Improve shutdown behavior (enable clean shutdowns) #232
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added 2 commits
January 1, 2023 20:36
This commit is the first in a small series to improve the shutdown
behavior of xlxd.
(1) Ensures worker threads block signals by masking all signals prior
to the main reflector startup via CReflector::Start().
(2) Uses sigwaitinfo() in the main thread to wait on a few normal
termination signals. This works for both daemon and non-daemon
operation.
Second patch in the improve-shutdown series. This replaces blocking
sleeps with the use of condition variables for signaling thread
shutdown. The details are:
(1) Create CSimpleCondition class to provide a very basic (simple)
condition variable that can be used in situations where external
mutex control is not required, i.e., the class contains both a
managed mutex and condition variable. Instances of this class
can be used for basic signaling, and waiters can specify user
defined predicates.
(2) Replace instances of large sleeps in worker threads with use of
CSimpleCondition. This allows for very quick response times from
worker threads when a shutdown has been initiated.
(3) Change stop thread booleans to atomic_bool.
(4) Fixes small whitespace discprencies.
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The two commits in this PR have their own commentary describing the changes that can be referred to, but to quickly summarize, this PR enables clean shutdowns of the reflector. The current code has no way of performing a clean shutdown for a couple reasons: (1) infinite loops in main() and (2) long blocking sleeps in various worker threads.
The general approach was to swap the blocking sleeps with condition variables that are signaled during shutdown, and to add signal handling in the main thread for termination signals. With these changes the reflector shuts down cleanly in less than a second with run as a daemon or in the foreground (when in the foreground, CTRL-C will initiate the shutdown).