testing: implement testing.B.Loop

Initial implementation for testing.B.Loop,
right now the calculation of b.N are still done in the old fasion way,
as of now b.Loop is merely an alias for the old loop over b.N.

For #61515.

Change-Id: If211d0acc5f0c33df530096dceafe0b947ab0c8e
Reviewed-on: https://go-review.googlesource.com/c/go/+/608798
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Run-TryBot: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

diff --git a/api/next/61515.txt b/api/next/61515.txt
new file mode 100644 (file)
index 0000000..e797156
--- /dev/null
+++ b/api/next/61515.txt
@@ -0,0 +1 @@
+pkg testing, method (*B) Loop() bool #61515

diff --git a/doc/next/6-stdlib/99-minor/testing/61515.md b/doc/next/6-stdlib/99-minor/testing/61515.md
new file mode 100644 (file)
index 0000000..f724eb1
--- /dev/null
+++ b/doc/next/6-stdlib/99-minor/testing/61515.md
@@ -0,0 +1 @@
+Benchmarks can use the new [B.Loop] method in `for b.Loop() { ... }` loops to determine if iteration should continue.

diff --git a/src/testing/benchmark.go b/src/testing/benchmark.go
index 5591cd4e4d4a9318e0b67f5a12e5db4b398db928..0271308346fa7cc6409beae9a49f8b4ad3925d0b 100644 (file)
--- a/src/testing/benchmark.go
+++ b/src/testing/benchmark.go
@@ -113,6 +113,8 @@ type B struct {
        netBytes  uint64
        // Extra metrics collected by ReportMetric.
        extra map[string]float64
+       // Remaining iterations of Loop() to be executed in benchFunc.
+       loopN int
 }
 
 // StartTimer starts timing a test. This function is called automatically
@@ -187,6 +189,7 @@ func (b *B) runN(n int) {
        runtime.GC()
        b.resetRaces()
        b.N = n
+       b.loopN = n
        b.parallelism = 1
        b.ResetTimer()
        b.StartTimer()
@@ -349,6 +352,16 @@ func (b *B) ReportMetric(n float64, unit string) {
        b.extra[unit] = n
 }
 
+// Loop returns true until b.N calls has been made to it.
+//
+// A benchmark should either use Loop or contain an explicit loop from 0 to b.N, but not both.
+// After the benchmark finishes, b.N will contain the total number of calls to op, so the benchmark
+// may use b.N to compute other average metrics.
+func (b *B) Loop() bool {
+       b.loopN--
+       return b.loopN >= 0
+}
+
 // BenchmarkResult contains the results of a benchmark run.
 type BenchmarkResult struct {
        N         int           // The number of iterations.

diff --git a/src/testing/benchmark_test.go b/src/testing/benchmark_test.go
index 66f555d1f1d05d2470a27fef2b733e5e1d0df81e..b5ad213fb39e139fb02e4ec169a9032c060dd16f 100644 (file)
--- a/src/testing/benchmark_test.go
+++ b/src/testing/benchmark_test.go
@@ -127,6 +127,22 @@ func TestRunParallelSkipNow(t *testing.T) {
        })
 }
 
+func TestLoopEqualsRangeOverBN(t *testing.T) {
+       // Verify that b.N and the b.Loop() iteration count match.
+       var nIterated, nInfered int
+       testing.Benchmark(func(b *testing.B) {
+               i := 0
+               for b.Loop() {
+                       i++
+               }
+               nIterated = i
+               nInfered = b.N
+       })
+       if nIterated != nInfered {
+               t.Fatalf("Iteration of the two different benchmark loop flavor differs, got %d iterations want %d", nIterated, nInfered)
+       }
+}
+
 func ExampleB_RunParallel() {
        // Parallel benchmark for text/template.Template.Execute on a single object.
        testing.Benchmark(func(b *testing.B) {