Fix ntp collector thread safety (#1014)

Make the ntp collector thread safe by wrapping a mutex lock around the
leapMidnight variable.

Signed-off-by: Ben Kochie <superq@gmail.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/collector/ntp.go b/collector/ntp.go
index 2580353..e545a1d 100644
--- a/collector/ntp.go
+++ b/collector/ntp.go
@@ -18,6 +18,7 @@ package collector
 import (
         "fmt"
         "net"
+        "sync"
         "time"
 
         "github.com/beevik/ntp"
@@ -40,7 +41,8 @@ var (
         ntpMaxDistance     = kingpin.Flag("collector.ntp.max-distance", "Max accumulated distance to the root").Default("3.46608s").Duration()
         ntpOffsetTolerance = kingpin.Flag("collector.ntp.local-offset-tolerance", "Offset between local clock and local ntpd time to tolerate").Default("1ms").Duration()
 
-        leapMidnight time.Time
+        leapMidnight      time.Time
+        leapMidnightMutex = &sync.Mutex{}
 )
 
 type ntpCollector struct {
@@ -143,6 +145,7 @@ func (c *ntpCollector) Update(ch chan<- prometheus.Metric) error {
         // configuration from node_exporter user to the developer.
 
         maxerr := *ntpOffsetTolerance
+        leapMidnightMutex.Lock()
         if resp.Leap == ntp.LeapAddSecond || resp.Leap == ntp.LeapDelSecond {
                 // state of leapMidnight is cached as leap flag is dropped right after midnight
                 leapMidnight = resp.Time.Truncate(hour24).Add(hour24)
@@ -151,6 +154,7 @@ func (c *ntpCollector) Update(ch chan<- prometheus.Metric) error {
                 // tolerate leap smearing
                 maxerr += time.Second
         }
+        leapMidnightMutex.Unlock()
 
         if resp.Validate() == nil && resp.RootDistance <= *ntpMaxDistance && resp.MinError <= maxerr {
                 ch <- c.sanity.mustNewConstMetric(1)