fix: AnalyzeTypeAddr using sync.Once (#531)

Author: sunadoi

internal/runtime/type.go

@@ -2,6 +2,7 @@ package runtime
 
 import (
 	"reflect"
+	"sync"
 	"unsafe"
 )
 
@@ -23,8 +24,8 @@ type TypeAddr struct {
 }
 
 var (
-	typeAddr        *TypeAddr
-	alreadyAnalyzed bool
+	typeAddr *TypeAddr
+	once     sync.Once
 )
 
 //go:linkname typelinks reflect.typelinks
@@ -34,67 +35,64 @@ func typelinks() ([]unsafe.Pointer, [][]int32)
 func rtypeOff(unsafe.Pointer, int32) unsafe.Pointer
 
 func AnalyzeTypeAddr() *TypeAddr {
-	defer func() {
-		alreadyAnalyzed = true
-	}()
-	if alreadyAnalyzed {
-		return typeAddr
-	}
-	sections, offsets := typelinks()
-	if len(sections) != 1 {
-		return nil
-	}
-	if len(offsets) != 1 {
-		return nil
-	}
-	section := sections[0]
-	offset := offsets[0]
-	var (
-		min         uintptr = uintptr(^uint(0))
-		max         uintptr = 0
-		isAligned64         = true
-		isAligned32         = true
-	)
-	for i := 0; i < len(offset); i++ {
-		typ := (*Type)(rtypeOff(section, offset[i]))
-		addr := uintptr(unsafe.Pointer(typ))
-		if min > addr {
-			min = addr
+	once.Do(func() {
+		sections, offsets := typelinks()
+		if len(sections) != 1 {
+			return
 		}
-		if max < addr {
-			max = addr
+		if len(offsets) != 1 {
+			return
 		}
-		if typ.Kind() == reflect.Ptr {
-			addr = uintptr(unsafe.Pointer(typ.Elem()))
+		section := sections[0]
+		offset := offsets[0]
+		var (
+			min         uintptr = uintptr(^uint(0))
+			max         uintptr = 0
+			isAligned64         = true
+			isAligned32         = true
+		)
+		for i := 0; i < len(offset); i++ {
+			typ := (*Type)(rtypeOff(section, offset[i]))
+			addr := uintptr(unsafe.Pointer(typ))
 			if min > addr {
 				min = addr
 			}
 			if max < addr {
 				max = addr
 			}
+			if typ.Kind() == reflect.Ptr {
+				addr = uintptr(unsafe.Pointer(typ.Elem()))
+				if min > addr {
+					min = addr
+				}
+				if max < addr {
+					max = addr
+				}
+			}
+			isAligned64 = isAligned64 && (addr-min)&63 == 0
+			isAligned32 = isAligned32 && (addr-min)&31 == 0
+		}
+		addrRange := max - min
+		if addrRange == 0 {
+			return
+		}
+		var addrShift uintptr
+		if isAligned64 {
+			addrShift = 6
+		} else if isAligned32 {
+			addrShift = 5
 		}
-		isAligned64 = isAligned64 && (addr-min)&63 == 0
-		isAligned32 = isAligned32 && (addr-min)&31 == 0
-	}
-	addrRange := max - min
-	if addrRange == 0 {
-		return nil
-	}
-	var addrShift uintptr
-	if isAligned64 {
-		addrShift = 6
-	} else if isAligned32 {
-		addrShift = 5
-	}
-	cacheSize := addrRange >> addrShift
-	if cacheSize > maxAcceptableTypeAddrRange {
-		return nil
-	}
-	typeAddr = &TypeAddr{
-		BaseTypeAddr: min,
-		MaxTypeAddr:  max,
-		AddrRange:    addrRange,
-		AddrShift:    addrShift,
-	}
+		cacheSize := addrRange >> addrShift
+		if cacheSize > maxAcceptableTypeAddrRange {
+			return
+		}
+		typeAddr = &TypeAddr{
+			BaseTypeAddr: min,
+			MaxTypeAddr:  max,
+			AddrRange:    addrRange,
+			AddrShift:    addrShift,
+		}
+	})
+
 	return typeAddr
 }