指令级并行是什么

指令级并行（ILP）指通过通过流水线等技术实现多条指令同时并行执行的并行技术
实现ILP主要的方法有：

• 依靠硬件动态发现和开发并行

• 依靠软件在编译时静态发现并行

  实例

  引入pom
  使用jcstress来进行大数据量测试

    <dependencies>
        <dependency>
            <groupId>org.openjdk.jcstress</groupId>
            <artifactId>jcstress-core</artifactId>
            <version>${jcstress.version}</version>
        </dependency>
    </dependencies>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <!--
            jcstress version to use with this project.
          -->
        <jcstress.version>0.5</jcstress.version>
        <!--
            Java source/target to use for compilation.
          -->
        <javac.target>1.8</javac.target>
        <!--
            Name of the test Uber-JAR to generate.
          -->
        <uberjar.name>jcstress</uberjar.name>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <compilerVersion>${javac.target}</compilerVersion>
                    <source>${javac.target}</source>
                    <target>${javac.target}</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.2</version>
                <executions>
                    <execution>
                        <id>main</id>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <finalName>${uberjar.name}</finalName>
                            <transformers>
                                <transformer
                                        implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>org.openjdk.jcstress.Main</mainClass>
                                </transformer>
                                <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
                                    <resource>META-INF/TestList</resource>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

  I_Result是结果集，ACCEPTABLE_INTERESTING是我们推测的最极端条件下产生的结果，也就是可见性
  。 ```java import org.openjdk.jcstress.annotations.*; import org.openjdk.jcstress.infra.results.I_Result;

@JCStressTest @Outcome(id = {“1”, “4”}, expect = Expect.ACCEPTABLE, desc = “ok”) @Outcome(id = “0”, expect = Expect.ACCEPTABLE_INTERESTING, desc = “!!!!”) @State public class ConcurrencyTest {

int num = 0;
boolean ready = false;
@Actor
public void actor1(I_Result r) {
    if(ready) {
        r.r1 = num + num;
    } else {
        r.r1 = 1;
    }
}
@Actor
public void actor2(I_Result r) {
    num = 2;
    ready = true;
}

}

打包后<br />![image.png](https://cdn.nlark.com/yuque/0/2022/png/22478710/1647189067543-496a76b7-d39f-4ef3-876e-f715a4a0307d.png#clientId=u1774d5b7-86f9-4&crop=0&crop=0&crop=1&crop=1&from=paste&height=369&id=u3a935e9e&margin=%5Bobject%20Object%5D&name=image.png&originHeight=581&originWidth=840&originalType=binary&ratio=1&rotation=0&showTitle=false&size=156524&status=done&style=none&taskId=u3657f65d-f552-4361-87de-1f334b68f99&title=&width=533.3333575536345)<br />在CMD中输入 java -jar target/jcstress.jar -t cn.itcast.ConcurrencyTest<br />触发了58次这个可见性的结果<br />![image.png](https://cdn.nlark.com/yuque/0/2022/png/22478710/1647189347813-b06a112d-5579-47c9-b9b5-0d2154a0ed11.png#clientId=u1774d5b7-86f9-4&crop=0&crop=0&crop=1&crop=1&from=paste&height=244&id=u752a18af&margin=%5Bobject%20Object%5D&name=image.png&originHeight=384&originWidth=1702&originalType=binary&ratio=1&rotation=0&showTitle=false&size=282165&status=done&style=none&taskId=uec72d4a0-bec9-45bb-969a-da375157305&title=&width=1080.6349697098642)
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# 解决方案
```java
import org.openjdk.jcstress.annotations.*;
import org.openjdk.jcstress.infra.results.I_Result;
@JCStressTest
@Outcome(id = {"1", "4"}, expect = Expect.ACCEPTABLE, desc = "ok")
@Outcome(id = "0", expect = Expect.ACCEPTABLE_INTERESTING, desc = "!!!!")
@State
public class ConcurrencyTest {
    int num = 0;
    volatile boolean ready = false;
    @Actor
    public void actor1(I_Result r) {
        if(ready) {
            r.r1 = num + num;
        } else {
            r.r1 = 1;
        }
    }
    @Actor
    public void actor2(I_Result r) {
        num = 2;
        ready = true;
    }
}

重新运行后：
就没有出现可见性问题了。