Release GIL in function generator

Signed-off-by: Oleksii Moskalenko <moskalenko.alexey@gmail.com>

Author: pyalex

bind/gen_func.go

@@ -260,6 +260,14 @@ func (g *pyGen) genFuncBody(sym *symbol, fsym *Func) {
 			}
 		}
 	}
+
+	// release GIL
+	g.gofile.Printf("_saved_thread := C.PyEval_SaveThread()\n")
+	if !rvIsErr && nres != 2 {
+		// reacquire GIL after return
+		g.gofile.Printf("defer C.PyEval_RestoreThread(_saved_thread)\n")
+	}
+
 	if isMethod {
 		g.gofile.Printf(
 			`vifc, __err := gopyh.VarFromHandleTry((gopyh.CGoHandle)(_handle), "%s")
@@ -407,6 +415,9 @@ if __err != nil {
 
 	if rvIsErr || nres == 2 {
 		g.gofile.Printf("\n")
+		// reacquire GIL
+		g.gofile.Printf("C.PyEval_RestoreThread(_saved_thread)\n")
+
 		g.gofile.Printf("if __err != nil {\n")
 		g.gofile.Indent()
 		g.gofile.Printf("estr := C.CString(__err.Error())\n")