boom-java/src/main/java/me/giraffetree/java/boomjava/jvm/jmm/UnsafePublication.java at master · giraffe-tree/boom-java · GitHub

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package me.giraffetree.java.boomjava.jvm.jmm;

import org.openjdk.jcstress.annotations.Actor;
import org.openjdk.jcstress.annotations.Description;
import org.openjdk.jcstress.annotations.Expect;
import org.openjdk.jcstress.annotations.JCStressTest;
import org.openjdk.jcstress.annotations.Outcome;
import org.openjdk.jcstress.annotations.State;
import org.openjdk.jcstress.infra.results.I_Result;


/**
 * code from http://hg.openjdk.java.net/code-tools/jcstress/file/64f2cf32fa0a/tests-custom/src/main/java/org/openjdk/jcstress/tests/unsafe/UnsafePublication.java
 * run:
 * main class: org.openjdk.jcstress.Main
 * args: -v -t me.giraffetree.java.boomjava.jvm.jmm.UnsafePublication
 *
 * out:
 * Observed state   Occurrences   Expectation  Interpretation
 * -1     4,679,668    ACCEPTABLE  The object is not yet published
 * 0             0    ACCEPTABLE  The object is published, but all fields are 0.
 * 1             0    ACCEPTABLE  The object is published, at least 1 field is visible.
 * 2             0    ACCEPTABLE  The object is published, at least 2 fields are visible.
 * 3             0    ACCEPTABLE  The object is published, at least 3 fields are visible.
 * 4    38,754,332    ACCEPTABLE  The object is published, all fields are visible.
 * 说明在 object 在new 的时候
 * 分配一块内存 M；将 M 的地址赋值给 instance 变量；最后在内存 M 上初始化 Singleton 对象。
 * 先赋值了地址, 后初始化对象
 * 导致了 obj = null
 */
@JCStressTest
@Description("Tests if unsafe publication is unsafe.")
@Outcome(id = "-1", expect = Expect.ACCEPTABLE_INTERESTING, desc = "The object is not yet published")
@Outcome(id = "0", expect = Expect.ACCEPTABLE, desc = "The object is published, but all fields are 0.")
@Outcome(id = "1", expect = Expect.ACCEPTABLE, desc = "The object is published, at least 1 field is visible.")
@Outcome(id = "2", expect = Expect.ACCEPTABLE, desc = "The object is published, at least 2 fields are visible.")
@Outcome(id = "3", expect = Expect.ACCEPTABLE, desc = "The object is published, at least 3 fields are visible.")
@Outcome(id = "4", expect = Expect.ACCEPTABLE, desc = "The object is published, all fields are visible.")
@State
public class UnsafePublication {

    /*
       Implementation notes:
         * This showcases how compiler can move the publishing store past the field stores.
         * We need to provide constructor with some external value. If we put the constants in the
           constructor, then compiler can store all the fields with a single bulk store.
         * This test is best to be run with either 32-bit VM, or 64-bit VM with -XX:-UseCompressedOops:
           it seems the compressed references mechanics moves the reference store after the field
           stores, even though not required by JMM.
     */

    int x = 1;

    MyObject o;

    @Actor
    public void publish() {
        o = new MyObject(x);
    }

    @Actor
    public void consume(I_Result res) {
        MyObject lo = o;
        if (lo != null) {
            res.r1 = lo.x00 + lo.x01 + lo.x02 + lo.x03;
        } else {
            res.r1 = -1;
        }
    }

    static class MyObject {
        int x00, x01, x02, x03;

        public MyObject(int x) {
            x00 = x;
            x01 = x;
            x02 = x;
            x03 = x;
        }
    }

}