ReentrantLock 原理分析

public void lock()

先看公平鎖的lock函式

final void lock()

public final void acquire(int arg)

protected final boolean tryacquire(int acquires) 

}//如果狀態不為0，則判斷是否為已經獲得鎖的物件進行重入鎖操作
else if (current == getexclusiveownerthread()) 
//獲取鎖失敗返回false
return false;
}

public final boolean hasqueuedpredecessors()

protected final boolean compareandsetstate(int expect, int update)

這兩步完成以後，就可以將當前執行緒標記為獨佔執行緒，該執行緒釋放鎖之前，再有執行緒來嘗試獲取鎖都會進入下一步acquirequeued(addwaiter(node.exclusive), arg)

先看addwaiter

private node addwaiter(node mode) 

}enq(node);
return node;
}

private node enq(final node node)  else }}

}

final boolean acquirequeued(final node node, int arg) 

if (shouldparkafte***iledacquire(p, node) &&
parkandcheckinterrupt())
interrupted = true;
}} finally 
}

先看parkandcheckinterrupt

private final boolean parkandcheckinterrupt()

然後是shouldparkafte***iledacquire

private static boolean shouldparkafte***iledacquire(node pred, node node)  while (pred.waitstatus > 0);

pred.next = node;
} else 
return false;
}

final void lock()

他的acquire也跟公平鎖不同

protected final boolean tryacquire(int acquires)

final boolean nonfairtryacquire(int acquires) 

}else if (current == getexclusiveownerthread()) 
return false;
}

public void unlock()

public final boolean release(int arg) 

return false;
}

protected final boolean tryrelease(int releases) 

setstate(c);
return free;
}

private void unparksuccessor(node node) 

if (s != null)
locksupport.unpark(s.thread);
}

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