Summary: Ref T13202. See PHI889. If the lock log is enabled, we can try to offer more details about lock holders. When we fail to acquire a lock: - check for recent acquisitions and suggest that this is a bottleneck issue; - if there are no recent acquisitions, check for the last acquisition and print details about it (what process, how long ago, whether or not we believe it was released). Test Plan: - Enabled the lock log. - Changed the lock wait time to 1 second. - Added a `sleep(10)` after grabbing the lock. - In one window, ran a Conduit call or a `git fetch`. - In another window, ran another operation. - Got useful/sensible errors for both ssh and web lock holders, for example: > PhutilProxyException: Failed to acquire read lock after waiting 1 second(s). You may be able to retry later. (This lock was most recently acquired by a process (pid=12609, host=orbital-3.local, sapi=apache2handler, controller=PhabricatorConduitAPIController, method=diffusion.rawdiffquery) 3 second(s) ago. There is no record of this lock being released.) > PhutilProxyException: Failed to acquire read lock after waiting 1 second(s). You may be able to retry later. (This lock was most recently acquired by a process (pid=65251, host=orbital-3.local, sapi=cli, argv=/Users/epriestley/dev/core/lib/phabricator/bin/ssh-exec --phabricator-ssh-device local.phacility.net --phabricator-ssh-key 2) 2 second(s) ago. There is no record of this lock being released.) Reviewers: amckinley Reviewed By: amckinley Maniphest Tasks: T13202 Differential Revision: https://secure.phabricator.com/D19702