缓存行
- CPU缓存是以缓存行为单位存储的;
- 缓存行是2的整数幂个连续字节,一般为32-256个字节;
- 最常见的缓存行大小是64字节;
伪共享
- 当多个线程修改相互独立的变量时,如果这些变量共享同一个缓存行,就是伪共享;
消除伪共享
Sequence消除缓存行的实现
class LhsPadding
{
protected long p1, p2, p3, p4, p5, p6, p7;
}
class Value extends LhsPadding
{
protected volatile long value;
}
class RhsPadding extends Value
{
protected long p9, p10, p11, p12, p13, p14, p15;
}
public class Sequence extends RhsPadding
{
static final long INITIAL_VALUE = -1L;
private static final Unsafe UNSAFE;
private static final long VALUE_OFFSET;
static
{
UNSAFE = Util.getUnsafe();
try
{
VALUE_OFFSET = UNSAFE.objectFieldOffset(Value.class.getDeclaredField("value"));
}
catch (final Exception e)
{
throw new RuntimeException(e);
}
}
}