tree f1a54c6fe2871203ca5fd2ba837bfb9e89fa158f
parent 152893c4f17da93c2f7d6a672506272956cfab8a
author Carl Lerche <me@carllerche.com> 1536182485 -0700
committer GitHub <noreply@github.com> 1536182485 -0700
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Reduce spurious awaken calls (#875)

When a registration is signalled from a side thread and the main thread
is blocke in `poll`, a pipe is used to interrupt the blocked `poll`
call. However, this pipe write is expensive and should only be made when
`poll` is blocked.

To avoid spurrious calls, the readiness queue tracks a `sleep_token`.
When a node is scheduled, it checks if the `sleep_token` is present. If
it is, it writes to the pipe to wake up the main thread.

Currently, the `sleep_token` isn't cleared when the blocking call to
`poll` wakes up naturally. This results in the next registration signal
to write to the pipe even though the main thread is not blocked.

This patch clears the `sleep_token` when the blocking call returns.

Fixes #785