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Ben Gamari authored
Summary: Currently the event manager has a global flag for whether to create epoll-like notifications as one-shot (e.g. EPOLLONESHOT, where an fd will be deactivated after its first event) or standard multi-shot notifications. Unfortunately this means that the event manager may export either one-shot or multi-shot semantics to the user. Even worse, the user has no way of knowing which semantics are being delivered. This resulted in breakage in the usb[1] library which deadlocks after notifications on its fd are disabled after the first event is delivered. This patch reworks one-shot event support to allow the user to choose whether one-shot or multi-shot semantics are desired on a per-registration basis. The event manager can then decide whether to use a one-shot or multi-shot epoll. A registration is now defined by a set of Events (as before) as well as a Lifetime (either one-shot or multi-shot). We lend monoidal structure to Lifetime choosing OneShot as the identity. This allows us to combine Lifetime/Event pairs of an fd to give the longest desired lifetime of the registration and the full set of Events for which we want notification. [1] https://github.com/basvandijk/usb/issues/7 Test Plan: Add more test cases and validate Reviewers: tibbe, AndreasVoellmy, hvr, austin Reviewed By: austin Subscribers: thomie, carter, simonmar Differential Revision: https://phabricator.haskell.org/D347
02343998