code review 6443115: pprof: add contention profiling

src/pkg/runtime/pprof/pprof.go

Index: src/pkg/runtime/pprof/pprof.go
===================================================================
--- a/src/pkg/runtime/pprof/pprof.go
+++ b/src/pkg/runtime/pprof/pprof.go
@@ -36,6 +36,7 @@
 //	goroutine    - stack traces of all current goroutines
 //	heap         - a sampling of all heap allocations
 //	threadcreate - stack traces that led to the creation of new OS threads
+//	block        - stack traces that led to blocking on synchronization primitives
 //
 // These predefine profiles maintain themselves and panic on an explicit
 // Add or Remove method call.
@@ -76,6 +77,12 @@
 	write: writeHeap,
 }
 
+var blockProfile = &Profile{
+	name:  "block",
+	count: countBlock,
+	write: writeBlock,
+}
+
 func lockProfiles() {
 	profiles.mu.Lock()
 	if profiles.m == nil {
@@ -84,6 +91,7 @@
 			"goroutine":    goroutineProfile,
 			"threadcreate": threadcreateProfile,
 			"heap":         heapProfile,
+			"block":        blockProfile,
 		}
 	}
 }
@@ -600,3 +608,60 @@
 	runtime.SetCPUProfileRate(0)
 	<-cpu.done
 }
+
+type byCycles []runtime.BlockProfileRecord
+
+func (x byCycles) Len() int           { return len(x) }
+func (x byCycles) Swap(i, j int)      { x[i], x[j] = x[j], x[i] }
+func (x byCycles) Less(i, j int) bool { return x[i].Cycles > x[j].Cycles }
+
+// countBlock returns the number of records in the blocking profile.
+func countBlock() int {
+	n, _ := runtime.BlockProfile(nil)
+	return n
+}
+
+// writeBlock writes the current blocking profile to w.
+func writeBlock(w io.Writer, debug int) error {
+	var p []runtime.BlockProfileRecord
+	n, ok := runtime.BlockProfile(nil)
+	for {
+		p = make([]runtime.BlockProfileRecord, n+50)
+		n, ok = runtime.BlockProfile(p)
+		if ok {
+			p = p[:n]
+			break
+		}
+	}
+
+	sort.Sort(byCycles(p))
+
+	b := bufio.NewWriter(w)
+	var tw *tabwriter.Writer
+	w = b
+	if debug > 0 {
+		tw = tabwriter.NewWriter(w, 1, 8, 1, '\t', 0)
+		w = tw
+	}
+
+	fmt.Fprintf(w, "--- contention:\n")
+	fmt.Fprintf(w, "cycles/second=%v\n", runtime_cyclesPerSecond())
+	for i := range p {
+		r := &p[i]
+		fmt.Fprintf(w, "%v %v @", r.Cycles, r.Count)
+		for _, pc := range r.Stack() {
+			fmt.Fprintf(w, " %#x", pc)
+		}
+		fmt.Fprint(w, "\n")
+		if debug > 0 {
+			printStackRecord(w, r.Stack(), false)
+		}
+	}
+
+	if tw != nil {
+		tw.Flush()
+	}
+	return b.Flush()
+}
+
+func runtime_cyclesPerSecond() int64