Source: allocs.go in package testing

Source File
	allocs.go

Belonging Package
	testing


package testing

import (
	"runtime"
)

AllocsPerRun returns the average number of allocations during calls to f. Although the return value has type float64, it will always be an integral value. To compute the number of allocations, the function will first be run once as a warm-up. The average number of allocations over the specified number of runs will then be measured and returned. AllocsPerRun sets GOMAXPROCS to 1 during its measurement and will restore it before returning.

func AllocsPerRun(runs int, f func()) (avg float64) {
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))

Warm up the function

f()

Measure the starting statistics

	var memstats runtime.MemStats
	runtime.ReadMemStats(&memstats)
	mallocs := 0 - memstats.Mallocs

Run the function the specified number of times

	for i := 0; i < runs; i++ {
		f()
	}

Read the final statistics

	runtime.ReadMemStats(&memstats)
	mallocs += memstats.Mallocs

Average the mallocs over the runs (not counting the warm-up). We are forced to return a float64 because the API is silly, but do the division as integers so we can ask if AllocsPerRun()==1 instead of AllocsPerRun()<2.

	return float64(mallocs / uint64(runs))


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