// Copyright (c) 2014 Baidu, Inc.G
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Authors: Lei He (helei@qiyi.com)

#ifndef BRPC_POLICY_AUTO_CONCURRENCY_LIMITER_H
#define BRPC_POLICY_AUTO_CONCURRENCY_LIMITER_H

#include "bvar/bvar.h"
#include "butil/containers/bounded_queue.h"
#include "brpc/concurrency_limiter.h"

namespace brpc {
namespace policy {

class AutoConcurrencyLimiter : public ConcurrencyLimiter {
public:
    AutoConcurrencyLimiter();

    bool OnRequested(int current_concurrency) override;
    
    void OnResponded(int error_code, int64_t latency_us) override;

    int MaxConcurrency() override;

    AutoConcurrencyLimiter* New(const AdaptiveMaxConcurrency&) const override;

private:
    struct SampleWindow {
        SampleWindow() 
            : start_time_us(0)
            , succ_count(0)
            , failed_count(0)
            , total_failed_us(0)
            , total_succ_us(0) {}
        int64_t start_time_us;
        int32_t succ_count;
        int32_t failed_count;
        int64_t total_failed_us;
        int64_t total_succ_us;
    };

    bool AddSample(int error_code, int64_t latency_us, int64_t sampling_time_us);
    int64_t NextResetTime(int64_t sampling_time_us);

    // The following methods are not thread safe and can only be called 
    // in AppSample()
    void UpdateMaxConcurrency(int64_t sampling_time_us);
    void ResetSampleWindow(int64_t sampling_time_us);
    void UpdateMinLatency(int64_t latency_us);
    void UpdateQps(double qps);

    // modified per sample-window or more
    int _max_concurrency;
    int64_t _remeasure_start_us;
    int64_t _reset_latency_us;
    int64_t _min_latency_us; 
    double _ema_max_qps;
    double _explore_ratio;
  
    // modified per sample.
    butil::atomic<int64_t> BAIDU_CACHELINE_ALIGNMENT _last_sampling_time_us;
    butil::Mutex _sw_mutex;
    SampleWindow _sw;

    // modified per request.
    butil::atomic<int32_t> BAIDU_CACHELINE_ALIGNMENT _total_succ_req;
};

}  // namespace policy
}  // namespace brpc


#endif // BRPC_POLICY_AUTO_CONCURRENCY_LIMITER_H
