hadoop中使用的Unsafe.java

今天查看hadoop源代码， 发现有个Unsafe.java

稍微总结下

优势 1 减少线程调度开销， Unsafe.java 通过采用非堵塞原子方式来减少线程调度开销
        2 传统线程通信通过wait,notify方法实现(会有信号量的堵塞队列)，而Unsafe使用操作系统调度命令park,unpark， 减少信号量的开销，提高新能。

差不多和windows下的InterlockedDecrement差不多的概念， 只是Unsafe的功能更加强大，可以获取的类型更多，另外可以有C/C++方式的内存分配模式以及内存交换等更多操作

Java中不直接使用Unsafe.java，封装成原子类给用户使用

public class AtomicInteger extends Number implements java.io.Serializable {
    private static final long serialVersionUID = 6214790243416807050L;

    // setup to use Unsafe.compareAndSwapInt for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;

其他还有很多类型.

附源代码

/*** Eclipse Class Decompiler plugin, copyright (c) 2012 Chao Chen (cnfree2000@hotmail.com) ***/
package sun.misc;

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.security.ProtectionDomain;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;

public final class Unsafe
{
  private static final Unsafe theUnsafe;
  public static final int INVALID_FIELD_OFFSET = -1;
  public static final int ARRAY_BOOLEAN_BASE_OFFSET;
  public static final int ARRAY_BYTE_BASE_OFFSET;
  public static final int ARRAY_SHORT_BASE_OFFSET;
  public static final int ARRAY_CHAR_BASE_OFFSET;
  public static final int ARRAY_INT_BASE_OFFSET;
  public static final int ARRAY_LONG_BASE_OFFSET;
  public static final int ARRAY_FLOAT_BASE_OFFSET;
  public static final int ARRAY_DOUBLE_BASE_OFFSET;
  public static final int ARRAY_OBJECT_BASE_OFFSET;
  public static final int ARRAY_BOOLEAN_INDEX_SCALE;
  public static final int ARRAY_BYTE_INDEX_SCALE;
  public static final int ARRAY_SHORT_INDEX_SCALE;
  public static final int ARRAY_CHAR_INDEX_SCALE;
  public static final int ARRAY_INT_INDEX_SCALE;
  public static final int ARRAY_LONG_INDEX_SCALE;
  public static final int ARRAY_FLOAT_INDEX_SCALE;
  public static final int ARRAY_DOUBLE_INDEX_SCALE;
  public static final int ARRAY_OBJECT_INDEX_SCALE;
  public static final int ADDRESS_SIZE;

  private static native void registerNatives();

  @CallerSensitive
  public static Unsafe getUnsafe()
  {
    Class localClass = Reflection.getCallerClass();
    if (localClass.getClassLoader() != null)
      throw new SecurityException("Unsafe");
    return theUnsafe;
  }

  public native int getInt(Object paramObject, long paramLong);

  public native void putInt(Object paramObject, long paramLong, int paramInt);

  public native Object getObject(Object paramObject, long paramLong);

  public native void putObject(Object paramObject1, long paramLong, Object paramObject2);

  public native boolean getBoolean(Object paramObject, long paramLong);

  public native void putBoolean(Object paramObject, long paramLong, boolean paramBoolean);

  public native byte getByte(Object paramObject, long paramLong);

  public native void putByte(Object paramObject, long paramLong, byte paramByte);

  public native short getShort(Object paramObject, long paramLong);

  public native void putShort(Object paramObject, long paramLong, short paramShort);

  public native char getChar(Object paramObject, long paramLong);

  public native void putChar(Object paramObject, long paramLong, char paramChar);

  public native long getLong(Object paramObject, long paramLong);

  public native void putLong(Object paramObject, long paramLong1, long paramLong2);

  public native float getFloat(Object paramObject, long paramLong);

  public native void putFloat(Object paramObject, long paramLong, float paramFloat);

  public native double getDouble(Object paramObject, long paramLong);

  public native void putDouble(Object paramObject, long paramLong, double paramDouble);

  @Deprecated
  public int getInt(Object paramObject, int paramInt)
  {
    return getInt(paramObject, paramInt);
  }

  @Deprecated
  public void putInt(Object paramObject, int paramInt1, int paramInt2)
  {
    putInt(paramObject, paramInt1, paramInt2);
  }

  @Deprecated
  public Object getObject(Object paramObject, int paramInt)
  {
    return getObject(paramObject, paramInt);
  }

  @Deprecated
  public void putObject(Object paramObject1, int paramInt, Object paramObject2)
  {
    putObject(paramObject1, paramInt, paramObject2);
  }

  @Deprecated
  public boolean getBoolean(Object paramObject, int paramInt)
  {
    return getBoolean(paramObject, paramInt);
  }

