fix: Safe slice mutation during iteration

Mutating the slice while iterating
leads to nasty side effects as the
loop keeps evaluating the original
slice header so removals don't shrink
the loop bounds.

Author: rabbitstack

internal/etw/processors/fs_windows.go

@@ -20,6 +20,9 @@ package processors
 
 import (
 	"expvar"
+	"sync"
+	"time"
+
 	"github.com/rabbitstack/fibratus/pkg/config"
 	"github.com/rabbitstack/fibratus/pkg/event"
 	"github.com/rabbitstack/fibratus/pkg/event/params"
@@ -31,8 +34,6 @@ import (
 	"github.com/rabbitstack/fibratus/pkg/util/va"
 	"golang.org/x/sys/windows"
 	"golang.org/x/time/rate"
-	"sync"
-	"time"
 )
 
 var (
@@ -371,11 +372,13 @@ func (f *fsProcessor) purge() {
 
 			// evict unmatched stack traces
 			for id, q := range f.buckets {
-				for i, evt := range q {
-					if time.Since(evt.Timestamp) > time.Second*30 {
-						f.buckets[id] = append(q[:i], q[i+1:]...)
+				s := q[:0]
+				for _, evt := range q {
+					if time.Since(evt.Timestamp) <= time.Second*30 {
+						s = append(s, evt)
 					}
 				}
+				f.buckets[id] = s
 			}
 
 			f.mu.Unlock()

pkg/event/stackwalk.go

@@ -160,8 +160,9 @@ func (s *StackwalkDecorator) Pop(e *Event) *Event {
 				if !proc.IsCreateProcess() && proc.Params.MustGetPid() != pid {
 					continue
 				}
-				s.buckets[ev.StackID()] = append(qu[:i], qu[i+1:]...)
+				qu = append(qu[:i], qu[i+1:]...)
 			}
+			s.buckets[ev.StackID()] = qu
 		}
 	}
 
@@ -209,16 +210,18 @@ func (s *StackwalkDecorator) flush() []error {
 	errs := make([]error, 0)
 
 	for id, q := range s.buckets {
-		for i, evt := range q {
+		n := q[:0]
+		for _, evt := range q {
 			if time.Since(evt.Timestamp) < maxQueueTTLPeriod {
+				n = append(n, evt)
 				continue
 			}
+
 			stackwalkFlushes.Add(1)
 			err := s.q.push(evt)
 			if err != nil {
 				errs = append(errs, err)
 			}
-			s.buckets[id] = append(q[:i], q[i+1:]...)
 			if stackwalkEnqueued.Value() > 0 {
 				stackwalkEnqueued.Add(-1)
 			}
@@ -227,6 +230,7 @@ func (s *StackwalkDecorator) flush() []error {
 			}
 			stackwalkFlushesEvents.Add(evt.Name, 1)
 		}
+		s.buckets[id] = n
 	}
 
 	return errs