[clangd] Respect task cancellation in TUScheduler.
Summary:
- Reads are never executed if canceled before ready-to run.
In practice, we finalize cancelled reads eagerly and out-of-order.
- Cancelled reads don't prevent prior updates from being elided, as they don't
actually depend on the result of the update.
- Updates are downgraded from WantDiagnostics::Yes to WantDiagnostics::Auto when
cancelled, which allows them to be elided when all dependent reads are
cancelled and there are subsequent writes. (e.g. when the queue is backed up
with cancelled requests).
The queue operations aren't optimal (we scan the whole queue for cancelled
tasks every time the scheduler runs, and check cancellation twice in the end).
However I believe these costs are still trivial in practice (compared to any
AST operation) and the logic can be cleanly separated from the rest of the
scheduler.
Reviewers: ilya-biryukov
Subscribers: javed.absar, ioeric, MaskRay, jkorous, arphaman, kadircet, cfe-commits
Differential Revision: https://reviews.llvm.org/D54746
git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@347450 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/clangd/Cancellation.h b/clangd/Cancellation.h
index b6d6050..d6f2621 100644
--- a/clangd/Cancellation.h
+++ b/clangd/Cancellation.h
@@ -79,7 +79,7 @@
/// True if the current context is within a cancelable task which was cancelled.
/// Always false if there is no active cancelable task.
/// This isn't free (context lookup) - don't call it in a tight loop.
-bool isCancelled();
+bool isCancelled(const Context &Ctx = Context::current());
/// Conventional error when no result is returned due to cancellation.
class CancelledError : public llvm::ErrorInfo<CancelledError> {
