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  }
    46
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