[GitHub] yzang commented on issue #913: Refactor FileInfo locking and refcounting out IndexPersistenceMgr

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yzang commented on issue #913: Refactor FileInfo locking and refcounting out IndexPersistenceMgr
URL: https://github.com/apache/bookkeeper/pull/913#issuecomment-355202205
 
 
   @ivankelly After taking a look at your latest change, I still have some questions. Could you help me understand how your latest change resolve the race condition?
   
   Based on my understanding, the following race condition could still happen:
   1. Current status: FileInfo f is cached in both write cache and read cache, so the refCount=2.
   2. Somehow FileInfo f is evicted from write cache, now refCount = 1.
   3. Thread A call getFileInfo() for read, so it get f from read cache at line 221, it hasn't been able to do tryRetain() yet. Now refCount = 1
   4. Thread B at the same time is evicting f from read cache, in handleLedgerEviction it will call fi.release, in the release() function "if (refCount.decrementAndGet() == 0) {" will decrement the refCount, so now refCount = 0, and "releaseFileInfo(ledgerId, this)" will be called. 
   5. Thread B call fileInfo.markDead(), since refCount ==0 is true, it returns true. So now thread B close the FileInfo f.
   6. Thread A continues, it reach tryRetain with refCount =0, and successfully return true.
   7. Thread A returns the FileInfo which is already closed.

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