1// Copyright 2013 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package testing
6
7import (
8	"runtime"
9)
10
11// AllocsPerRun returns the average number of allocations during calls to f.
12// Although the return value has type float64, it will always be an integral value.
13//
14// To compute the number of allocations, the function will first be run once as
15// a warm-up. The average number of allocations over the specified number of
16// runs will then be measured and returned.
17//
18// AllocsPerRun sets GOMAXPROCS to 1 during its measurement and will restore
19// it before returning.
20func AllocsPerRun(runs int, f func()) (avg float64) {
21	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
22
23	// Warm up the function
24	f()
25
26	// Measure the starting statistics
27	var memstats runtime.MemStats
28	runtime.ReadMemStats(&memstats)
29	mallocs := 0 - memstats.Mallocs
30
31	// Run the function the specified number of times
32	for i := 0; i < runs; i++ {
33		f()
34	}
35
36	// Read the final statistics
37	runtime.ReadMemStats(&memstats)
38	mallocs += memstats.Mallocs
39
40	// Average the mallocs over the runs (not counting the warm-up).
41	// We are forced to return a float64 because the API is silly, but do
42	// the division as integers so we can ask if AllocsPerRun()==1
43	// instead of AllocsPerRun()<2.
44	return float64(mallocs / uint64(runs))
45}
46