基于 AbstractQueuedSynchronizer 的并发类实现
Posted 张宏杰
tags:
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公平模式ReentrantLock实现原理
前面的文章研究了AbstractQueuedSynchronizer的独占锁和共享锁，有了前两篇文章的基础，就可以乘胜追击，看一下基于AbstractQueuedSynchronizer的并发类是如何实现的。
ReentrantLock显然是一种独占锁，首先是公平模式的ReentrantLock，Sync是ReentractLock中的基础类，继承自AbstractQueuedSynchronizer，看一下代码实现：
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abstract
static
class
Sync
extends
AbstractQueuedSynchronizer
private
static
final
long
serialVersionUID = -5179523762034025860L;
/**
* Performs @link Lock#lock. The main reason for subclassing
* is to allow fast path for nonfair version.
*/
abstract
void
lock();
/**
* Performs non-fair tryLock. tryAcquire is
* implemented in subclasses, but both need nonfair
* try for trylock method.
*/
final
boolean
nonfairTryAcquire(
int
acquires)
final
Thread current = Thread.currentThread();
int
c = getState();
if
(c ==
0
)
if
(compareAndSetState(
0
, acquires))
setExclusiveOwnerThread(current);
return
true
;
else
if
(current == getExclusiveOwnerThread())
int
nextc = c + acquires;
if
(nextc <
0
)
// overflow
throw
new
Error(
"Maximum lock count exceeded"
);
setState(nextc);
return
true
;
return
false
;
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