testing: add tracing support

testing part of tracing functionality:
https://docs.google.com/document/u/1/d/1FP5apqzBgr7ahCCgFO-yoVhk4YZrNIDNf9RybngBc14/pub
Full change:
https://codereview.appspot.com/146920043

Change-Id: Ia3c2c4417106937d5775b0e7064db92c1fc36679
Reviewed-on: https://go-review.googlesource.com/1461
Reviewed-by: Russ Cox <rsc@golang.org>

diff --git a/src/testing/testing.go b/src/testing/testing.go
index e54a3b8ce4dfca3a0e01dc2d35f95d269d035141..966b5466b711faaf7d186a45ff167394fd7b8ff2 100644 (file)
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -175,6 +175,7 @@ var (
        cpuProfile       = flag.String("test.cpuprofile", "", "write a cpu profile to the named file during execution")
        blockProfile     = flag.String("test.blockprofile", "", "write a goroutine blocking profile to the named file after execution")
        blockProfileRate = flag.Int("test.blockprofilerate", 1, "if >= 0, calls runtime.SetBlockProfileRate()")
+       trace            = flag.String("test.trace", "", "write an execution trace to the named file after execution")
        timeout          = flag.Duration("test.timeout", 0, "if positive, sets an aggregate time limit for all tests")
        cpuListStr       = flag.String("test.cpu", "", "comma-separated list of number of CPUs to use for each test")
        parallel         = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "maximum test parallelism")
@@ -600,6 +601,19 @@ func before() {
                }
                // Could save f so after can call f.Close; not worth the effort.
        }
+       if *trace != "" {
+               f, err := os.Create(toOutputDir(*trace))
+               if err != nil {
+                       fmt.Fprintf(os.Stderr, "testing: %s", err)
+                       return
+               }
+               if err := pprof.StartTrace(f); err != nil {
+                       fmt.Fprintf(os.Stderr, "testing: can't start tracing: %s", err)
+                       f.Close()
+                       return
+               }
+               // Could save f so after can call f.Close; not worth the effort.
+       }
        if *blockProfile != "" && *blockProfileRate >= 0 {
                runtime.SetBlockProfileRate(*blockProfileRate)
        }
@@ -614,6 +628,9 @@ func after() {
        if *cpuProfile != "" {
                pprof.StopCPUProfile() // flushes profile to disk
        }
+       if *trace != "" {
+               pprof.StopTrace() // flushes trace to disk
+       }
        if *memProfile != "" {
                f, err := os.Create(toOutputDir(*memProfile))
                if err != nil {