  @Deprecated
  public void putBoolean(Object paramObject, int paramInt, boolean paramBoolean)
  {
    putBoolean(paramObject, paramInt, paramBoolean);
  }

  @Deprecated
  public byte getByte(Object paramObject, int paramInt)
  {
    return getByte(paramObject, paramInt);
  }

  @Deprecated
  public void putByte(Object paramObject, int paramInt, byte paramByte)
  {
    putByte(paramObject, paramInt, paramByte);
  }

  @Deprecated
  public short getShort(Object paramObject, int paramInt)
  {
    return getShort(paramObject, paramInt);
  }

  @Deprecated
  public void putShort(Object paramObject, int paramInt, short paramShort)
  {
    putShort(paramObject, paramInt, paramShort);
  }

  @Deprecated
  public char getChar(Object paramObject, int paramInt)
  {
    return getChar(paramObject, paramInt);
  }

  @Deprecated
  public void putChar(Object paramObject, int paramInt, char paramChar)
  {
    putChar(paramObject, paramInt, paramChar);
  }

  @Deprecated
  public long getLong(Object paramObject, int paramInt)
  {
    return getLong(paramObject, paramInt);
  }

  @Deprecated
  public void putLong(Object paramObject, int paramInt, long paramLong)
  {
    putLong(paramObject, paramInt, paramLong);
  }

  @Deprecated
  public float getFloat(Object paramObject, int paramInt)
  {
    return getFloat(paramObject, paramInt);
  }

  @Deprecated
  public void putFloat(Object paramObject, int paramInt, float paramFloat)
  {
    putFloat(paramObject, paramInt, paramFloat);
  }

  @Deprecated
  public double getDouble(Object paramObject, int paramInt)
  {
    return getDouble(paramObject, paramInt);
  }

  @Deprecated
  public void putDouble(Object paramObject, int paramInt, double paramDouble)
  {
    putDouble(paramObject, paramInt, paramDouble);
  }

  public native byte getByte(long paramLong);

  public native void putByte(long paramLong, byte paramByte);

  public native short getShort(long paramLong);

  public native void putShort(long paramLong, short paramShort);

  public native char getChar(long paramLong);

  public native void putChar(long paramLong, char paramChar);

  public native int getInt(long paramLong);

  public native void putInt(long paramLong, int paramInt);

  public native long getLong(long paramLong);

  public native void putLong(long paramLong1, long paramLong2);

  public native float getFloat(long paramLong);

  public native void putFloat(long paramLong, float paramFloat);

  public native double getDouble(long paramLong);

  public native void putDouble(long paramLong, double paramDouble);

  public native long getAddress(long paramLong);

  public native void putAddress(long paramLong1, long paramLong2);

  public native long allocateMemory(long paramLong);

  public native long reallocateMemory(long paramLong1, long paramLong2);

  public native void setMemory(Object paramObject, long paramLong1, long paramLong2, byte paramByte);

  public void setMemory(long paramLong1, long paramLong2, byte paramByte)
  {
    setMemory(null, paramLong1, paramLong2, paramByte);
  }

  public native void copyMemory(Object paramObject1, long paramLong1, Object paramObject2, long paramLong2, long paramLong3);

  public void copyMemory(long paramLong1, long paramLong2, long paramLong3)
  {
    copyMemory(null, paramLong1, null, paramLong2, paramLong3);
  }

  public native void freeMemory(long paramLong);

  @Deprecated
  public int fieldOffset(Field paramField)
  {
    if (Modifier.isStatic(paramField.getModifiers())) {
      return (int)staticFieldOffset(paramField);
    }
    return (int)objectFieldOffset(paramField);
  }

  @Deprecated
  public Object staticFieldBase(Class paramClass)
  {
    Field[] arrayOfField = paramClass.getDeclaredFields();
    for (int i = 0; i < arrayOfField.length; ++i) {
      if (Modifier.isStatic(arrayOfField[i].getModifiers())) {
        return staticFieldBase(arrayOfField[i]);
      }
    }
    return null;
  }

  public native long staticFieldOffset(Field paramField);

  public native long objectFieldOffset(Field paramField);

  public native Object staticFieldBase(Field paramField);

  public native boolean shouldBeInitialized(Class<?> paramClass);

  public native void ensureClassInitialized(Class paramClass);

  public native int arrayBaseOffset(Class paramClass);

  public native int arrayIndexScale(Class paramClass);

  public native int addressSize();

  public native int pageSize();

  public native Class defineClass(String paramString, byte[] paramArrayOfByte, int paramInt1, int paramInt2, ClassLoader paramClassLoader, ProtectionDomain paramProtectionDomain);

