便。使用JCStress，您可以定义和运行各种类型的并发测试，包括多线程竞争测试、内存可见性测试、有序性测试等。JCStress会自动执行大量的并发测试用例，并生成详细的测试报告，以帮助您分析和理解并发程序的行为。

JCStress的主要特点包括：

• 并发测试：JCStress支持编写各种类型的并发测试，包括竞争条件测试、死锁测试、内存可见性测试等。
• 自动化测试：JCStress会自动执行大量的并发测试用例，并尝试发现潜在的并发问题。
• 测试报告：JCStress生成详细的测试报告，包括测试结果、执行时间、线程状态等信息，以帮助您分析并发程序的行为。
• 高度可配置：JCStress提供了丰富的配置选项，如线程数、迭代次数、测试模式等，以满足不同类型的并发测试需求。

JCStress使用

使用JCStress编写和运行并发测试的一般步骤包括：

• 在测试类或测试方法上使用JCStress提供的注解，如@JCStressTest、@Actor、@Outcome等，来定义并发测试。
• 使用JCStress提供的命令行工具或API来运行并发测试，并指定相关的选项和参数。
• 分析和解释JCStress生成的测试报告，以发现并发问题并进行修复。

JCStress使用示例

测试用例1：

/*
    This is our first concurrency test. It is deliberately simplistic to show
    testing approaches, introduce JCStress APIs, etc.

    Suppose we want to see if the field increment is atomic. We can make test
    with two actors, both actors incrementing the field and recording what
    value they observed into the result object. As JCStress runs, it will
    invoke these methods on the objects holding the field once per each actor
    and instance, and record what results are coming from there.

    Done enough times, we will get the history of observed results, and that
    would tell us something about the concurrent behavior.

    How to run this test:
       $ java -jar jcstress-samples/target/jcstress.jar -t API_01_Simple

       ...

        .......... [OK] org.openjdk.jcstress.samples.api.API_01_Simple

          Scheduling class:
            actor1: package group 0, core group 0
            actor2: package group 0, core group 0

          CPU allocation:
            actor1: CPU #3, package #0, core #3
            actor2: CPU #35, package #0, core #3

          Compilation: split
            actor1: C2
            actor2: C2

          JVM args: []

          RESULT      SAMPLES    FREQ       EXPECT  DESCRIPTION
            1, 1   46,946,789   10.1%  Interesting  Both actors came up with the same value: atomicity failure.
            1, 2  110,240,149   23.8%   Acceptable  actor1 incremented, then actor2.
            2, 1  306,529,420   66.1%   Acceptable  actor2 incremented, then actor1.
 */

// Mark the class as JCStress test.
@JCStressTest

// These are the test outcomes.
@Outcome(id = "1, 1", expect = ACCEPTABLE_INTERESTING, desc = "Both actors came up with the same value: atomicity failure.")
@Outcome(id = "1, 2", expect = ACCEPTABLE, desc = "actor1 incremented, then actor2.")
@Outcome(id = "2, 1", expect = ACCEPTABLE, desc = "actor2 incremented, then actor1.")

// This is a state object
@State
public class API_01_Simple {

    int v;

    @Actor
    public void actor1(II_Result r) {
        r.r1 = ++v; // record result from actor1 to field r1
    }

    @Actor
    public void actor2(II_Result r) {
        r.r2 = ++v; // record result from actor2 to field r2
    }

}

测试用例2：

@JCStressTest
@Outcome(id = {"1, 2", "2, 1"}, expect = ACCEPTABLE, desc = "Mutex works")
@Outcome(id = "1, 1",           expect = FORBIDDEN,  desc = "Mutex failure")
@State
public class Mutex_06_Semaphore {

    /*
        How to run this test:
            $ java -jar jcstress-samples/target/jcstress.jar -t Mutex_06_Semaphore
    */

    /*
      ----------------------------------------------------------------------------------------------------------

        Single-permit Semaphore can be used as a crude mutex too. Of course, this primitive
        is much more flexible, it can admit a few threads at once with more permits.

        On x86_64, AArch64, PPC64:
          RESULT      SAMPLES     FREQ      EXPECT  DESCRIPTION
            1, 1            0    0.00%   Forbidden  Mutex failure
            1, 2  254,394,919   50.23%  Acceptable  Mutex works
            2, 1  252,081,625   49.77%  Acceptable  Mutex works
     */

    private final Semaphore semaphore = new Semaphore(1);
    private int v;

    @Actor
    public void actor1(II_Result r) {
        try {
            semaphore.acquire();
            // critical section
            r.r1 = ++v;
            semaphore.release();
        } catch (InterruptedException e) {
            throw new IllegalStateException(e);
        }
    }

    @Actor
    public void actor2(II_Result r) {
        try {
            semaphore.acquire();
            // critical section
            r.r2 = ++v;
            semaphore.release();
        } catch (InterruptedException e) {
            throw new IllegalStateException(e);
        }
    }
}

JCStress总结

JCStress是一个强大的工具，可以帮助开发人员测试和验证Java并发程序的正确性。它广泛应用于Java开发社区，并被认为是Java并发测试领域的事实标准。使用JCStress可以提高并发程序的质量和可靠性，减少并发问题的出现。

参考资料：

【1】https://github.com/openjdk/jcstress/tree/master/jcstress-samples/src/main/java/org/openjdk/jcstress/samples。