//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  This source code is licensed under both the GPLv2 (found in the

//  COPYING file in the root directory) and Apache 2.0 License

//  (found in the LICENSE.Apache file in the root directory).

#include "db/flush_scheduler.h"

#include <cassert>

#include "db/column_family.h"

namespace ROCKSDB_NAMESPACE {

void FlushScheduler::ScheduleWork(ColumnFamilyData* cfd) {

#ifndef NDEBUG

  {

    std::lock_guard<std::mutex> lock(checking_mutex_);

    assert(checking_set_.count(cfd) == 0);

    checking_set_.insert(cfd);

  }

#endif  // NDEBUG

  cfd->Ref();

// Suppress false positive clang analyzer warnings.

#ifndef __clang_analyzer__

  Node* node = new Node{cfd, head_.load(std::memory_order_relaxed)};

  while (!head_.compare_exchange_strong(

      node->next, node, std::memory_order_relaxed, std::memory_order_relaxed)) {

    // failing CAS updates the first param, so we are already set for

    // retry.  TakeNextColumnFamily won't happen until after another

    // inter-thread synchronization, so we don't even need release

    // semantics for this CAS

  }

#endif  // __clang_analyzer__

}

ColumnFamilyData* FlushScheduler::TakeNextColumnFamily() {

  while (true) {

    if (head_.load(std::memory_order_relaxed) == nullptr) {

      return nullptr;

    }

    // dequeue the head

    Node* node = head_.load(std::memory_order_relaxed);

    head_.store(node->next, std::memory_order_relaxed);

    ColumnFamilyData* cfd = node->column_family;

    delete node;

#ifndef NDEBUG

    {

      std::lock_guard<std::mutex> lock(checking_mutex_);

      auto iter = checking_set_.find(cfd);

      assert(iter != checking_set_.end());

      checking_set_.erase(iter);

    }

#endif  // NDEBUG

    if (!cfd->IsDropped()) {

      // success

      return cfd;

    }

    // no longer relevant, retry

    cfd->UnrefAndTryDelete();

  }

}

bool FlushScheduler::Empty() {

  auto rv = head_.load(std::memory_order_relaxed) == nullptr;

#ifndef NDEBUG

  std::lock_guard<std::mutex> lock(checking_mutex_);

  // Empty is allowed to be called concurrnetly with ScheduleFlush. It would

  // only miss the recent schedules.

  assert((rv == checking_set_.empty()) || rv);

#endif  // NDEBUG

  return rv;

}

void FlushScheduler::Clear() {

  ColumnFamilyData* cfd;

  while ((cfd = TakeNextColumnFamily()) != nullptr) {

    cfd->UnrefAndTryDelete();

  }

  assert(head_.load(std::memory_order_relaxed) == nullptr);

}

}  // namespace ROCKSDB_NAMESPACE