  @Deprecated
  @CallerSensitive
  public native Class defineClass(String paramString, byte[] paramArrayOfByte, int paramInt1, int paramInt2);

  public native Class defineAnonymousClass(Class paramClass, byte[] paramArrayOfByte, Object[] paramArrayOfObject);

  public native Object allocateInstance(Class paramClass)
    throws InstantiationException;

  public native void monitorEnter(Object paramObject);

  public native void monitorExit(Object paramObject);

  public native boolean tryMonitorEnter(Object paramObject);

  public native void throwException(Throwable paramThrowable);

  public final native boolean compareAndSwapObject(Object paramObject1, long paramLong, Object paramObject2, Object paramObject3);

  public final native boolean compareAndSwapInt(Object paramObject, long paramLong, int paramInt1, int paramInt2);

  public final native boolean compareAndSwapLong(Object paramObject, long paramLong1, long paramLong2, long paramLong3);

  public native Object getObjectVolatile(Object paramObject, long paramLong);

  public native void putObjectVolatile(Object paramObject1, long paramLong, Object paramObject2);

  public native int getIntVolatile(Object paramObject, long paramLong);

  public native void putIntVolatile(Object paramObject, long paramLong, int paramInt);

  public native boolean getBooleanVolatile(Object paramObject, long paramLong);

  public native void putBooleanVolatile(Object paramObject, long paramLong, boolean paramBoolean);

  public native byte getByteVolatile(Object paramObject, long paramLong);

  public native void putByteVolatile(Object paramObject, long paramLong, byte paramByte);

  public native short getShortVolatile(Object paramObject, long paramLong);

  public native void putShortVolatile(Object paramObject, long paramLong, short paramShort);

  public native char getCharVolatile(Object paramObject, long paramLong);

  public native void putCharVolatile(Object paramObject, long paramLong, char paramChar);

  public native long getLongVolatile(Object paramObject, long paramLong);

  public native void putLongVolatile(Object paramObject, long paramLong1, long paramLong2);

  public native float getFloatVolatile(Object paramObject, long paramLong);

  public native void putFloatVolatile(Object paramObject, long paramLong, float paramFloat);

  public native double getDoubleVolatile(Object paramObject, long paramLong);

  public native void putDoubleVolatile(Object paramObject, long paramLong, double paramDouble);

  public native void putOrderedObject(Object paramObject1, long paramLong, Object paramObject2);

  public native void putOrderedInt(Object paramObject, long paramLong, int paramInt);

  public native void putOrderedLong(Object paramObject, long paramLong1, long paramLong2);

  public native void unpark(Object paramObject);

  public native void park(boolean paramBoolean, long paramLong);

  public native int getLoadAverage(double[] paramArrayOfDouble, int paramInt);

  static
  {
    registerNatives();
    Reflection.registerMethodsToFilter(Unsafe.class, new String[] { "getUnsafe" });

    theUnsafe = new Unsafe();

    ARRAY_BOOLEAN_BASE_OFFSET = theUnsafe.arrayBaseOffset([Z.class);

    ARRAY_BYTE_BASE_OFFSET = theUnsafe.arrayBaseOffset([B.class);

    ARRAY_SHORT_BASE_OFFSET = theUnsafe.arrayBaseOffset([S.class);

    ARRAY_CHAR_BASE_OFFSET = theUnsafe.arrayBaseOffset([C.class);

    ARRAY_INT_BASE_OFFSET = theUnsafe.arrayBaseOffset([I.class);

    ARRAY_LONG_BASE_OFFSET = theUnsafe.arrayBaseOffset([J.class);

    ARRAY_FLOAT_BASE_OFFSET = theUnsafe.arrayBaseOffset([F.class);

    ARRAY_DOUBLE_BASE_OFFSET = theUnsafe.arrayBaseOffset([D.class);

    ARRAY_OBJECT_BASE_OFFSET = theUnsafe.arrayBaseOffset([Ljava.lang.Object.class);

    ARRAY_BOOLEAN_INDEX_SCALE = theUnsafe.arrayIndexScale([Z.class);

    ARRAY_BYTE_INDEX_SCALE = theUnsafe.arrayIndexScale([B.class);

    ARRAY_SHORT_INDEX_SCALE = theUnsafe.arrayIndexScale([S.class);

    ARRAY_CHAR_INDEX_SCALE = theUnsafe.arrayIndexScale([C.class);

    ARRAY_INT_INDEX_SCALE = theUnsafe.arrayIndexScale([I.class);

    ARRAY_LONG_INDEX_SCALE = theUnsafe.arrayIndexScale([J.class);

    ARRAY_FLOAT_INDEX_SCALE = theUnsafe.arrayIndexScale([F.class);

    ARRAY_DOUBLE_INDEX_SCALE = theUnsafe.arrayIndexScale([D.class);

    ARRAY_OBJECT_INDEX_SCALE = theUnsafe.arrayIndexScale([Ljava.lang.Object.class);

    ADDRESS_SIZE = theUnsafe.addressSize();
  }
}