runtime/pprof: Remove SIGPROF if the last event is stopped.

[WangLeonard]

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[WangLeonard]

Hi, I added the following print and did an experiment

diff --git a/src/net/http/pprof/pprof.go b/src/net/http/pprof/pprof.go
index 89d5151c1f..c5dfe375d3 100644
--- a/src/net/http/pprof/pprof.go
+++ b/src/net/http/pprof/pprof.go
@@ -151,6 +151,7 @@ func Profile(w http.ResponseWriter, r *http.Request) {
        case "timer":
                err = pprof.StartCPUProfile(w)
        case "cycles":
+               println("StartCPUProfileWithConfig")
                err = pprof.StartCPUProfileWithConfig(pprof.CPUCycles(w, period))
        case "instructions":
                err = pprof.StartCPUProfileWithConfig(pprof.CPUInstructions(w, period))
@@ -182,6 +183,7 @@ func Profile(w http.ResponseWriter, r *http.Request) {
        }
 
        sleep(r, time.Duration(sec)*time.Second)
+       println("StopCPUProfile")
        pprof.StopCPUProfile()
 }
 
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index f7a57d75cc..0f25566238 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -4644,10 +4644,12 @@ func setcpuprofileconfig(eventId cpuEvent, profConfig *cpuProfileConfig) {
                        for i := _CPUPROF_FIRST_EVENT; i < _CPUPROF_EVENTS_MAX; i++ {
                                if prof[i].config != nil {
                                        eventsRunning = true
+                                       println("eventsRunning = true")
                                        break
                                }
                        }
                        if eventsRunning == false {
+                               println("setProcessCPUProfiler(nil)")
                                setProcessCPUProfiler(nil)
                        }
                } else {

when I run net/http/pprof/examples/goroutine.go

and curl for a cycles event profile

It will print:

go run goroutine.go
StartCPUProfileWithConfig
StopCPUProfile
eventsRunning = true

Note, I only create one event, and when it is done, call pprof.StopCPUProfile().

It will set eventsRunning = true, and miss setProcessCPUProfiler(nil) , further miss Restore SIGPROF.

Is this as expected? Does it need to be fixed?

Thank you!

[WangLeonard]

friendly ping...
Is this MR correct or maybe I am thinking wrong somewhere?