foundationdb/flow/Histogram.h

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/*
* Histogram.h
*
* This source file is part of the FoundationDB open source project
*
* Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
*
* 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.
*/
#ifndef FLOW_HISTOGRAM_H
#define FLOW_HISTOGRAM_H
#pragma once
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#include <flow/Arena.h>
#include <string>
#include <map>
#include <unordered_map>
#ifdef _WIN32
#include <intrin.h>
#pragma intrinsic(_BitScanReverse)
#endif
class Histogram;
class HistogramRegistry {
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public:
void registerHistogram(Histogram* h);
void unregisterHistogram(Histogram* h);
Histogram* lookupHistogram(std::string name);
void logReport();
private:
// This map is ordered by key so that ops within the same group end up
// next to each other in the trace log.
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std::map<std::string, Histogram*> histograms;
};
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HistogramRegistry& GetHistogramRegistry();
/*
* A fast histogram with power-of-two spaced buckets.
*
* For more information about this technique, see:
* https://www.fsl.cs.stonybrook.edu/project-osprof.html
*/
class Histogram sealed : public ReferenceCounted<Histogram> {
public:
enum class Unit { microseconds, bytes, bytes_per_second };
private:
static const std::unordered_map<Unit, std::string> UnitToStringMapper;
Histogram(std::string group, std::string op, Unit unit, HistogramRegistry& registry)
: group(group), op(op), unit(unit), registry(registry), ReferenceCounted<Histogram>() {
ASSERT(UnitToStringMapper.find(unit) != UnitToStringMapper.end());
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clear();
}
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static std::string generateName(std::string group, std::string op) { return group + ":" + op; }
public:
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~Histogram() { registry.unregisterHistogram(this); }
static Reference<Histogram> getHistogram(StringRef group, StringRef op, Unit unit) {
std::string group_str = group.toString();
std::string op_str = op.toString();
std::string name = generateName(group_str, op_str);
HistogramRegistry& registry = GetHistogramRegistry();
Histogram* h = registry.lookupHistogram(name);
if (!h) {
h = new Histogram(group_str, op_str, unit, registry);
registry.registerHistogram(h);
return Reference<Histogram>(h);
} else {
return Reference<Histogram>::addRef(h);
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}
}
// This histogram buckets samples into powers of two.
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inline void sample(uint32_t sample) {
size_t idx;
#ifdef _WIN32
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unsigned long index;
// _BitScanReverse sets index to the position of the first non-zero bit, so
// _BitScanReverse(sample) ~= log_2(sample). _BitScanReverse returns false if
// sample is zero.
idx = _BitScanReverse(&index, sample) ? index : 0;
#else
// __builtin_clz counts the leading zeros in its uint32_t argument. So, 31-clz ~= log_2(sample).
// __builtin_clz(0) is undefined.
idx = sample ? (31 - __builtin_clz(sample)) : 0;
#endif
ASSERT(idx < 32);
buckets[idx]++;
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}
inline void sampleSeconds(double delta) {
uint64_t delta_usec = (delta * 1000000);
if (delta_usec > UINT32_MAX) {
sample(UINT32_MAX);
} else {
sample((uint32_t)(delta * 1000000)); // convert to microseconds and truncate to integer
}
}
void clear() {
for (uint32_t& i : buckets) {
i = 0;
}
}
void writeToLog();
std::string name() { return generateName(this->group, this->op); }
std::string const group;
std::string const op;
Unit const unit;
HistogramRegistry& registry;
uint32_t buckets[32];
};
#endif // FLOW_HISTOGRAM_H