Stowage/godot
2
0
Fork 0
mirror of https://github.com/godotengine/godot.git synced 2025-11-01 06:01:14 +00:00
Code Issues Projects Releases Packages Wiki Activity

Fix dangling and reassigned Variants

Browse source 
This commit addresses multiple issues with `Variant`s that point to an `Object`
which is later released, when it's tried to be accessed again.

Formerly, **while running on the debugger the system would check if the instance id was
still valid** to print warnings or return special values. Some cases weren't being
warned about whatsoever.

Also, a newly allocated `Object` could happen to be allocated at the same memory
address of an old one, making cases of use hard to find and having **`Variant`s pointing
to the old one magically reassigned to the new**.

This commit makes the engine realize all these situations **under debugging**
so you can detect and fix them. Running without a debugger attached will still
behave as it always did.

Also the warning messages have been extended and made clearer.

All that said, in the name of performance there's still one possible case of undefined
behavior: in multithreaded scripts there would be a race condition between a thread freeing
an `Object` and another one trying to operate on it. The latter may not realize the
`Object` has been freed soon enough. But that's a case of bad scripting that was never
supported anyway.
This commit is contained in:
Pedro J. Estébanez 2020-04-23 12:40:06 +02:00
parent 07c4dc1b30
commit d904d05e65
8 changed files with 378 additions and 166 deletions
Download patch file Download diff file Expand all files Collapse all files

44
core/object.cpp
View file

@ -33,6 +33,7 @@
#include "core/class_db.h"
#include "core/core_string_names.h"
#include "core/message_queue.h"
#include "core/object_rc.h"
#include "core/os/os.h"
#include "core/print_string.h"
#include "core/resource.h"
@ -968,6 +969,37 @@ void Object::cancel_delete() {
_predelete_ok = true;
}
#ifdef DEBUG_ENABLED
ObjectRC *Object::_use_rc() {
// The RC object is lazily created the first time it's requested;
// that way, there's no need to allocate and release it at all if this Object
// is not being referred by any Variant at all.
// Although when dealing with Objects from multiple threads some locking
// mechanism should be used, this at least makes safe the case of first
// assignment.
ObjectRC *rc = nullptr;
ObjectRC *const creating = reinterpret_cast<ObjectRC *>(1);
if (unlikely(_rc.compare_exchange_strong(rc, creating, std::memory_order_acq_rel))) {
// Not created yet
rc = memnew(ObjectRC(this));
_rc.store(rc, std::memory_order_release);
return rc;
}
// Spin-wait until we know it's created (or just return if it's already created)
for (;;) {
if (likely(rc != creating)) {
rc->increment();
return rc;
}
rc = _rc.load(std::memory_order_acquire);
}
}
#endif
void Object::set_script_and_instance(const RefPtr &p_script, ScriptInstance *p_instance) {
//this function is not meant to be used in any of these ways
@ -1944,6 +1976,9 @@ Object::Object() {
instance_binding_count = 0;
memset(_script_instance_bindings, 0, sizeof(void *) * MAX_SCRIPT_INSTANCE_BINDINGS);
script_instance = NULL;
#ifdef DEBUG_ENABLED
_rc.store(nullptr, std::memory_order_release);
#endif
#ifdef TOOLS_ENABLED
_edited = false;
@ -1957,6 +1992,15 @@ Object::Object() {
Object::~Object() {
#ifdef DEBUG_ENABLED
ObjectRC *rc = _rc.load(std::memory_order_acquire);
if (rc) {
if (rc->invalidate()) {
memfree(rc);
}
}
#endif
if (script_instance)
memdelete(script_instance);
script_instance = NULL;