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       1             : //===--- ThreadPool.h --------------------------------------------*- C++-*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : 
      10             : #ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_THREADING_H
      11             : #define LLVM_CLANG_TOOLS_EXTRA_CLANGD_THREADING_H
      12             : 
      13             : #include "Context.h"
      14             : #include "Function.h"
      15             : #include "llvm/ADT/Twine.h"
      16             : #include <cassert>
      17             : #include <condition_variable>
      18             : #include <memory>
      19             : #include <mutex>
      20             : #include <vector>
      21             : 
      22             : namespace clang {
      23             : namespace clangd {
      24             : 
      25             : /// A threadsafe flag that is initially clear.
      26           0 : class Notification {
      27             : public:
      28             :   // Sets the flag. No-op if already set.
      29             :   void notify();
      30             :   // Blocks until flag is set.
      31             :   void wait() const;
      32             : 
      33             : private:
      34             :   bool Notified = false;
      35             :   mutable std::condition_variable CV;
      36             :   mutable std::mutex Mu;
      37             : };
      38             : 
      39             : /// Limits the number of threads that can acquire the lock at the same time.
      40             : class Semaphore {
      41             : public:
      42             :   Semaphore(std::size_t MaxLocks);
      43             : 
      44             :   void lock();
      45             :   void unlock();
      46             : 
      47             : private:
      48             :   std::mutex Mutex;
      49             :   std::condition_variable SlotsChanged;
      50             :   std::size_t FreeSlots;
      51             : };
      52             : 
      53             : /// A point in time we can wait for.
      54             : /// Can be zero (don't wait) or infinity (wait forever).
      55             : /// (Not time_point::max(), because many std::chrono implementations overflow).
      56             : class Deadline {
      57             : public:
      58             :   Deadline(std::chrono::steady_clock::time_point Time)
      59             :       : Type(Finite), Time(Time) {}
      60             :   static Deadline zero() { return Deadline(Zero); }
      61             :   static Deadline infinity() { return Deadline(Infinite); }
      62             : 
      63             :   std::chrono::steady_clock::time_point time() const {
      64             :     assert(Type == Finite);
      65             :     return Time;
      66             :   }
      67             :   bool expired() const {
      68             :     return (Type == Zero) ||
      69             :            (Type == Finite && Time < std::chrono::steady_clock::now());
      70             :   }
      71             :   bool operator==(const Deadline &Other) const {
      72             :     return (Type == Other.Type) && (Type != Finite || Time == Other.Time);
      73             :   }
      74             : 
      75             : private:
      76             :   enum Type { Zero, Infinite, Finite };
      77             : 
      78             :   Deadline(enum Type Type) : Type(Type) {}
      79             :   enum Type Type;
      80             :   std::chrono::steady_clock::time_point Time;
      81             : };
      82             : 
      83             : /// Makes a deadline from a timeout in seconds. None means wait forever.
      84             : Deadline timeoutSeconds(llvm::Optional<double> Seconds);
      85             : /// Wait once on CV for the specified duration.
      86             : void wait(std::unique_lock<std::mutex> &Lock, std::condition_variable &CV,
      87             :           Deadline D);
      88             : /// Waits on a condition variable until F() is true or D expires.
      89             : template <typename Func>
      90             : LLVM_NODISCARD bool wait(std::unique_lock<std::mutex> &Lock,
      91             :                          std::condition_variable &CV, Deadline D, Func F) {
      92             :   while (!F()) {
      93             :     if (D.expired())
      94             :       return false;
      95             :     wait(Lock, CV, D);
      96             :   }
      97             :   return true;
      98             : }
      99             : 
     100             : /// Runs tasks on separate (detached) threads and wait for all tasks to finish.
     101             : /// Objects that need to spawn threads can own an AsyncTaskRunner to ensure they
     102             : /// all complete on destruction.
     103           0 : class AsyncTaskRunner {
     104             : public:
     105             :   /// Destructor waits for all pending tasks to finish.
     106             :   ~AsyncTaskRunner();
     107             : 
     108           0 :   void wait() const { (void)wait(Deadline::infinity()); }
     109             :   LLVM_NODISCARD bool wait(Deadline D) const;
     110             :   // The name is used for tracing and debugging (e.g. to name a spawned thread).
     111             :   void runAsync(const llvm::Twine &Name, llvm::unique_function<void()> Action);
     112             : 
     113             : private:
     114             :   mutable std::mutex Mutex;
     115             :   mutable std::condition_variable TasksReachedZero;
     116             :   std::size_t InFlightTasks = 0;
     117             : };
     118             : } // namespace clangd
     119             : } // namespace clang
     120             : #endif