clang-tools-extra/clangd/support/Cancellation.cpp

   1 //===--- Cancellation.cpp -----------------------------------------*-C++-*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "support/Cancellation.h"
  10 #include <atomic>
  11
  12 namespace clang {
  13 namespace clangd {
  14
  15 char CancelledError::ID = 0;
  16
  17 // We don't want a cancelable scope to "shadow" an enclosing one.
  18 struct CancelState {
  19   std::shared_ptr<std::atomic<int>> Cancelled;
  20   const CancelState *Parent;
  21 };
  22 static Key<CancelState> StateKey;
  23
  24 std::pair<Context, Canceler> cancelableTask(int Reason) {
  25   assert(Reason != 0 && "Can't detect cancellation if Reason is zero");
  26   CancelState State;
  27   State.Cancelled = std::make_shared<std::atomic<int>>();
  28   State.Parent = Context::current().get(StateKey);
  29   return {
  30       Context::current().derive(StateKey, State),
  31       [Reason, Flag(State.Cancelled)] { *Flag = Reason; },
  32   };
  33 }
  34
  35 int isCancelled(const Context &Ctx) {
  36   for (const CancelState *State = Ctx.get(StateKey); State != nullptr;
  37        State = State->Parent)
  38     if (int Reason = State->Cancelled->load())
  39       return Reason;
  40   return 0;
  41 }
  42
  43 } // namespace clangd
  44 } // namespace clang