Module: Benchmark

The Benchmark module provides methods to measure and report the time used to execute Ruby code.

Measure the time to construct the string given by the expression "a"*1_000_000:
```
require 'benchmark'

puts Benchmark.measure { "a"*1_000_000 }
```
On my machine (FreeBSD 3.2 on P5, 100MHz) this generates:
```
1.166667   0.050000   1.216667 (  0.571355)
```
This report shows the user CPU time, system CPU time, the sum of the user and system CPU times, and the elapsed real time. The unit of time is seconds.

Do some experiments sequentially using the #bm method:

require 'benchmark'

n = 50000
Benchmark.bm do |x|
  x.report { for i in 1..n; a = "1"; end }
  x.report { n.times do   ; a = "1"; end }
  x.report { 1.upto(n) do ; a = "1"; end }
end

The result:

    user     system      total        real
1.033333   0.016667   1.016667 (  0.492106)
1.483333   0.000000   1.483333 (  0.694605)
1.516667   0.000000   1.516667 (  0.711077)

Continuing the previous example, put a label in each report:

require 'benchmark'

n = 50000
Benchmark.bm(7) do |x|
  x.report("for:")   { for i in 1..n; a = "1"; end }
  x.report("times:") { n.times do   ; a = "1"; end }
  x.report("upto:")  { 1.upto(n) do ; a = "1"; end }
end

The result:

             user     system      total        real
for:     1.050000   0.000000   1.050000 (  0.503462)
times:   1.533333   0.016667   1.550000 (  0.735473)
upto:    1.500000   0.016667   1.516667 (  0.711239)

The times for some benchmarks depend on the order in which items are run. These differences are due to the cost of memory allocation and garbage collection. To avoid these discrepancies, the #bmbm method is provided. For example, to compare ways to sort an array of floats:

require 'benchmark'

array = (1..1000000).map { rand }

Benchmark.bmbm do |x|
  x.report("sort!") { array.dup.sort! }
  x.report("sort")  { array.dup.sort  }
end

The result:

Rehearsal -----------------------------------------
sort!  11.928000   0.010000  11.938000 ( 12.756000)
sort   13.048000   0.020000  13.068000 ( 13.857000)
------------------------------- total: 25.006000sec

            user     system      total        real
sort!  12.959000   0.010000  12.969000 ( 13.793000)
sort   12.007000   0.000000  12.007000 ( 12.791000)

Report statistics of sequential experiments with unique labels, using the #benchmark method:

require 'benchmark'

n = 50000
Benchmark.benchmark(" "*7 + CAPTION, 7, FMTSTR, ">total:", ">avg:") do |x|
  tf = x.report("for:")   { for i in 1..n; a = "1"; end }
  tt = x.report("times:") { n.times do   ; a = "1"; end }
  tu = x.report("upto:")  { 1.upto(n) do ; a = "1"; end }
  [tf+tt+tu, (tf+tt+tu)/3]
end

The result:

             user     system      total        real
for:     1.016667   0.016667   1.033333 (  0.485749)
times:   1.450000   0.016667   1.466667 (  0.681367)
upto:    1.533333   0.000000   1.533333 (  0.722166)
>total:  4.000000   0.033333   4.033333 (  1.889282)
>avg:    1.333333   0.011111   1.344444 (  0.629761)

Classes
Job	A Job is a sequence of labelled blocks to be processed by the Benchmark.bmbm method. It is of little direct interest to the user.
Report	This class is used by the Benchmark.benchmark and Benchmark.bm methods. It is of little direct interest to the user.
Tms	A data object, representing the times associated with a benchmark measurement.

Constants
BENCHMARK_VERSION
CAPTION	The default caption string (heading above the output times).
FMTSTR	The default format string used to display times. See also Benchmark::Tms#format.

Public Methods
benchmark	Invokes the block with a `Benchmark::Report` object, which may be used to collect and report on the results of individual benchmark tests. Reserves label_width leading spaces for labels on each line. Prints caption at the top of the report, and uses fmt to format each line. If the block returns an array of `Benchmark::Tms` objects, these will be used to format additional lines of output. If label parameters are given, these are used to label these extra lines.
bm	A simple interface to the #benchmark method, #bm is generates sequential reports with labels. The parameters have the same meaning as for #benchmark.
bmbm	Sometimes benchmark results are skewed because code executed earlier encounters different garbage collection overheads than that run later. #bmbm attempts to minimize this effect by running the tests twice, the first time as a rehearsal in order to get the runtime environment stable, the second time for real. `GC.start` is executed before the start of each of the real timings; the cost of this is not included in the timings. In reality, though, there’s only so much that #bmbm can do, and the results are not guaranteed to be isolated from garbage collection and other effects.
measure	Returns the time used to execute the given block as a Benchmark::Tms object.
realtime	Returns the elapsed real time used to execute the given block.
times

Benchmark

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