/*
 *  Copyright 2014 The WebRTC Project Authors. All rights reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include "rtc_base/deprecated/recursive_critical_section.h"

#include <atomic>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <set>
#include <utility>
#include <vector>

#include "api/units/time_delta.h"
#include "rtc_base/checks.h"
#include "rtc_base/event.h"
#include "rtc_base/platform_thread.h"
#include "rtc_base/thread.h"
#include "rtc_base/thread_annotations.h"
#include "test/gtest.h"

namespace webrtc {

namespace {

constexpr TimeDelta kLongTime = TimeDelta::Seconds(10);
constexpr int kNumThreads = 16;
constexpr int kOperationsToRun = 1000;

class UniqueValueVerifier {
 public:
  void Verify(const std::vector<int>& values) {
    for (size_t i = 0; i < values.size(); ++i) {
      std::pair<std::set<int>::iterator, bool> result =
          all_values_.insert(values[i]);
      // Each value should only be taken by one thread, so if this value
      // has already been added, something went wrong.
      EXPECT_TRUE(result.second)
          << " Thread=" << Thread::Current() << " value=" << values[i];
    }
  }

  void Finalize() {}

 private:
  std::set<int> all_values_;
};

class CompareAndSwapVerifier {
 public:
  CompareAndSwapVerifier() : zero_count_(0) {}

  void Verify(const std::vector<int>& values) {
    for (auto v : values) {
      if (v == 0) {
        EXPECT_EQ(0, zero_count_) << "Thread=" << Thread::Current();
        ++zero_count_;
      } else {
        EXPECT_EQ(1, v) << " Thread=" << Thread::Current();
      }
    }
  }

  void Finalize() { EXPECT_EQ(1, zero_count_); }

 private:
  int zero_count_;
};

class RunnerBase {
 public:
  explicit RunnerBase(int value)
      : threads_active_(0),
        start_event_(true, false),
        done_event_(true, false),
        shared_value_(value) {}

  bool Run() {
    // Signal all threads to start.
    start_event_.Set();

    // Wait for all threads to finish.
    return done_event_.Wait(kLongTime);
  }

  void SetExpectedThreadCount(int count) { threads_active_.store(count); }

  int shared_value() const { return shared_value_; }

 protected:
  void BeforeStart() { ASSERT_TRUE(start_event_.Wait(kLongTime)); }

  // Returns true if all threads have finished.
  bool AfterEnd() {
    if (threads_active_.fetch_sub(1) == 1) {
      done_event_.Set();
      return true;
    }
    return false;
  }

  std::atomic<int> threads_active_;
  Event start_event_;
  Event done_event_;
  int shared_value_;
};

class RTC_LOCKABLE CriticalSectionLock {
 public:
  void Lock() RTC_EXCLUSIVE_LOCK_FUNCTION() { cs_.Enter(); }
  void Unlock() RTC_UNLOCK_FUNCTION() { cs_.Leave(); }

 private:
  RecursiveCriticalSection cs_;
};

template <class Lock>
class LockRunner : public RunnerBase {
 public:
  LockRunner() : RunnerBase(0) {}

  void Loop() {
    BeforeStart();

    lock_.Lock();

    EXPECT_EQ(0, shared_value_);
    int old = shared_value_;

    // Use a loop to increase the chance of race.
    for (int i = 0; i < kOperationsToRun; ++i) {
      ++shared_value_;
    }
    EXPECT_EQ(old + kOperationsToRun, shared_value_);
    shared_value_ = 0;

    lock_.Unlock();

    AfterEnd();
  }

 private:
  Lock lock_;
};

template <typename Runner>
void StartThreads(std::vector<std::unique_ptr<Thread>>* threads,
                  Runner* handler) {
  for (int i = 0; i < kNumThreads; ++i) {
    std::unique_ptr<Thread> thread(Thread::Create());
    thread->Start();
    thread->PostTask([handler] { handler->Loop(); });
    threads->push_back(std::move(thread));
  }
}

}  // namespace

TEST(RecursiveCriticalSectionTest, Basic) {
  // Create and start lots of threads.
  LockRunner<CriticalSectionLock> runner;
  std::vector<std::unique_ptr<Thread>> threads;
  StartThreads(&threads, &runner);
  runner.SetExpectedThreadCount(kNumThreads);

  // Release the hounds!
  EXPECT_TRUE(runner.Run());
  EXPECT_EQ(0, runner.shared_value());
}

class PerfTestData {
 public:
  PerfTestData(int expected_count, Event* event)
      : cache_line_barrier_1_(),
        cache_line_barrier_2_(),
        expected_count_(expected_count),
        event_(event) {
    cache_line_barrier_1_[0]++;  // Avoid 'is not used'.
    cache_line_barrier_2_[0]++;  // Avoid 'is not used'.
  }
  ~PerfTestData() {}

  void AddToCounter(int add) {
    CritScope cs(&lock_);
    my_counter_ += add;
    if (my_counter_ == expected_count_)
      event_->Set();
  }

  int64_t total() const {
    // Assume that only one thread is running now.
    return my_counter_;
  }

 private:
  uint8_t cache_line_barrier_1_[64];
  RecursiveCriticalSection lock_;
  uint8_t cache_line_barrier_2_[64];
  int64_t my_counter_ = 0;
  const int expected_count_;
  Event* const event_;
};

class PerfTestThread {
 public:
  void Start(PerfTestData* data, int repeats, int id) {
    RTC_DCHECK(!data_);
    data_ = data;
    repeats_ = repeats;
    my_id_ = id;
    thread_ = PlatformThread::SpawnJoinable(
        [this] {
          for (int i = 0; i < repeats_; ++i)
            data_->AddToCounter(my_id_);
        },
        "CsPerf");
  }

  void Stop() {
    RTC_DCHECK(data_);
    thread_.Finalize();
    repeats_ = 0;
    data_ = nullptr;
    my_id_ = 0;
  }

 private:
  PlatformThread thread_;
  PerfTestData* data_ = nullptr;
  int repeats_ = 0;
  int my_id_ = 0;
};

// Comparison of output of this test as tested on a MacBook Pro, 13-inch,
// 2017, 3,5 GHz Intel Core i7, 16 GB 2133 MHz LPDDR3,
// running macOS Mojave, 10.14.3.
//
// Native mutex implementation using fair policy (previously macOS default):
// Approximate CPU usage:
// real    4m54.612s
// user    1m20.575s
// sys     3m48.872s
// Unit test output:
// [       OK ] RecursiveCriticalSectionTest.Performance (294375 ms)
//
// Native mutex implementation using first fit policy (current macOS default):
// Approximate CPU usage:
// real    0m11.535s
// user    0m12.738s
// sys     0m31.207s
// Unit test output:
// [       OK ] RecursiveCriticalSectionTest.Performance (11444 ms)
//
// Special partially spin lock based implementation:
// Approximate CPU usage:
// real    0m2.113s
// user    0m3.014s
// sys     0m4.495s
// Unit test output:
// [       OK ] RecursiveCriticalSectionTest.Performance (1885 ms)
//
// The test is disabled by default to avoid unecessarily loading the bots.
TEST(RecursiveCriticalSectionTest, DISABLED_Performance) {
  PerfTestThread threads[8];
  Event event;

  static const int kThreadRepeats = 10000000;
  static const int kExpectedCount = kThreadRepeats * std::ssize(threads);
  PerfTestData test_data(kExpectedCount, &event);

  for (auto& t : threads)
    t.Start(&test_data, kThreadRepeats, 1);

  event.Wait(Event::kForever);

  for (auto& t : threads)
    t.Stop();
}

}  // namespace webrtc