foundationdb/flow/Histogram.cpp

/*
 * Histogram.cpp
 *
 * 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.
 */

#include <flow/Histogram.h>
#include <flow/flow.h>
#include <flow/UnitTest.h>
// TODO: remove dependency on fdbrpc.

// we need to be able to check if we're in simulation so that the histograms are properly
// scoped to the right "machine".
// either we pull g_simulator into flow, or flow (and the I/O path) will be unable to log performance
// metrics.
#include <fdbrpc/simulator.h>

// pull in some global pointers too:  These types are implemented in fdbrpc/sim2.actor.cpp, which is not available here.
// Yuck. If you're not using the simulator, these will remain null, and all should be well.

// TODO: create a execution context abstraction that allows independent flow instances within a process.
// The simulator would be the main user of it, and histogram would be the only other user (for now).
ISimulator* g_pSimulator = nullptr;
thread_local ISimulator::ProcessInfo* ISimulator::currentProcess = nullptr;

// Fallback registry when we're not in simulation -- if we had execution contexts we wouldn't need to check if
// we have a simulated contex here; we'd just use the current context regardless.
static HistogramRegistry* globalHistograms = nullptr;

#pragma region HistogramRegistry

HistogramRegistry& GetHistogramRegistry() {
	ISimulator::ProcessInfo* info = g_simulator.getCurrentProcess();

	if (info) {
		// in simulator; scope histograms to simulated process
		return info->histograms;
	}
	// avoid link order issues where the registry hasn't been initialized, but we're
	// instantiating a histogram
	if (globalHistograms == nullptr) {
		// Note:  This will show up as a leak on shutdown, but we're OK with that.
		globalHistograms = new HistogramRegistry();
	}
	return *globalHistograms;
}

void HistogramRegistry::registerHistogram(Histogram* h) {
	if (histograms.find(h->name()) != histograms.end()) {
		TraceEvent(SevError, "HistogramDoubleRegistered").detail("group", h->group).detail("op", h->op);
		ASSERT(false);
	}
	histograms.insert(std::pair<std::string, Histogram*>(h->name(), h));
}

void HistogramRegistry::unregisterHistogram(Histogram* h) {
	std::string name = h->name();
	if (histograms.find(name) == histograms.end()) {
		TraceEvent(SevError, "HistogramNotRegistered").detail("group", h->group).detail("op", h->op);
	}
	int count = histograms.erase(name);
	ASSERT(count == 1);
}

Histogram* HistogramRegistry::lookupHistogram(std::string name) {
	auto h = histograms.find(name);
	if (h == histograms.end()) {
		return nullptr;
	}
	return h->second;
}

void HistogramRegistry::logReport() {
	for (auto& i : histograms) {
		i.second->writeToLog();
		i.second->clear();
	}
}

#pragma endregion // HistogramRegistry

#pragma region Histogram

const std::unordered_map<Histogram::Unit, std::string> Histogram::UnitToStringMapper = {
	{ Histogram::Unit::microseconds, "microseconds" },
	{ Histogram::Unit::bytes, "bytes" },
	{ Histogram::Unit::bytes_per_second, "bytes_per_second" }
};

void Histogram::writeToLog() {
	bool active = false;
	for (uint32_t i = 0; i < 32; i++) {
		if (buckets[i]) {
			active = true;
			break;
		}
	}
	if (!active) {
		return;
	}

	TraceEvent e(SevInfo, "Histogram");
	e.detail("Group", group).detail("Op", op).detail("Unit", UnitToStringMapper.at(unit));

	for (uint32_t i = 0; i < 32; i++) {
		uint32_t value = ((uint32_t)1) << (i + 1);

		if (buckets[i]) {
			switch (unit) {
			case Unit::microseconds:
				e.detail(format("LessThan%u.%03u", value / 1000, value % 1000), buckets[i]);
				break;
			case Unit::bytes:
			case Unit::bytes_per_second:
				e.detail(format("LessThan%u", value), buckets[i]);
				break;
			default:
				ASSERT(false);
			}
		}
	}
}

#pragma endregion // Histogram

TEST_CASE("/flow/histogram/smoke_test") {

	{
		Reference<Histogram> h =
		    Histogram::getHistogram(LiteralStringRef("smoke_test"), LiteralStringRef("counts"), Histogram::Unit::bytes);

		h->sample(0);
		ASSERT(h->buckets[0] == 1);
		h->sample(1);
		ASSERT(h->buckets[0] == 2);

		h->sample(2);
		ASSERT(h->buckets[1] == 1);

		GetHistogramRegistry().logReport();

		ASSERT(h->buckets[0] == 0);
		h->sample(0);
		ASSERT(h->buckets[0] == 1);
		h = Histogram::getHistogram(
		    LiteralStringRef("smoke_test"), LiteralStringRef("counts2"), Histogram::Unit::bytes);

		// confirm that old h was deallocated.
		h = Histogram::getHistogram(LiteralStringRef("smoke_test"), LiteralStringRef("counts"), Histogram::Unit::bytes);
		ASSERT(h->buckets[0] == 0);

		h = Histogram::getHistogram(
		    LiteralStringRef("smoke_test"), LiteralStringRef("times"), Histogram::Unit::microseconds);

		h->sampleSeconds(0.000000);
		h->sampleSeconds(0.0000019);
		ASSERT(h->buckets[0] == 2);
		h->sampleSeconds(0.0000021);
		ASSERT(h->buckets[1] == 1);
		h->sampleSeconds(0.000015);
		ASSERT(h->buckets[3] == 1);

		h->sampleSeconds(4400.0);
		ASSERT(h->buckets[31] == 1);

		GetHistogramRegistry().logReport();
	}

	// h has been deallocated.  Does this crash?
	GetHistogramRegistry().logReport();

	return Void();
}