Java 8自动使用多核？

Question

我在一年前做了一些关于java 7多核的测试.首先我只在主线程中实现了一些计算(CPU使用率显示只有一个核心完成所有工作)然后我用ExecutorService实例实现了Callable.在运行它时,所有核心都在进行工作.

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%.

那么java 8会自动在所有CPU内核上分配工作吗？我糊涂了...

这里有些代码......

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:

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)

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);
        }
    }
}

Answer 1

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

在某些特殊情况下,Hotspot编译器将自动对代码进行矢量化,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.

另见这些答案:

• JVM是否能够检测并行化的机会？
• 自动并行化

(请注意,我重写了答案,删除了由评论更正的部分)