152 lines · cpp
1//===-- BackgroundQueue.cpp - Task queue for background index -------------===//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-exception6//7//===----------------------------------------------------------------------===//8 9#include "index/Background.h"10#include "support/Logger.h"11#include <optional>12 13namespace clang {14namespace clangd {15 16static std::atomic<bool> PreventStarvation = {false};17 18void BackgroundQueue::preventThreadStarvationInTests() {19 PreventStarvation.store(true);20}21 22void BackgroundQueue::work(std::function<void()> OnIdle) {23 while (true) {24 std::optional<Task> Task;25 {26 std::unique_lock<std::mutex> Lock(Mu);27 CV.wait(Lock, [&] { return ShouldStop || !Queue.empty(); });28 if (ShouldStop) {29 Queue.clear();30 CV.notify_all();31 return;32 }33 ++Stat.Active;34 std::pop_heap(Queue.begin(), Queue.end());35 Task = std::move(Queue.back());36 Queue.pop_back();37 notifyProgress();38 }39 40 if (Task->ThreadPri != llvm::ThreadPriority::Default &&41 !PreventStarvation.load())42 llvm::set_thread_priority(Task->ThreadPri);43 Task->Run();44 if (Task->ThreadPri != llvm::ThreadPriority::Default)45 llvm::set_thread_priority(llvm::ThreadPriority::Default);46 47 {48 std::unique_lock<std::mutex> Lock(Mu);49 ++Stat.Completed;50 if (Stat.Active == 1 && Queue.empty()) {51 // We just finished the last item, the queue is going idle.52 assert(ShouldStop || Stat.Completed == Stat.Enqueued);53 Stat.LastIdle = Stat.Completed;54 if (OnIdle) {55 Lock.unlock();56 OnIdle();57 Lock.lock();58 }59 }60 assert(Stat.Active > 0 && "before decrementing");61 --Stat.Active;62 notifyProgress();63 }64 CV.notify_all();65 }66}67 68void BackgroundQueue::stop() {69 {70 std::lock_guard<std::mutex> QueueLock(Mu);71 ShouldStop = true;72 }73 CV.notify_all();74}75 76// Tweaks the priority of a newly-enqueued task, or returns false to cancel it.77bool BackgroundQueue::adjust(Task &T) {78 // It is tempting to drop duplicates of queued tasks, and merely deprioritize79 // duplicates of completed tasks (i.e. reindexing on CDB changes). But:80 // - the background indexer doesn't support reindexing well, e.g. staleness81 // is checked at *enqueue* time only, and doesn't account for compile flags82 // - reindexing on compile flags is often a poor use of CPU in practice83 if (T.Key && !SeenKeys.insert(T.Key).second)84 return false;85 T.QueuePri = std::max(T.QueuePri, Boosts.lookup(T.Tag));86 return true;87}88 89void BackgroundQueue::push(Task T) {90 {91 std::lock_guard<std::mutex> Lock(Mu);92 if (!adjust(T))93 return;94 Queue.push_back(std::move(T));95 std::push_heap(Queue.begin(), Queue.end());96 ++Stat.Enqueued;97 notifyProgress();98 }99 CV.notify_all();100}101 102void BackgroundQueue::append(std::vector<Task> Tasks) {103 {104 std::lock_guard<std::mutex> Lock(Mu);105 for (Task &T : Tasks) {106 if (!adjust(T))107 continue;108 Queue.push_back(std::move(T));109 ++Stat.Enqueued;110 }111 std::make_heap(Queue.begin(), Queue.end());112 notifyProgress();113 }114 CV.notify_all();115}116 117void BackgroundQueue::boost(llvm::StringRef Tag, unsigned NewPriority) {118 std::lock_guard<std::mutex> Lock(Mu);119 unsigned &Boost = Boosts[Tag];120 bool Increase = NewPriority > Boost;121 Boost = NewPriority;122 if (!Increase)123 return; // existing tasks unaffected124 125 unsigned Changes = 0;126 for (Task &T : Queue)127 if (Tag == T.Tag && NewPriority > T.QueuePri) {128 T.QueuePri = NewPriority;129 ++Changes;130 }131 if (Changes)132 std::make_heap(Queue.begin(), Queue.end());133 // No need to signal, only rearranged items in the queue.134}135 136bool BackgroundQueue::blockUntilIdleForTest(137 std::optional<double> TimeoutSeconds) {138 std::unique_lock<std::mutex> Lock(Mu);139 return wait(Lock, CV, timeoutSeconds(TimeoutSeconds),140 [&] { return Queue.empty() && Stat.Active == 0; });141}142 143void BackgroundQueue::notifyProgress() const {144 dlog("Queue: {0}/{1} ({2} active). Last idle at {3}", Stat.Completed,145 Stat.Enqueued, Stat.Active, Stat.LastIdle);146 if (OnProgress)147 OnProgress(Stat);148}149 150} // namespace clangd151} // namespace clang152