[GitHub] [mina-sshd] tomaswolf opened a new pull request, #238: [SSHD-1289] Fix lock handling in KeyExchangeMessageHandler

[GitBox <gi...@apache.org>]

tomaswolf opened a new pull request, #238:
URL: https://github.com/apache/mina-sshd/pull/238

   Make sure that a thread does not try to acquire the write lock if
   it already holds the read lock. This could happen if a write is not
   enqueued and there is an exception during writing, and we then try
   to close the session on the same thread.
   
   The read/write lock is used for three purposes: first, it gives the
   flushing thread trying to empty the queue of pending packets priority
   over other threads trying to enqueue more packets, and second, it is
   held during writeOrEnqueue() while writing a packet directly to prevent
   that the KEX state changes between being checked and the write being
   done, and third, to prevent that the KEX state changes asynchronously
   while the flushing thread is checking it. The read/write lock itself
   does not serve to ensure mutual exclusion on the KEX state itself.
   
   These three functions can also be fulfilled if update() is executed
   when only the read lock is held. If a thread in update() holds the read
   lock, this can only occur if it wrote the buffer directly in
   writeOrEnqueue(), in which case it is fine to proceed, and the flushing
   thread for sure is not in its critical region where it holds the write
   lock. Otherwise, any other thread either is the flushing thread and
   holds the write lock already, or it's a thread not holding the lock at
   all. In both cases it is fine to acquire the write lock.


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[GitHub] [mina-sshd] tomaswolf merged pull request #238: [SSHD-1289] Fix lock handling in KeyExchangeMessageHandler

[GitBox <gi...@apache.org>]

tomaswolf merged PR #238:
URL: https://github.com/apache/mina-sshd/pull/238


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