llvm-project

930f6468 - [lldb] Implement coalescing of disjoint progress events (#84854)

[lldb] Implement coalescing of disjoint progress events (#84854) This implements coalescing of progress events using a timeout, as discussed in the RFC on Discourse [1]. This PR consists of two commits which, depending on the feedback, I may split up into two PRs. For now, I think it's easier to review this as a whole. 1. The first commit introduces a new generic `Alarm` class. The class lets you to schedule a function (callback) to be executed after a given timeout expires. You can cancel and reset a callback before its corresponding timeout expires. It achieves this with the help of a worker thread that sleeps until the next timeout expires. The only guarantee it provides is that your function is called no sooner than the requested timeout. Because the callback is called directly from the worker thread, a long running callback could potentially block the worker thread. I intentionally kept the implementation as simple as possible while addressing the needs for the `ProgressManager` use case. If we want to rely on this somewhere else, we can reassess whether we need to address those limitations. 2. The second commit uses the Alarm class to coalesce progress events. To recap the Discourse discussion, when multiple progress events with the same title execute in close succession, they get broadcast as one to `eBroadcastBitProgressCategory`. The `ProgressManager` keeps track of the in-flight progress events and when the refcount hits zero, the Alarm class is used to schedule broadcasting the event. If a new progress event comes in before the alarm fires, the alarm is reset (and the process repeats when the new progress event ends). If no new event comes in before the timeout expires, the progress event is broadcast. [1] https://discourse.llvm.org/t/rfc-improve-lldb-progress-reporting/75717/