cgo: make libclang code thread-safe

loader/libclang.go

@@ -21,7 +21,8 @@ int tinygo_clang_visitor(CXCursor c, CXCursor parent, CXClientData client_data);
 */
 import "C"
 
-var globalFileInfo *fileInfo
+// refMap stores references to types, used for clang_visitChildren.
+var refMap RefMap
 
 var diagnosticSeverity = [...]string{
 	C.CXDiagnostic_Ignored: "ignored",
@@ -119,25 +120,17 @@ func (info *fileInfo) parseFragment(fragment string, cflags []string, posFilenam
 		return errs
 	}
 
-	if globalFileInfo != nil {
+	ref := refMap.Put(info)
-		// There is a race condition here but that doesn't really matter as it
+	defer refMap.Remove(ref)
-		// is a sanity check anyway.
-		panic("libclang.go cannot be used concurrently yet")
-	}
-	globalFileInfo = info
-	defer func() {
-		globalFileInfo = nil
-	}()
-
 	cursor := C.clang_getTranslationUnitCursor(unit)
-	C.clang_visitChildren(cursor, (*[0]byte)(unsafe.Pointer(C.tinygo_clang_visitor)), C.CXClientData(uintptr(0)))
+	C.clang_visitChildren(cursor, C.CXCursorVisitor(C.tinygo_clang_visitor), C.CXClientData(ref))
 
 	return nil
 }
 
 //export tinygo_clang_visitor
 func tinygo_clang_visitor(c, parent C.CXCursor, client_data C.CXClientData) C.int {
-	info := globalFileInfo
+	info := refMap.Get(unsafe.Pointer(client_data)).(*fileInfo)
 	kind := C.clang_getCursorKind(c)
 	switch kind {
 	case C.CXCursor_FunctionDecl:

loader/sync.go

@@ -0,0 +1,46 @@
+package loader
+
+import (
+	"sync"
+	"unsafe"
+)
+
+// #include <stdlib.h>
+import "C"
+
+// RefMap is a convenient way to store opaque references that can be passed to
+// C. It is useful if an API uses function pointers and you cannot pass a Go
+// pointer but only a C pointer.
+type RefMap struct {
+	refs map[unsafe.Pointer]interface{}
+	lock sync.Mutex
+}
+
+// Put stores a value in the map. It can later be retrieved using Get. It must
+// be removed using Remove to avoid memory leaks.
+func (m *RefMap) Put(v interface{}) unsafe.Pointer {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	if m.refs == nil {
+		m.refs = make(map[unsafe.Pointer]interface{}, 1)
+	}
+	ref := C.malloc(1)
+	m.refs[ref] = v
+	return ref
+}
+
+// Get returns a stored value previously inserted with Put. Use the same
+// reference as you got from Put.
+func (m *RefMap) Get(ref unsafe.Pointer) interface{} {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	return m.refs[ref]
+}
+
+// Remove deletes a single reference from the map.
+func (m *RefMap) Remove(ref unsafe.Pointer) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+	delete(m.refs, ref)
+	C.free(ref)
+}