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// Copyright (c) 2015 Baidu, Inc.
//
// 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.
// Author: Zhangyi Chen (chenzhangyi01@baidu.com)
// Date: 2015/09/15 15:14:32
#include "bvar/detail/percentile.h"
#include "butil/logging.h"
namespace bvar {
namespace detail {
inline uint32_t ones32(uint32_t x) {
/* 32-bit recursive reduction using SWAR...
* but first step is mapping 2-bit values
* into sum of 2 1-bit values in sneaky way
*/
x -= ((x >> 1) & 0x55555555);
x = (((x >> 2) & 0x33333333) + (x & 0x33333333));
x = (((x >> 4) + x) & 0x0f0f0f0f);
x += (x >> 8);
x += (x >> 16);
return (x & 0x0000003f);
}
inline uint32_t log2(uint32_t x) {
int y = (x & (x - 1));
y |= -y;
y >>= 31;
x |= (x >> 1);
x |= (x >> 2);
x |= (x >> 4);
x |= (x >> 8);
x |= (x >> 16);
return(ones32(x) - 1 - y);
}
inline size_t get_interval_index(int64_t &x) {
if (x <= 2) {
return 0;
} else if (x > std::numeric_limits<uint32_t>::max()) {
x = std::numeric_limits<uint32_t>::max();
return 31;
} else {
return log2(x) - 1;
}
}
class AddLatency {
public:
AddLatency(int64_t latency) : _latency(latency) {}
void operator()(GlobalValue<Percentile::combiner_type>& global_value,
ThreadLocalPercentileSamples& local_value) const {
// Copy to latency since get_interval_index may change input.
int64_t latency = _latency;
const size_t index = get_interval_index(latency);
PercentileInterval<ThreadLocalPercentileSamples::SAMPLE_SIZE>&
interval = local_value.get_interval_at(index);
if (interval.full()) {
GlobalPercentileSamples* g = global_value.lock();
g->get_interval_at(index).merge(interval);
g->_num_added += interval.added_count();
global_value.unlock();
local_value._num_added -= interval.added_count();
interval.clear();
}
interval.add64(latency);
++local_value._num_added;
}
private:
int64_t _latency;
};
Percentile::Percentile() : _combiner(NULL), _sampler(NULL) {
_combiner = new combiner_type;
}
Percentile::~Percentile() {
// Have to destroy sampler first to avoid the race between destruction and
// sampler
if (_sampler != NULL) {
_sampler->destroy();
_sampler = NULL;
}
delete _combiner;
}
Percentile::value_type Percentile::reset() {
return _combiner->reset_all_agents();
}
Percentile::value_type Percentile::get_value() const {
return _combiner->combine_agents();
}
Percentile &Percentile::operator<<(int64_t latency) {
agent_type* agent = _combiner->get_or_create_tls_agent();
if (BAIDU_UNLIKELY(!agent)) {
LOG(FATAL) << "Fail to create agent";
return *this;
}
if (latency < 0) {
// we don't check overflow(of uint32) in percentile because the
// overflowed value which is included in last range does not affect
// overall distribution of other values too much.
if (!_debug_name.empty()) {
LOG(WARNING) << "Input=" << latency << " to `" << _debug_name
<< "' is negative, drop";
} else {
LOG(WARNING) << "Input=" << latency << " to Percentile("
<< (void*)this << ") is negative, drop";
}
return *this;
}
agent->merge_global(AddLatency(latency));
return *this;
}
} // namespace detail
} // namespace bvar