main: save memory profile every 60 seconds

...and move all profiling functionality to its own file, as
the main function is already long enough.

Periodically saving the memory profile allows capturing the used
memory during normal operation, as opposed to on exit, where the
kernel has already issued FORGETs for all inodes.

This functionality has been used to create the memory profile shown
in https://github.com/rfjakob/gocryptfs/issues/132 .

main.go

@@ -3,11 +3,8 @@ package main
 import (
 	"fmt"
 	"os"
-
 	"path/filepath"
 	"runtime"
-	"runtime/pprof"
-	"runtime/trace"
 	"strconv"
 	"strings"
 	"time"
@@ -208,49 +205,18 @@ func main() {
 	}
 	// "-cpuprofile"
 	if args.cpuprofile != "" {
-		tlog.Info.Printf("Writing CPU profile to %s", args.cpuprofile)
-		var f *os.File
-		f, err = os.Create(args.cpuprofile)
-		if err != nil {
-			tlog.Fatal.Println(err)
-			os.Exit(exitcodes.Profiler)
-		}
-		err = pprof.StartCPUProfile(f)
-		if err != nil {
-			tlog.Fatal.Println(err)
-			os.Exit(exitcodes.Profiler)
-		}
-		defer pprof.StopCPUProfile()
+		onExitFunc := setupCpuprofile(args.cpuprofile)
+		defer onExitFunc()
 	}
 	// "-memprofile"
 	if args.memprofile != "" {
-		tlog.Info.Printf("Writing mem profile to %s", args.memprofile)
-		var f *os.File
-		f, err = os.Create(args.memprofile)
-		if err != nil {
-			tlog.Fatal.Println(err)
-			os.Exit(exitcodes.Profiler)
-		}
-		defer func() {
-			pprof.WriteHeapProfile(f)
-			f.Close()
-			return
-		}()
+		onExitFunc := setupMemprofile(args.memprofile)
+		defer onExitFunc()
 	}
 	// "-trace"
 	if args.trace != "" {
-		tlog.Info.Printf("Writing execution trace to %s", args.trace)
-		f, err := os.Create(args.trace)
-		if err != nil {
-			tlog.Fatal.Println(err)
-			os.Exit(exitcodes.Profiler)
-		}
-		err = trace.Start(f)
-		if err != nil {
-			tlog.Fatal.Println(err)
-			os.Exit(exitcodes.Profiler)
-		}
-		defer trace.Stop()
+		onExitFunc := setupTrace(args.trace)
+		defer onExitFunc()
 	}
 	if args.cpuprofile != "" || args.memprofile != "" || args.trace != "" {
 		tlog.Info.Printf("Note: You must unmount gracefully, otherwise the profile file(s) will stay empty!\n")

profiling.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"os"
+	"runtime/pprof"
+	"runtime/trace"
+	"time"
+
+	"github.com/rfjakob/gocryptfs/internal/exitcodes"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+// setupCpuprofile is called to handle a non-empty "-cpuprofile" cli argument
+func setupCpuprofile(cpuprofileArg string) func() {
+	tlog.Info.Printf("Writing CPU profile to %s", cpuprofileArg)
+	f, err := os.Create(cpuprofileArg)
+	if err != nil {
+		tlog.Fatal.Println(err)
+		os.Exit(exitcodes.Profiler)
+	}
+	err = pprof.StartCPUProfile(f)
+	if err != nil {
+		tlog.Fatal.Println(err)
+		os.Exit(exitcodes.Profiler)
+	}
+	return func() {
+		pprof.StopCPUProfile()
+	}
+}
+
+// setupTrace is called to handle a non-empty "-memprofile" cli argument
+func setupMemprofile(memprofileArg string) func() {
+	tlog.Info.Printf("Will write memory profile to %q", memprofileArg)
+	f, err := os.Create(memprofileArg)
+	if err != nil {
+		tlog.Fatal.Println(err)
+		os.Exit(exitcodes.Profiler)
+	}
+	exiting := false
+	// Write the memory profile to disk every 60 seconds to get the in-use
+	// memory stats.
+	go func() {
+		for {
+			time.Sleep(60 * time.Second)
+			if exiting {
+				return
+			}
+			_, err = f.Seek(0, 0)
+			if err != nil {
+				tlog.Warn.Printf("memprofile: Seek failed: %v", err)
+				return
+			}
+			err = f.Truncate(0)
+			if err != nil {
+				tlog.Warn.Printf("memprofile: Truncate failed: %v", err)
+				return
+			}
+			err = pprof.WriteHeapProfile(f)
+			if err == nil {
+				tlog.Info.Printf("memprofile: periodic write to %q succeeded",
+					memprofileArg)
+			} else {
+				tlog.Warn.Printf("memprofile: periodic WriteHeapProfile failed: %v", err)
+				return
+			}
+		}
+	}()
+	// Final write on exit.
+	return func() {
+		exiting = true
+		err = pprof.WriteHeapProfile(f)
+		if err != nil {
+			tlog.Warn.Printf("memprofile: on-exit WriteHeapProfile failed: %v", err)
+		}
+		f.Close()
+	}
+}
+
+// setupTrace is called to handle a non-empty "-trace" cli argument
+func setupTrace(traceArg string) func() {
+	tlog.Info.Printf("Writing execution trace to %s", traceArg)
+	f, err := os.Create(traceArg)
+	if err != nil {
+		tlog.Fatal.Println(err)
+		os.Exit(exitcodes.Profiler)
+	}
+	err = trace.Start(f)
+	if err != nil {
+		tlog.Fatal.Println(err)
+		os.Exit(exitcodes.Profiler)
+	}
+	return func() {
+		trace.Stop()
+	}
+}