tree 447f5103cfb02aadba1f2a3b5e9ece5d4e92d581
parent e5effef428b5bf941e1697f6000c97f1ce734756
author Jason Evans <jasone@canonware.com> 1476386318 -0700
committer Jason Evans <jasone@canonware.com> 1476398220 -0700

Make dss operations lockless.

Rather than protecting dss operations with a mutex, use atomic
operations.  This has negligible impact on synchronization overhead
during typical dss allocation, but is a substantial improvement for
extent_in_dss() and the newly added extent_dss_mergeable(), which can be
called multiple times during extent deallocations.

This change also has the advantage of avoiding tsd in deallocation paths
associated with purging, which resolves potential deadlocks during
thread exit due to attempted tsd resurrection.

This resolves #425.