rocksdb/db/write_controller.h

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#pragma once
#include <stdint.h>
#include <memory>
namespace rocksdb {
class WriteControllerToken;
// WriteController is controlling write stalls in our write code-path. Write
// stalls happen when compaction can't keep up with write rate.
// All of the methods here (including WriteControllerToken's destructors) need
// to be called while holding DB mutex
class WriteController {
public:
WriteController() : total_stopped_(0), total_delay_us_(0) {}
~WriteController() = default;
// When an actor (column family) requests a stop token, all writes will be
// stopped until the stop token is released (deleted)
std::unique_ptr<WriteControllerToken> GetStopToken();
// When an actor (column family) requests a delay token, total delay for all
// writes will be increased by delay_us. The delay will last until delay token
// is released
std::unique_ptr<WriteControllerToken> GetDelayToken(uint64_t delay_us);
// these two metods are querying the state of the WriteController
bool IsStopped() const;
uint64_t GetDelay() const;
private:
friend class WriteControllerToken;
friend class StopWriteToken;
friend class DelayWriteToken;
int total_stopped_;
uint64_t total_delay_us_;
};
class WriteControllerToken {
public:
explicit WriteControllerToken(WriteController* controller)
: controller_(controller) {}
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virtual ~WriteControllerToken() {}
protected:
WriteController* controller_;
private:
// no copying allowed
WriteControllerToken(const WriteControllerToken&) = delete;
void operator=(const WriteControllerToken&) = delete;
};
class StopWriteToken : public WriteControllerToken {
public:
explicit StopWriteToken(WriteController* controller)
: WriteControllerToken(controller) {}
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virtual ~StopWriteToken();
};
class DelayWriteToken : public WriteControllerToken {
public:
DelayWriteToken(WriteController* controller, uint64_t delay_us)
: WriteControllerToken(controller), delay_us_(delay_us) {}
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virtual ~DelayWriteToken();
private:
uint64_t delay_us_;
};
} // namespace rocksdb