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  	if parallelStart.Load() != parallelStop.Load() {
    22  		panic("testing: AllocsPerRun called during parallel test")
    23  	}
    24  	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
    25  
    26  	// Warm up the function
    27  	f()
    28  
    29  	// Measure the starting statistics
    30  	var memstats runtime.MemStats
    31  	runtime.ReadMemStats(&memstats)
    32  	mallocs := 0 - memstats.Mallocs
    33  
    34  	// Run the function the specified number of times
    35  	for i := 0; i < runs; i++ {
    36  		f()
    37  	}
    38  
    39  	// Read the final statistics
    40  	runtime.ReadMemStats(&memstats)
    41  	mallocs += memstats.Mallocs
    42  
    43  	// Average the mallocs over the runs (not counting the warm-up).
    44  	// We are forced to return a float64 because the API is silly, but do
    45  	// the division as integers so we can ask if AllocsPerRun()==1
    46  	// instead of AllocsPerRun()<2.
    47  	return float64(mallocs / uint64(runs))
    48  }
    49
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