Java 8自动使用多核？ [英] Java 8 automatically using multicore?

问题描述

我在一年前做了一些关于java7多核的测试。首先我只在主线程中实现了一些计算（CPU使用率表明只有一个核心完成了所有的工作）然后我用ExecutorService实例实现了Callable。在运行它的所有核心工作。

I did some tests a year ago concerning multicore with java 7. First I implemented some calculations only in the main thread (CPU usage showed that only one core did all the work) and then I implemented Callable with an ExecutorService instance. While running it all cores where doing the work.

现在，一年后，我必须实现一个插入大量数据的小程序（使用java 8）。所有工作都在主线程中实现（没有Callable和ExecutorService），但是当我运行程序时，CPU使用情况显示，所有4个内核都是98％。

Now, one year, later I have to implement a little programm (using java 8) which interpolates a lot of data. All the work is implemented in the main thread (without Callable and ExecutorService) but when I'm running the programm the CPU usage shows me, that all 4 cores are at 98%.

java 8是否自动在所有CPU内核上分配工作？我很困惑......

So does java 8 automatically distribute the work on all CPU cores? I'm confused...

这里有一些代码......

Here some code...

MapGenerator.java

MapGenerator.java

    Region[][] regions = new Region[numOfRegions][numOfRegions];

    for(int x = 0; x < regions.length; x++){
        for(int z = 0; z < regions[x].length; z++){
            newLat = SRTMHandler.getNewLatitude(startLat, z * regionSize * 16);
            newLon = SRTMHandler.getNewLongitude(startLon, x * regionSize * 16, newLat);

            regions[x][z] = new Region(x, z, regionSize, newLat, newLon);
        }
    }

Region.java：

Region.java:

private Chunk[] chunks;    

public Region(int x, int z, int size, float startLat, float startLon){
    this.chunks = new Chunk[this.size][this.size];
    //Init stuff
    float newLat = this.startLat, newLon = this.startLon;

    for(int newX = 0; newX < this.size; newX++){
        for(int newZ = 0; newZ < this.size; newZ++){
            newLat = SRTMHandler.getNewLatitude(this.startLat, newZ * 16);
            newLon = SRTMHandler.getNewLongitude(this.startLon, newX * 16, newLat);

            this.chunks[newX][newZ] = new Chunk(this.x * this.size + newX, this.z * this.size + newZ, 16, 900, this, newLat, newLon);
        }
    }
}

Chunk.java：（SRTMHandler .getHeightForLatLon（）执行一些地理计算，然后读取字节数组中的值，没什么特别的）

Chunk.java: (SRTMHandler.getHeightForLatLon() does some geo calculations and then reads a value in a byte array, nothing special)

public Chunk(int x, int z, int size, int height, Region r, float startLat, float startLon){
    this.blocks = new Block[size][size][height];
    //Init stuff

    try {
        this.calcSurface();
        //System.out.println("Finished " + this.toString());
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

private void calcSurface() throws IOException{
    int x1 = this.x;
    int x2 = this.x + 16;
    int z1 = this.z;
    int z2 = this.z + 16;
    final int radius = 45;
    float q11 = SRTMHandler.getHeightForLatLon(SRTMHandler.getNewLatitude(this.startLat, (-1)*radius), SRTMHandler.getNewLongitude(this.startLon, (-1)*radius, this.startLat));
    float q12 = SRTMHandler.getHeightForLatLon(SRTMHandler.getNewLatitude(this.startLat, radius), SRTMHandler.getNewLongitude(this.startLon, (-1)*radius, this.startLat));
    float q21 = SRTMHandler.getHeightForLatLon(SRTMHandler.getNewLatitude(this.startLat, (-1)*radius), SRTMHandler.getNewLongitude(this.startLon, radius, this.startLon));
    float q22 = SRTMHandler.getHeightForLatLon(SRTMHandler.getNewLatitude(this.startLat, radius), SRTMHandler.getNewLongitude(this.startLon, radius, this.startLat));

    for(int x = 0; x < this.blocks.length; x++){
        for(int z = 0; z < this.blocks[x].length; z++){
            float height = Interpolation.biLerp(x, z, q11, q12, q21, q22, x1, x2, z1, z2);

            this.blocks[x][z][(int)Math.round(height)] = new Block(this.x * this.size + x, this.z * this.size + z, (int)Math.round(height), BlockType.Grass, this);
        }
    }
}

推荐答案

Java 8不会自动在所有CPU内核上分配工作，除非您的代码明确地请求它（例如通过使用并行流）。

Java 8 does not automatically distribute the work on all CPU cores, unless your code requests it explicitly (for example by using parallel streams).

在某些特殊情况下，Hotspot编译器将 auto -vectorize 代码，例如参见 JDK-6340864 。但是，自动矢量化使用特殊的 SIMD CPU指令，而不是多个CPU。

In some special cases the Hotspot compiler will auto-vectorize the code, see for example JDK-6340864. However, automatic vectorization is using special SIMD CPU instructions, not multiple CPUs.

另请参阅以下答案：

• JVM是否能够检测并行化的机会？


• 自动并行化

• Does the JVM have the ability to detect opportunities for parallelization?
• Automatic parallelization

（请注意，我重写了答案，删除了由评论更正的部分）

(Note that I rewrote the answer, removing the part which was corrected by the comments)

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