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//===--- ThreadPool.h --------------------------------------------*- C++-*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
#include "Context.h"
#include "Function.h"
#include "llvm/ADT/Twine.h"
#include <cassert>
#include <condition_variable>
#include <memory>
#include <mutex>
#include <vector>
namespace clang {
namespace clangd {
/// A threadsafe flag that is initially clear.
class Notification {
// Sets the flag. No-op if already set.
void notify();
// Blocks until flag is set.
void wait() const;
bool Notified = false;
mutable std::condition_variable CV;
mutable std::mutex Mu;
/// Limits the number of threads that can acquire the lock at the same time.
class Semaphore {
Semaphore(std::size_t MaxLocks);
void lock();
void unlock();
std::mutex Mutex;
std::condition_variable SlotsChanged;
std::size_t FreeSlots;
/// A point in time we can wait for.
/// Can be zero (don't wait) or infinity (wait forever).
/// (Not time_point::max(), because many std::chrono implementations overflow).
class Deadline {
Deadline(std::chrono::steady_clock::time_point Time)
: Type(Finite), Time(Time) {}
static Deadline zero() { return Deadline(Zero); }
static Deadline infinity() { return Deadline(Infinite); }
std::chrono::steady_clock::time_point time() const {
assert(Type == Finite);
return Time;
bool expired() const {
return (Type == Zero) ||
(Type == Finite && Time < std::chrono::steady_clock::now());
bool operator==(const Deadline &Other) const {
return (Type == Other.Type) && (Type != Finite || Time == Other.Time);
enum Type { Zero, Infinite, Finite };
Deadline(enum Type Type) : Type(Type) {}
enum Type Type;
std::chrono::steady_clock::time_point Time;
/// Makes a deadline from a timeout in seconds. None means wait forever.
Deadline timeoutSeconds(llvm::Optional<double> Seconds);
/// Wait once on CV for the specified duration.
void wait(std::unique_lock<std::mutex> &Lock, std::condition_variable &CV,
Deadline D);
/// Waits on a condition variable until F() is true or D expires.
template <typename Func>
LLVM_NODISCARD bool wait(std::unique_lock<std::mutex> &Lock,
std::condition_variable &CV, Deadline D, Func F) {
while (!F()) {
if (D.expired())
return false;
wait(Lock, CV, D);
return true;
/// Runs tasks on separate (detached) threads and wait for all tasks to finish.
/// Objects that need to spawn threads can own an AsyncTaskRunner to ensure they
/// all complete on destruction.
class AsyncTaskRunner {
/// Destructor waits for all pending tasks to finish.
void wait() const { (void)wait(Deadline::infinity()); }
LLVM_NODISCARD bool wait(Deadline D) const;
// The name is used for tracing and debugging (e.g. to name a spawned thread).
void runAsync(const llvm::Twine &Name, llvm::unique_function<void()> Action);
mutable std::mutex Mutex;
mutable std::condition_variable TasksReachedZero;
std::size_t InFlightTasks = 0;
} // namespace clangd
} // namespace clang