Java逃逸分析详解及代码示例

package me.stormma.gc;
/**
 * <p>Created on 2017/4/21.</p>
 *
 * @author stormma
 *
 * @title <p>逃逸分析</p>
 */
public class EscapeAnalysis {
  public static B b;
  /**
   * <p>全局变量赋值发生指针逃逸</p>
   */
  public void globalVariablePointerEscape() {
    b = new B();
  }
  /**
   * <p>方法返回引用，发生指针逃逸</p>
   * @return
   */
  public B methodPointerEscape() {
    return new B();
  }
  /**
   * <p>实例引用发生指针逃逸</p>
   */
  public void instancePassPointerEscape() {
    methodPointerEscape().printClassName(this);
  }
  class B {
    public void printClassName(EscapeAnalysis clazz) {
      System.out.println(clazz.getClass().getName());
    }
  }
}

public void method() {
  Test test = new Test();
  //处理逻辑
  ......
  test = null;
}

package me.stormma.gc;
/**
 * <p>Created on 2017/4/21.</p>
 *
 * @author stormma
 * @description: <p>内存分配比较</p>
 */
public class EscapeAnalysisTest {
  public static void alloc() {
    byte[] b = new byte[2];
    b[0] = 1;
  }
  public static void main(String[] args) {
    long b = System.currentTimeMillis();
    for (int i = 0; i < 100000000; i++) {
      alloc();
    }
    long e = System.currentTimeMillis();
    System.out.println(e - b);
  }
}

package me.stormma.gc;
/**
 * <p>Created on 2017/4/21.</p>
 *
 * @author stormma
 *
 * @description: <p>利用逃逸分析进行性能优化</p>
 */
public class EscapeAnalysisTest {
  private static class Foo {
    private int x;
    private static int counter;
    public Foo() {
      x = (++counter);
    }
  }
  public static void main(String[] args) {
    long start = System.nanoTime();
    for (int i = 0; i < 1000 * 1000 * 10; ++i) {
      Foo foo = new Foo();
    }
    long end = System.nanoTime();
    System.out.println("Time cost is " + (end - start));
  }
}

Time cost is 11012345

[GC (Allocation Failure) 33280K->408K(125952K), 0.0010344 secs]
[GC (Allocation Failure) 33688K->424K(125952K), 0.0009799 secs]
[GC (Allocation Failure) 33704K->376K(125952K), 0.0007297 secs]
[GC (Allocation Failure) 33656K->456K(159232K), 0.0014817 secs]
Time cost is 68562263