Alexander Motin c809a67a72 Replace locks added in r260229 to protect sequence counters with atomics.
New algorithm does not create additional lock congestion, while some races
it includes should not be a problem.  Those races may keep requests in DRC
cache for some more time by returning ACK position smaller then actual,
but it still should be able to drop thems when proper ACK finally read.

Races of the original algorithm based on TCP seq number were worse because
they happened when reply sequence number were recorded. After that even
correctly read ACKs could not clean DRC sometimes.
2014-01-04 15:51:31 +00:00
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