[Lldb-commits] [PATCH] D13727: Add task pool to LLDB

Zachary Turner via lldb-commits lldb-commits at lists.llvm.org
Wed Oct 14 12:01:39 PDT 2015

zturner added a comment.

The only real suggestion / question I have is a design one.

By using this implementation we can't take advantage of the system thread pool.  That was the point of using std async in the first place, but we found that it doesn't always limit the number of threads.  Maybe there's a way to get the best of both worlds.

What if, instead of storing a `std::queue<std::function<void()>>` you instead store a `std::queue<std::packaged_task>`.  Now the only problem that remains is how to guarantee that no more than `std::hardware_concurrency()` of these `packaged_task` is waiting at any given time.  You could do this by taking the `std::function` that someone gives you, and wrapping it in a `packaged_task` which first runs the function, and then signals a condition variable after the function completes.  Then a single "dispatch" thread (for lack of a better word) could wake on this condition variable, pull a new `packaged_task` off the queue, and execute it asynchronously.  You'd also need to signal that same condition variable when a new item is added to the queue so that the dispatch thread could decide whether to run it immediately (if it's under-scheduled) or wait if it's full.

This would probably also make the implementation quite a bit simpler as well as being able to take advantage of any deep optimizations a platform has in its own thread pool implementation (if any).


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