Fix slot call deadlock

vm/src/builtins/type.rs

@@ -667,11 +667,12 @@ impl GetAttr for PyType {
 
         if let Some(ref attr) = mcl_attr {
             let attr_class = attr.class();
-            if attr_class
+            let has_descr_set = attr_class
                 .mro_find_map(|cls| cls.slots.descr_set.load())
-                .is_some()
-            {
-                if let Some(descr_get) = attr_class.mro_find_map(|cls| cls.slots.descr_get.load()) {
+                .is_some();
+            if has_descr_set {
+                let descr_get = attr_class.mro_find_map(|cls| cls.slots.descr_get.load());
+                if let Some(descr_get) = descr_get {
                     let mcl = mcl.into_owned().into();
                     return descr_get(attr.clone(), Some(zelf.to_owned().into()), Some(mcl), vm);
                 }
@@ -681,7 +682,8 @@ impl GetAttr for PyType {
         let zelf_attr = zelf.get_attr(name);
 
         if let Some(ref attr) = zelf_attr {
-            if let Some(descr_get) = attr.class().mro_find_map(|cls| cls.slots.descr_get.load()) {
+            let descr_get = attr.class().mro_find_map(|cls| cls.slots.descr_get.load());
+            if let Some(descr_get) = descr_get {
                 drop(mcl);
                 return descr_get(attr.clone(), None, Some(zelf.to_owned().into()), vm);
             }
@@ -745,7 +747,8 @@ impl Callable for PyType {
             return Ok(obj);
         }
 
-        if let Some(init_method) = obj.class().mro_find_map(|cls| cls.slots.init.load()) {
+        let init = obj.class().mro_find_map(|cls| cls.slots.init.load());
+        if let Some(init_method) = init {
             init_method(obj.clone(), args, vm)?;
         }
         Ok(obj)

vm/src/function/protocol.rs

@@ -84,14 +84,14 @@ where
     T: TryFromObject,
 {
     fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
-        let iterfn;
-        {
+        let iterfn = {
             let cls = obj.class();
-            iterfn = cls.mro_find_map(|x| x.slots.iter.load());
+            let iterfn = cls.mro_find_map(|x| x.slots.iter.load());
             if iterfn.is_none() && !cls.has_attr(identifier!(vm, __getitem__)) {
                 return Err(vm.new_type_error(format!("'{}' object is not iterable", cls.name())));
             }
-        }
+            iterfn
+        };
         Ok(Self {
             iterable: obj,
             iterfn,

vm/src/object/core.rs

@@ -762,7 +762,8 @@ impl PyObject {
         }
 
         // CPython-compatible drop implementation
-        if let Some(slot_del) = self.class().mro_find_map(|cls| cls.slots.del.load()) {
+        let del = self.class().mro_find_map(|cls| cls.slots.del.load());
+        if let Some(slot_del) = del {
             call_slot_del(self, slot_del)?;
         }
         if let Some(wrl) = self.weak_ref_list() {

vm/src/protocol/buffer.rs

@@ -140,7 +140,8 @@ impl PyBuffer {
 impl TryFromBorrowedObject for PyBuffer {
     fn try_from_borrowed_object(vm: &VirtualMachine, obj: &PyObject) -> PyResult<Self> {
         let cls = obj.class();
-        if let Some(f) = cls.mro_find_map(|cls| cls.slots.as_buffer) {
+        let as_buffer = cls.mro_find_map(|cls| cls.slots.as_buffer);
+        if let Some(f) = as_buffer {
             return f(obj, vm);
         }
         Err(vm.new_type_error(format!(

vm/src/protocol/mapping.rs

@@ -146,11 +146,8 @@ impl PyMapping<'_> {
     }
 
     pub fn find_methods(obj: &PyObject, vm: &VirtualMachine) -> Option<&'static PyMappingMethods> {
-        if let Some(f) = obj.class().mro_find_map(|cls| cls.slots.as_mapping.load()) {
-            Some(f(obj, vm))
-        } else {
-            None
-        }
+        let as_mapping = obj.class().mro_find_map(|cls| cls.slots.as_mapping.load());
+        as_mapping.map(|f| f(obj, vm))
     }
 
     pub fn length_opt(&self, vm: &VirtualMachine) -> Option<PyResult<usize>> {

vm/src/protocol/number.rs

@@ -163,9 +163,8 @@ impl<'a> PyNumber<'a> {
 
 impl PyNumber<'_> {
     pub fn find_methods(obj: &PyObject, vm: &VirtualMachine) -> Option<&'static PyNumberMethods> {
-        obj.class()
-            .mro_find_map(|x| x.slots.as_number.load())
-            .map(|f| f(obj, vm))
+        let as_number = obj.class().mro_find_map(|x| x.slots.as_number.load());
+        as_number.map(|f| f(obj, vm))
     }
 
     pub fn methods(&self) -> &'static PyNumberMethods {

vm/src/protocol/sequence.rs

@@ -145,7 +145,8 @@ impl PySequence<'_> {
     pub fn find_methods(obj: &PyObject, vm: &VirtualMachine) -> Option<&'static PySequenceMethods> {
         let cls = obj.class();
         if !cls.is(vm.ctx.types.dict_type) {
-            if let Some(f) = cls.mro_find_map(|x| x.slots.as_sequence.load()) {
+            let as_sequence = cls.mro_find_map(|x| x.slots.as_sequence.load());
+            if let Some(f) = as_sequence {
                 return Some(f(obj, vm));
             }
         }