libgo/go/testing/allocs.go

   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
   5 package testing
   6
   7 import (
   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.
  20 func 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 }