Add support for execution traces (#23)

* Add support for execution traces

- Only available on Go 1.7+

* Fix support for Go 1.6 and earlier

profile.go

@@ -17,6 +17,7 @@ const (
 	cpuMode = iota
 	memMode
 	blockMode
+	traceMode
 )
 
 type profile struct {
@@ -181,6 +182,21 @@ func Start(options ...func(*profile)) interface {
 			runtime.SetBlockProfileRate(0)
 			logf("profile: block profiling disabled, %s", fn)
 		}
+
+	case traceMode:
+		fn := filepath.Join(path, "trace.out")
+		f, err := os.Create(fn)
+		if err != nil {
+			log.Fatalf("profile: could not create trace output file %q: %v", fn, err)
+		}
+		if err := startTrace(f); err != nil {
+			log.Fatalf("profile: could not start trace: %v", err)
+		}
+		logf("profile: trace enabled, %s", fn)
+		prof.closer = func() {
+			stopTrace()
+			logf("profile: trace disabled, %s", fn)
+		}
 	}
 
 	if !prof.noShutdownHook {

trace.go

@@ -0,0 +1,11 @@
+// +build go1.7
+
+package profile
+
+import "runtime/trace"
+
+// Trace profile controls if execution tracing will be enabled. It disables any previous profiling settings.
+func TraceProfile(p *profile) { p.mode = traceMode }
+
+var startTrace = trace.Start
+var stopTrace = trace.Stop

trace16.go

@@ -0,0 +1,10 @@
+// +build !go1.7
+
+package profile
+
+import "io"
+
+// mock trace support for Go 1.6 and earlier.
+
+func startTrace(w io.Writer) error { return nil }
+func stopTrace()                   {}

trace_test.go

@@ -0,0 +1,10 @@
+// +build go1.7
+
+package profile_test
+
+import "github.com/pkg/profile"
+
+func ExampleTraceProfile() {
+	// use execution tracing, rather than the default cpu profiling.
+	defer profile.Start(profile.TraceProfile).Stop()
+}