Deadlock: if the callback on Each panics and the app has a recovery, this will ensure that the thread-safe set is left in a usable state by ensuring the read lock is Unlocked. This also has a minor tweak on ToSlice to ensure the capacity hint is correct

Author: deckarep

threadsafe.go

@@ -208,12 +208,12 @@ func (t *threadSafeSet[T]) Cardinality() int {
 
 func (t *threadSafeSet[T]) Each(cb func(T) bool) {
 	t.RLock()
+	defer t.RUnlock()
 	for elem := range *t.uss {
 		if cb(elem) {
 			break
 		}
 	}
-	t.RUnlock()
 }
 
 func (t *threadSafeSet[T]) Iter() <-chan T {
@@ -286,8 +286,9 @@ func (t *threadSafeSet[T]) Pop() (T, bool) {
 }
 
 func (t *threadSafeSet[T]) ToSlice() []T {
-	keys := make([]T, 0, t.Cardinality())
 	t.RLock()
+	l := len(*t.uss)
+	keys := make([]T, 0, l)
 	for elem := range *t.uss {
 		keys = append(keys, elem)
 	}

threadsafe_test.go

@@ -27,6 +27,7 @@ package mapset
 
 import (
 	"encoding/json"
+	"fmt"
 	"math/rand"
 	"runtime"
 	"sync"
@@ -636,3 +637,50 @@ func Test_MarshalJSON(t *testing.T) {
 		t.Errorf("Expected no difference, got: %v", expected.Difference(actual))
 	}
 }
+
+// Test_DeadlockOnEachCallbackWhenPanic ensures that should a panic occur within the context
+// of the Each callback, progress can still be made on recovery. This is an edge case
+// that was called out on issue: https://github.com/deckarep/golang-set/issues/163.
+func Test_DeadlockOnEachCallbackWhenPanic(t *testing.T) {
+	numbers := []int{1, 2, 3, 4}
+	widgets := NewSet[*int]()
+	widgets.Append(&numbers[0], &numbers[1], nil, &numbers[2])
+
+	var panicOccured = false
+
+	doWork := func(s Set[*int]) (err error) {
+		defer func() {
+			if r := recover(); r != nil {
+				panicOccured = true
+				err = fmt.Errorf("failed to print IDs: panicked: %v", r)
+			}
+		}()
+
+		s.Each(func(n *int) bool {
+			// NOTE: this will throw a panic once we get to the nil element.
+			result := *n * 2
+			fmt.Println("result is dereferenced doubled:", result)
+			return false
+		})
+
+		return nil
+	}
+
+	card := widgets.Cardinality()
+	if widgets.Cardinality() != 4 {
+		t.Errorf("Expected widgets to have 4 elements, but has %d", card)
+	}
+
+	doWork(widgets)
+
+	if !panicOccured {
+		t.Error("Expected a panic to occur followed by recover for test to be valid")
+	}
+
+	widgets.Add(&numbers[3])
+
+	card = widgets.Cardinality()
+	if widgets.Cardinality() != 5 {
+		t.Errorf("Expected widgets to have 5 elements, but has %d", card)
+	}
+}