Replaced cpu directive with command line flag

config/config.go

@@ -47,9 +47,6 @@ type Config struct {
 	// these are executed in response to SIGINT and are blocking
 	Shutdown []func() error
 
-	// MaxCPU is the maximum number of cores for the whole process to use
-	MaxCPU int
-
 	// The path to the configuration file from which this was loaded
 	ConfigFile string
 }

config/directives.go

@@ -3,9 +3,6 @@ package config
 import (
 	"os"
 	"os/exec"
-	"runtime"
-	"strconv"
-	"strings"
 
 	"github.com/mholt/caddy/middleware"
 )
@@ -74,46 +71,6 @@ func init() {
 			p.cfg.TLS = tls
 			return nil
 		},
-		"cpu": func(p *parser) error {
-			sysCores := runtime.NumCPU()
-
-			if !p.nextArg() {
-				return p.argErr()
-			}
-			strNum := p.tkn()
-
-			setCPU := func(val int) {
-				if val < 1 {
-					val = 1
-				}
-				if val > sysCores {
-					val = sysCores
-				}
-				if val > p.cfg.MaxCPU {
-					p.cfg.MaxCPU = val
-				}
-			}
-
-			if strings.HasSuffix(strNum, "%") {
-				// Percent
-				var percent float32
-				pctStr := strNum[:len(strNum)-1]
-				pctInt, err := strconv.Atoi(pctStr)
-				if err != nil || pctInt < 1 || pctInt > 100 {
-					return p.err("Parse", "Invalid number '"+strNum+"' (must be a positive percentage between 1 and 100)")
-				}
-				percent = float32(pctInt) / 100
-				setCPU(int(float32(sysCores) * percent))
-			} else {
-				// Number
-				num, err := strconv.Atoi(strNum)
-				if err != nil || num < 0 {
-					return p.err("Parse", "Invalid number '"+strNum+"' (requires positive integer or percent)")
-				}
-				setCPU(num)
-			}
-			return nil
-		},
 		"startup": func(p *parser) error {
 			// TODO: This code is duplicated with the shutdown directive below
 

main.go

 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"log"
 	"net"
+	"runtime"
+	"strconv"
+	"strings"
 	"sync"
 
 	"github.com/mholt/caddy/config"
@@ -15,18 +19,26 @@ var (
 	conf  string
 	http2 bool // TODO: temporary flag until http2 is standard
 	quiet bool
+	cpu   string
 )
 
 func init() {
 	flag.StringVar(&conf, "conf", config.DefaultConfigFile, "the configuration file to use")
 	flag.BoolVar(&http2, "http2", true, "enable HTTP/2 support") // TODO: temporary flag until http2 merged into std lib
 	flag.BoolVar(&quiet, "quiet", false, "quiet mode (no initialization output)")
+	flag.StringVar(&cpu, "cpu", "100%", "CPU cap")
 	flag.Parse()
 }
 
 func main() {
 	var wg sync.WaitGroup
 
+	// Set CPU cap
+	err := setCPU(cpu)
+	if err != nil {
+		log.Fatal(err)
+	}
+
 	// Load config from file
 	allConfigs, err := config.Load(conf)
 	if err != nil {
@@ -109,3 +121,38 @@ func arrangeBindings(allConfigs []config.Config) (map[string][]config.Config, er
 
 	return addresses, nil
 }
+
+// setCPU parses string cpu and sets GOMAXPROCS
+// according to its value. It accepts either
+// a number (e.g. 3) or a percent (e.g. 50%).
+func setCPU(cpu string) error {
+	var numCPU int
+
+	availCPU := runtime.NumCPU()
+
+	if strings.HasSuffix(cpu, "%") {
+		// Percent
+		var percent float32
+		pctStr := cpu[:len(cpu)-1]
+		pctInt, err := strconv.Atoi(pctStr)
+		if err != nil || pctInt < 1 || pctInt > 100 {
+			return errors.New("Invalid CPU value: percentage must be between 1-100")
+		}
+		percent = float32(pctInt) / 100
+		numCPU = int(float32(availCPU) * percent)
+	} else {
+		// Number
+		num, err := strconv.Atoi(cpu)
+		if err != nil || num < 1 {
+			return errors.New("Invalid CPU value: provide a number or percent greater than 0")
+		}
+		numCPU = num
+	}
+
+	if numCPU > availCPU {
+		numCPU = availCPU
+	}
+
+	runtime.GOMAXPROCS(numCPU)
+	return nil
+}

server/server.go

@@ -11,7 +11,6 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
-	"runtime"
 
 	"github.com/bradfitz/http2"
 	"github.com/mholt/caddy/config"
@@ -41,11 +40,6 @@ func New(addr string, configs []config.Config, tls bool) (*Server, error) {
 			return nil, fmt.Errorf("Cannot serve %s - host already defined for address %s", conf.Address(), s.address)
 		}
 
-		// Use all CPUs (if needed) by default
-		if conf.MaxCPU == 0 {
-			conf.MaxCPU = runtime.NumCPU()
-		}
-
 		vh := virtualHost{config: conf}
 
 		// Build middleware stack
@@ -73,7 +67,7 @@ func (s *Server) Serve() error {
 	}
 
 	for _, vh := range s.vhosts {
-		// Execute startup functions
+		// Execute startup functions now
 		for _, start := range vh.config.Startup {
 			err := start()
 			if err != nil {
@@ -81,13 +75,8 @@ func (s *Server) Serve() error {
 			}
 		}
 
-		// Use highest procs value across all configurations
-		if vh.config.MaxCPU > 0 && vh.config.MaxCPU > runtime.GOMAXPROCS(0) {
-			runtime.GOMAXPROCS(vh.config.MaxCPU)
-		}
-
-		if len(vh.config.Shutdown) > 0 {
 		// Execute shutdown commands on exit
+		if len(vh.config.Shutdown) > 0 {
 			go func() {
 				interrupt := make(chan os.Signal, 1)
 				signal.Notify(interrupt, os.Interrupt, os.Kill) // TODO: syscall.SIGQUIT? (Ctrl+\, Unix-only)