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// This source file is part of the Swift.org open source project
//
// Copyright (c) 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//
// WallClockTimeMetric.swift
// Performance metric measuring how long it takes code to execute
//
/// This metric uses the system uptime to keep track of how much time passes
/// between starting and stopping measuring.
internal final class WallClockTimeMetric: PerformanceMetric {
static let name = "org.swift.XCTPerformanceMetric_WallClockTime"
typealias Measurement = TimeInterval
private var startTime: TimeInterval?
var measurements: [Measurement] = []
func startMeasuring() {
startTime = currentTime()
}
func stopMeasuring() {
guard let startTime = startTime else { fatalError("Must start measuring before stopping measuring") }
let stopTime = currentTime()
measurements.append(stopTime-startTime)
}
private let maxRelativeStandardDeviation = 10.0
private let standardDeviationNegligibilityThreshold = 0.1
func calculateResults() -> String {
let results = [
String(format: "average: %.3f", measurements.average),
String(format: "relative standard deviation: %.3f%%", measurements.relativeStandardDeviation),
"values: [\(measurements.map({ String(format: "%.6f", $0) }).joined(separator: ", "))]",
"performanceMetricID:\(type(of: self).name)",
String(format: "maxPercentRelativeStandardDeviation: %.3f%%", maxRelativeStandardDeviation),
String(format: "maxStandardDeviation: %.3f", standardDeviationNegligibilityThreshold),
]
return "[Time, seconds] \(results.joined(separator: ", "))"
}
func failureMessage() -> String? {
let relativeStandardDeviation = measurements.relativeStandardDeviation
if (relativeStandardDeviation > maxRelativeStandardDeviation &&
measurements.standardDeviation > standardDeviationNegligibilityThreshold) {
return String(format: "The relative standard deviation of the measurements is %.3f%% which is higher than the max allowed of %.3f%%.", relativeStandardDeviation, maxRelativeStandardDeviation)
}
return nil
}
private func currentTime() -> TimeInterval {
return ProcessInfo.processInfo.systemUptime
}
}
private extension Collection where Index: ExpressibleByIntegerLiteral, Iterator.Element == WallClockTimeMetric.Measurement {
var average: WallClockTimeMetric.Measurement {
return self.reduce(0, +) / Double(Int(count))
}
var standardDeviation: WallClockTimeMetric.Measurement {
let average = self.average
let squaredDifferences = self.map({ pow($0 - average, 2.0) })
let variance = squaredDifferences.reduce(0, +) / Double(Int(count-1))
return sqrt(variance)
}
var relativeStandardDeviation: Double {
return (standardDeviation*100) / average
}
}
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