test/jdk/java/lang/Thread/virtual/BigStackChunk.java

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/*
 * @test id=default
 * @bug 8335362
 * @summary Test virtual thread usage with big stackChunks
 * @requires vm.continuations
 * @run junit/othervm BigStackChunk
 */

import java.util.concurrent.locks.ReentrantLock;

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

class BigStackChunk {

    void recurse(int cnt, ReentrantLock rlock) {
        int i1 = cnt;
        int i2 = i1 + 1;
        int i3 = i2 + 1;
        int i4 = i3 + 1;
        int i5 = i4 + 1;
        int i6 = i5 + 1;
        int i7 = i6 + 1;
        long ll = 2 * (long)i1;
        float ff = ll + 1.2f;
        double dd = ff + 1.3D;

        if (cnt > 0) {
            recurse(cnt - 1, rlock);
        } else {
            rlock.lock();
            rlock.unlock();
        }
    }

    @Test
    void bigStackChunkTest() throws Exception {
        int VTHREAD_CNT = Runtime.getRuntime().availableProcessors();
        ReentrantLock rlock = new ReentrantLock();
        Thread[] vthreads = new Thread[VTHREAD_CNT];

        rlock.lock();
        for (int i = 0; i < VTHREAD_CNT; i++) {
            vthreads[i] = Thread.ofVirtual().start(() -> {
                // Set up things so that half of the carriers will commit lots of
                // pages in the stack while running the mounted vthread and half
                // will just commit very few ones.
                if (Math.random() < 0.5) {
                    recurse(300, rlock);
                } else {
                    recurse(1, rlock);
                }
            });
        }
        await(vthreads[0], Thread.State.WAITING);
        // Now we expect that some vthread that recursed a lot is mounted on
        // a carrier that previously run a vthread that didn't recurse at all.
        rlock.unlock();

        for (int i = 0; i < VTHREAD_CNT; i++) {
            vthreads[i].join();
        }
    }

    private void await(Thread thread, Thread.State expectedState) throws InterruptedException {
        Thread.State state = thread.getState();
        while (state != expectedState) {
            assertTrue(state != Thread.State.TERMINATED, "Thread has terminated");
            Thread.sleep(10);
            state = thread.getState();
        }
    }
}