Improve config sync locking (support/2.12) #8511
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This avoid having to pass a lock implictly using the captured variables of a lambda.
Merge AsyncTryActivateZonesStage and TryActivateZonesStageCallback and name the result TryActivateZonesStage. The old split was a leftover from the one being a callback function with no actual meaningful separation.
No longer needed as its only user now uses std::mutex.
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This pull request greatly simplifies the locking during an incoming config sync and removes a spin lock that got introduced as a workaround.
History
#7230 recognized the need that the incoming config sync must not happen concurrently and added a mutex. #7936 then fixed a shortcoming that the mutex was not hold during the complete sync and reload process by using a
icinga::Shared<boost::mutex::scoped_lock>which is passed to a callback function by capturing it in a lambda and therefore the unlock operations runs when the callback is destroyed. Unfortunately, bothstd::mutexandboost::mutexhave undefined behavior when the unlock operation happens in a different thread than the lock operation, which is a problem as the callback can run on any other worker thread. As a workaround, #8364 introduced a spin lock, that does not have undefined behavior in this case.Changes
With this pull request, the config sync and subsequent reload no longer post a callback to a worker thread but instead just waits for the process to finish while simply holding the lock without any shared pointer magic. To do so, a new method
WaitForResult()is added toicinga::Processwhich allows to block until the process has finished.fixes #8336
fixes #8507
backport of #8488