cmd, core, eth, metrics, p2p: require enabling metrics

metrics/metrics.go

@@ -2,7 +2,9 @@
 package metrics
 
 import (
+	"os"
 	"runtime"
+	"strings"
 	"time"
 
 	"github.com/ethereum/go-ethereum/logger"
@@ -10,9 +12,49 @@ import (
 	"github.com/rcrowley/go-metrics"
 )
 
+// MetricsEnabledFlag is the CLI flag name to use to enable metrics collections.
+var MetricsEnabledFlag = "metrics"
+
+// enabled is the flag specifying if metrics are enable or not.
+var enabled = false
+
+// Init enables or disables the metrics system. Since we need this to run before
+// any other code gets to create meters and timers, we'll actually do an ugly hack
+// and peek into the command line args for the metrics flag.
+func init() {
+	for _, arg := range os.Args {
+		if strings.TrimLeft(arg, "-") == MetricsEnabledFlag {
+			glog.V(logger.Info).Infof("Enabling metrics collection")
+			enabled = true
+		}
+	}
+}
+
+// NewMeter create a new metrics Meter, either a real one of a NOP stub depending
+// on the metrics flag.
+func NewMeter(name string) metrics.Meter {
+	if !enabled {
+		return new(metrics.NilMeter)
+	}
+	return metrics.GetOrRegisterMeter(name, metrics.DefaultRegistry)
+}
+
+// NewTimer create a new metrics Timer, either a real one of a NOP stub depending
+// on the metrics flag.
+func NewTimer(name string) metrics.Timer {
+	if !enabled {
+		return new(metrics.NilTimer)
+	}
+	return metrics.GetOrRegisterTimer(name, metrics.DefaultRegistry)
+}
+
 // CollectProcessMetrics periodically collects various metrics about the running
 // process.
 func CollectProcessMetrics(refresh time.Duration) {
+	// Short circuit if the metrics system is disabled
+	if !enabled {
+		return
+	}
 	// Create the various data collectors
 	memstats := make([]*runtime.MemStats, 2)
 	diskstats := make([]*DiskStats, 2)