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1 // Copyright 2013 The Go Authors. All rights reserved.
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2 // Use of this source code is governed by a BSD-style
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3 // license that can be found in the LICENSE file.
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4
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5 package testing
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6
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7 import (
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8 "runtime"
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9 )
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10
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11 // AllocsPerRun returns the average number of allocations during calls to f.
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12 // Although the return value has type float64, it will always be an integral value.
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13 //
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14 // To compute the number of allocations, the function will first be run once as
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15 // a warm-up. The average number of allocations over the specified number of
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16 // runs will then be measured and returned.
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17 //
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18 // AllocsPerRun sets GOMAXPROCS to 1 during its measurement and will restore
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19 // it before returning.
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20 func AllocsPerRun(runs int, f func()) (avg float64) {
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21 defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
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22
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23 // Warm up the function
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24 f()
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25
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26 // Measure the starting statistics
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27 var memstats runtime.MemStats
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28 runtime.ReadMemStats(&memstats)
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29 mallocs := 0 - memstats.Mallocs
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30
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31 // Run the function the specified number of times
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32 for i := 0; i < runs; i++ {
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33 f()
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34 }
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35
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36 // Read the final statistics
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37 runtime.ReadMemStats(&memstats)
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38 mallocs += memstats.Mallocs
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39
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40 // Average the mallocs over the runs (not counting the warm-up).
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41 // We are forced to return a float64 because the API is silly, but do
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42 // the division as integers so we can ask if AllocsPerRun()==1
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43 // instead of AllocsPerRun()<2.
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44 return float64(mallocs / uint64(runs))
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45 }
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