David Goldblatt 26c792e61a Allow mutexes to take a lock ordering enum at construction.
This lets us specify whether and how mutexes of the same rank are allowed to be
acquired.  Currently, we only allow two polices (only a single mutex at a given
rank at a time, and mutexes acquired in ascending order), but we can plausibly
allow more (e.g. the "release uncontended mutexes before blocking").
2017-05-19 14:21:27 -07:00
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