loom的jtreg测试VirtualThreadPinnedEventThrows.java无法移植到KonaFiber-8的原因分析

[ywj0101]

VirtualThreadPinnedEventThrows.java 代码分析

源码链接：https://github.com/openjdk/loom/blob/bf5d8122254115c81f026aff8fe882c22612feb5/test/jdk/java/lang/Thread/virtual/VirtualThreadPinnedEventThrows.java

jtreg 的 test description 说明

/**
 * @test
 * @summary Test parking when pinned and emitting the JFR VirtualThreadPinnedEvent throws
 * @modules java.base/jdk.internal.event
 * @compile/module=java.base jdk/internal/event/VirtualThreadPinnedEvent.java
 * @run junit VirtualThreadPinnedEventThrows
 */

关于这个描述，重要的地方在与@compile/module=java.base jdk/internal/event/VirtualThreadPinnedEvent.java。表示执行该jtreg测试时，会优先编译java.base中jdk/internal/event/VirtualThreadPinnedEvent.java，及代码（https://github.com/openjdk/loom/blob/bf5d8122254115c81f026aff8fe882c22612feb5/test/jdk/java/lang/Thread/virtual/java.base/jdk/internal/event/VirtualThreadPinnedEvent.java ）。因此在执行测试时，如果调用 VirtualThreadPinnedEvent 中的方法时，会调用该文件中的方法，而不是JDK中默认的 VirtualThreadPinnedEvent.java（在jdk22中位于jdk.internal.event 包下）。

核心方法 testParkWhenPinned 分析

/**
     * Test parking a virtual thread when pinned.
     */
    private void testParkWhenPinned() throws Exception {
        Object lock = new Object();
        try {
            var completed = new AtomicBoolean();
            Thread thread = Thread.startVirtualThread(() -> {
                synchronized (lock) {
                    LockSupport.park();
                    completed.set(true);
                }
            });

            // wait for thread to park
            Thread.State state;
            while ((state = thread.getState()) != Thread.State.WAITING) {
                assertTrue(state != Thread.State.TERMINATED);
                Thread.sleep(10);
            }

            // unpark and check that thread completed without exception
            LockSupport.unpark(thread);
            thread.join();
            assertTrue(completed.get());
        } finally {
            Reference.reachabilityFence(lock);
        }
    }

该方法主要用于触发 VirtualThreadPinnedEvent，在虚拟线程中，需要满足两个触发条件

1. 持有锁，代码中使用synchronized (lock) 实现
2. 虚拟线程处于 WAITING 状态

在触发 VirtualThreadPinnedEvent 后，唤醒虚拟线程，等待执行完毕。代码执行期间对虚拟线程的状态以及 completed 变量进行了断言

测试方法分析

/**
 * Test parking when pinned and creating the VirtualThreadPinnedEvent fails with OOME.
 */
@Test
void testVirtualThreadPinnedEventCreateThrows() throws Exception {
    VirtualThreadPinnedEvent.setCreateThrows(true);
    try {
        testParkWhenPinned();
    } finally {
        VirtualThreadPinnedEvent.setCreateThrows(false);
    }
}

/**
 * Test parking when pinned and VirtualThreadPinnedEvent.begin fails with OOME.
 */
@Test
void testVirtualThreadPinnedEventBeginThrows() throws Exception {
    VirtualThreadPinnedEvent.setBeginThrows(true);
    try {
        testParkWhenPinned();
    } finally {
        VirtualThreadPinnedEvent.setBeginThrows(false);
    }
}

/**
 * Test parking when pinned and VirtualThreadPinnedEvent.commit fails with OOME.
 */
@Test
void testVirtualThreadPinnedEventCommitThrows() throws Exception {
    VirtualThreadPinnedEvent.setCommitThrows(true);
    try {
        testParkWhenPinned();
    } finally {
        VirtualThreadPinnedEvent.setCommitThrows(false);
    }
}

总共有三个Test，每个 Test 都是为了测试 VirtualThreadPinnedEvent 触发失败，只是失败的阶段不同，分别是 VirtualThreadPinnedEvent 的 create、begin、commit阶段。

测试可能存在的缺陷

在 testParkWhenPinned 方法中，无法证明 VirtualThreadPinnedEvent 是否因为 OOME 而触发失败，因为在jdk22中，VirtualThread中已经捕获了OutOfMemoryError，见下面代码

private void parkOnCarrierThread(boolean timed, long nanos) {
        assert state() == RUNNING;

        VirtualThreadPinnedEvent event;
        try {
            event = new VirtualThreadPinnedEvent();
            event.begin();
        } catch (OutOfMemoryError e) {
            event = null;
        }

对测试的改进

因为OOME已经在 VirtualThread 中的 parkOnCarrierThread 方法捕获，并且将 event 设置为空，所以无法收集到 VirtualThreadPinnedEvent ，从而证明抛出了OOME，对 testParkWhenPinned 方法修改如下：

/**
     * Test parking a virtual thread when pinned.
     */
    private void testParkWhenPinned() throws Exception {
        try (Recording recording = new Recording()) {
            // 开启事件
            recording.enable("jdk.VirtualThreadPinned");
            recording.start();

            Object lock = new Object();
            try {
                var completed = new AtomicBoolean();
                Thread thread = Thread.startVirtualThread(() -> {
                    synchronized (lock) {
                        LockSupport.park();
                        completed.set(true);
                    }
                });

                // wait for thread to park
                Thread.State state;
                while ((state = thread.getState()) != Thread.State.WAITING) {
                    assertTrue(state != Thread.State.TERMINATED);
                    Thread.sleep(10);
                }

                // unpark and check that thread completed without exception
                LockSupport.unpark(thread);
                thread.join();
                assertTrue(completed.get());
            } finally {
                Reference.reachabilityFence(lock);
            }

            recording.stop();

            Map<String, Integer> events = sumEvents(recording);
            int virtualThreadPinnedEventCount = events.getOrDefault("jdk.VirtualThreadPinned", 0);
            assertEquals(0, virtualThreadPinnedEventCount);
        }
    }

使用 JFR 收集jdk.VirtualThreadPinned 是否发生，通过assertEquals(0, virtualThreadPinnedEventCount);断言收集不到该事件

测试移植至kona失败的原因分析

JDK22 和kona 8中对虚拟线程触发的事件定义方式不同。在jdk22中 VirtualThreadPinnedEvent 的类被映射到 jdk.internal.event.VirtualThreadPinnedEvent 位置，代码如下

@Category("Java Application")
@Label("Virtual Thread Pinned")
@Name("jdk.VirtualThreadPinned")
@MirrorEvent(className = "jdk.internal.event.VirtualThreadPinnedEvent")
public final class VirtualThreadPinnedEvent extends AbstractJDKEvent {
}

而在kona 8 中，该 VirtualThreadPinnedEvent 被写死，无法对VirtualThreadPinnedEvent进行修改，代码如下

@Category({"Java Runtime"})
@Label("Virtual thread pinned")
@Name("jdk.VirtualThreadPinned")
@Description("Virtual thread pinned")
public final class VirtualThreadPinnedEvent extends AbstractJDKEvent {
}

因此无法移植。