併發讀取和寫入BlockingQueue

Question

我在數據庫前使用LinkedBlockingQueue。一個線程寫入隊列，另一個線程讀取隊列。

兩個併發寫入應該是不可能的我想。但是有可能一個線程寫入，另一個線程同時從隊列中讀取？如果沒有，是否有一個隊列在Java中提供這個功能？

Answer 1

是的，有可能一個線程是讀取和一個是寫入在同一時間。

LinkedBlockingQueue爲此使用兩個鎖。一個用於從隊列中取物品，另一個用於放置物品。

/** Lock held by put, offer, etc */ 
private final ReentrantLock putLock = new ReentrantLock(); 

/** Lock held by take, poll, etc */ 
private final ReentrantLock takeLock = new ReentrantLock(); 

上LinkedBlockingQueue實現的方式也在其source file (line 77)討論。

/* 
* A variant of the "two lock queue" algorithm. The putLock gates 
* entry to put (and offer), and has an associated condition for 
* waiting puts. Similarly for the takeLock. The "count" field 
* that they both rely on is maintained as an atomic to avoid 
* needing to get both locks in most cases. Also, to minimize need 
* for puts to get takeLock and vice-versa, cascading notifies are 
* used. When a put notices that it has enabled at least one take, 
* it signals taker. That taker in turn signals others if more 
* items have been entered since the signal. And symmetrically for 
* takes signalling puts. Operations such as remove(Object) and 
* iterators acquire both locks. 
*/