Enable profiling options when 'pprof' tag is set (#2813)

This commit enables cpu, mem, block, and mutex profling of the FZF
executable. To support flushing the profiles at program exit it adds
util.AtExit to register "at exit" functions and mandates that util.Exit
is used instead of os.Exit to stop the program.

Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>

src/options.go

@@ -363,6 +363,10 @@ type Options struct {
 	WalkerRoot   string
 	WalkerSkip   []string
 	Version      bool
+	CPUProfile   string
+	MEMProfile   string
+	BlockProfile string
+	MutexProfile string
 }
 
 func filterNonEmpty(input []string) []string {
@@ -454,14 +458,14 @@ func defaultOptions() *Options {
 
 func help(code int) {
 	os.Stdout.WriteString(usage)
-	os.Exit(code)
+	util.Exit(code)
 }
 
 var errorContext = ""
 
 func errorExit(msg string) {
 	os.Stderr.WriteString(errorContext + msg + "\n")
-	os.Exit(exitError)
+	util.Exit(exitError)
 }
 
 func optString(arg string, prefixes ...string) (bool, string) {
@@ -1978,6 +1982,14 @@ func parseOptions(opts *Options, allArgs []string) {
 			opts.WalkerSkip = filterNonEmpty(strings.Split(nextString(allArgs, &i, "directory names to ignore required"), ","))
 		case "--version":
 			opts.Version = true
+		case "--profile-cpu":
+			opts.CPUProfile = nextString(allArgs, &i, "file path required: cpu")
+		case "--profile-mem":
+			opts.MEMProfile = nextString(allArgs, &i, "file path required: mem")
+		case "--profile-block":
+			opts.BlockProfile = nextString(allArgs, &i, "file path required: block")
+		case "--profile-mutex":
+			opts.MutexProfile = nextString(allArgs, &i, "file path required: mutex")
 		case "--":
 			// Ignored
 		default:
@@ -2303,6 +2315,11 @@ func ParseOptions() *Options {
 	errorContext = ""
 	parseOptions(opts, os.Args[1:])
 
+	if err := opts.initProfiling(); err != nil {
+		errorExit("failed to start pprof profiles: " + err.Error())
+	}
+
 	postProcessOptions(opts)
+
 	return opts
 }