Add RegexLeakHandler to allow callers to supply a custom leak handler

regex.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"fmt"
 	"runtime"
+	"sync/atomic"
 	"unicode/utf16"
 
 	"github.com/tetratelabs/wazero/api"
@@ -63,7 +64,28 @@ var (
 )
 
 // ShouldPanic determines whether the finalizer will panic if it finds a Regex that has not been closed.
-var ShouldPanic bool = true
+var ShouldPanic = true
+
+// RegexLeakHandler is a callback function that will be invoked if a finalizer is called for a Regex that has not
+// been closed. This allows applications to provide custom handling logic beyond panicing if a Regex leak is detected.
+var regexLeakHandler atomic.Value
+
+// SetRegexLeakHandler sets a |handler| function to be executed if a finalizer is called for a Regex instance that
+// has not been properly closed through it's Close() method. Note that if a custom leak handler function is provided,
+// the ShouldPanic variable will be ignored and the code will not panic if a Regex leak is detected.
+func SetRegexLeakHandler(handler func()) {
+	regexLeakHandler.Store(handler)
+}
+
+// getRegexLeakHandler returns the custom handler function set by SetRegexLeakHandler, or nil if no custom handler has
+// been set.
+func getRegexLeakHandler() func() {
+	val := regexLeakHandler.Load()
+	if val == nil {
+		return nil
+	}
+	return val.(func())
+}
 
 // RegexFlags are flags to define the behavior of the regular expression. Use OR (|) to combine flags. All flag values
 // were taken directly from ICU.
@@ -171,8 +193,13 @@ func CreateRegex(stringBufferInBytes uint32) Regex {
 	// by GC, this finalizer ensures that regexes are being used as efficiently as possible by maximizing pool rotations.
 	// Hopefully, this would be caught during development and not in production.
 	runtime.SetFinalizer(pr, func(pr *privateRegex) {
-		if pr.mod != nil && ShouldPanic {
-			panic("Finalizer found a Regex that was never closed")
+		if pr.mod != nil {
+			if leakHandler := getRegexLeakHandler(); leakHandler != nil {
+				leakHandler()
+			} else if ShouldPanic {
+				panic("Finalizer found a Regex that was never closed")
+			}
+			_ = pr.Close()
 		}
 	})
 	return pr

regex_test.go

@@ -16,7 +16,10 @@ package regex
 
 import (
 	"context"
+	"runtime"
+	"sync/atomic"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 )
@@ -187,3 +190,29 @@ func TestRegexSubstring(t *testing.T) {
 	require.Equal(t, "ghx", substr)
 	require.NoError(t, regex.Close())
 }
+
+// TestRegexLeakHandler asserts that RegexLeakHandler is invoked when a regex is not closed before
+// it gets garbage collected.
+func TestRegexLeakHandler(t *testing.T) {
+	leakHandlerCalled := atomic.Bool{}
+
+	SetRegexLeakHandler(func() {
+		leakHandlerCalled.Store(true)
+	})
+	defer func() {
+		SetRegexLeakHandler(nil)
+	}()
+
+	regex := CreateRegex(1024)
+	regex.Close()
+	regex = nil
+	runtime.GC()
+	time.Sleep(500 * time.Millisecond)
+	require.False(t, leakHandlerCalled.Load())
+
+	regex = CreateRegex(1024)
+	regex = nil
+	runtime.GC()
+	time.Sleep(500 * time.Millisecond)
+	require.True(t, leakHandlerCalled.Load())
+}