Use SwapInt64 to snapshot counters (segmentio#441)

Using LoadInt64 and then AddInt64 can lead to incoherent results if snapshot() is called twice at the same time.
huangfu · May 6, 2020 · 2213fc9 · 2213fc9
1 parent e0af1cf
commit 2213fc9
Showing 1 changed file with 1 addition and 4 deletions.
diff --git a/stats.go b/stats.go
@@ -36,10 +36,7 @@ func (c *counter) observe(v int64) {
 }
 
 func (c *counter) snapshot() int64 {
-	p := c.ptr()
-	v := atomic.LoadInt64(p)
-	atomic.AddInt64(p, -v)
-	return v
+	return atomic.SwapInt64(c.ptr(), 0)
 }
 
 // gauge is an atomic integer that may be set to any arbitrary value, the value