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Add a web server to report memory utilization
New -p (port) flag and environment variable specifies listen port. Coalesce fmt.Print some statements to reduce stdout race window. And improve code comments in pingtimes and cw_put.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,71 @@ | ||
| package util | ||
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| import ( | ||
| "fmt" | ||
| "log" | ||
| "net/http" | ||
| "runtime" | ||
| "time" | ||
| ) | ||
|
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| func bToMb(b uint64) uint64 { | ||
| return b / 1024 / 1024 | ||
| } | ||
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| // StartServer is a goroutine that runs up a web server to listen on the given | ||
| // port, and sets up handlers for two endpoints: "/ping" serves a simple HTTP | ||
| // reply that includes the request URI and current time; "/memstats" serves a | ||
| // simple HTTP page showing current golang memory utilization. The port | ||
| // argument should be a valid port number that you can listen on. | ||
| // | ||
| // StartServer never returns. Invoke it with go StartServer(yourPort). | ||
| func StartServer(port int) { | ||
| http.HandleFunc("/ping", pongReply) | ||
| http.HandleFunc("/memstats", memStatsReply) | ||
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| max := 5 // 5 tries = 15 seconds (linear backoff -- 5th triangular number) | ||
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| addr := fmt.Sprintf(":%d", port) | ||
| // The ListenAndServe call should not return. If it does the address may be in use so retry below. | ||
| err := http.ListenAndServe(addr, nil) | ||
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| tries := 0 | ||
| for tries < max { | ||
| tries++ | ||
| // sleep a little while (longer each time through the loop) | ||
| log.Println(err, "sleep", tries) | ||
| time.Sleep(time.Duration(tries) * time.Second) | ||
| // now try again ... it may take a while for a previous instance to exit | ||
| err = http.ListenAndServe(addr, nil) | ||
| } | ||
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| if err != nil { | ||
| // if error is anything else print the error and return | ||
| log.Println(err) | ||
| } | ||
| } | ||
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| func pongReply(w http.ResponseWriter, r *http.Request) { | ||
| now := time.Now() | ||
| fmt.Fprintln(w, "<h1>pong</h1><p>reply to", r.URL.Path, "@", now) | ||
| log.Println("pongReply", r.RemoteAddr) | ||
| } | ||
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| func memStatsReply(w http.ResponseWriter, r *http.Request) { | ||
| // with thanks from https://golangcode.com/print-the-current-memory-usage/ | ||
| var m runtime.MemStats | ||
| runtime.ReadMemStats(&m) | ||
| active := m.Mallocs - m.Frees | ||
| alloc := bToMb(m.Alloc) | ||
| fmt.Fprintln(w, "<h1>MemStats</h1>\n<p>", time.Now()) | ||
| // The number of live objects is Mallocs - Frees. | ||
| fmt.Fprintf(w, "<br>Active Objects = %v\n", active) | ||
| // HeapAlloc is bytes of allocated heap objects. | ||
| fmt.Fprintf(w, "<br>Active Bytes = %v MiB\n", alloc) | ||
| // Sys is the total bytes of memory obtained from the OS. | ||
| fmt.Fprintf(w, "<br>OS Bytes = %v MiB\n", bToMb(m.Sys)) | ||
| // NumGC is the number of completed GC cycles. | ||
| fmt.Fprintf(w, "<br>Num GCs = %v\n</p>", m.NumGC) | ||
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| log.Println("pongReply", r.RemoteAddr, active, alloc) | ||
| } |