Merge lp:~widelands-dev/widelands/bug-1815277-persistence-memory-leak into lp:widelands

[GunChleoc]

Fix a memory leak in persistence.cc

There is still a second leak on the same line that I didn't manage to fix.

[bunnybot (widelandsofficial)]

Continuous integration builds have changed state:

Travis build 4455. State: passed. Details: https://travis-ci.org/widelands/widelands/builds/491524355.
Appveyor build 4243. State: success. Details: https://ci.appveyor.com/project/widelands-dev/widelands/build/_widelands_dev_widelands_bug_1815277_persistence_memory_leak-4243.

[Notabilis (notabilis27)]

I was able to reproduce the memory leak of the bug report but I wasn't able to observe a change by this branch. Both times I loaded the same autosave single player game of Autocrat and got the same leak-message (except for the memory addresses). Should something change in the output?

I am also unsure whether your change really changes anything. As far as I know, a reference is basically another way to write a pointer, so no memory release is done by your code. But maybe I am wrong about this.

From the call stack and some digging through the eris code (that I don't really understand) it seems to me as if the leak is / might be in the u_closure() function deep within the eris code. Do we fix third-party leaks or do we just ignore them?

[GunChleoc (gunchleoc)]

I got 2 leak entries previously, going through the same line in persistence.cc. Now I'm only getting 1.

Ma C is not good enough for me to touch Eris, but if you can fix it, we could contribute our fix to the eris project as well.

[Notabilis (notabilis27)]

It seems as if I was wrong about my assumption regarding the Eris function, its garbage collector should clean everything up. But I will do some more digging, maybe I can figure out where the leak is.

If this branch makes it better for you, I have no objection to merging it.

[GunChleoc (gunchleoc)]

OK, let's have it and leave the bug open.

@bunnybot merge

=== modified file 'src/scripting/persistence.cc'
--- src/scripting/persistence.cc	2018-04-07 16:59:00 +0000
+++ src/scripting/persistence.cc	2019-02-11 08:25:08 +0000
@@ -48,10 +48,10 @@
 }
 
 const char* LuaReader(lua_State* /* L */, void* userdata, size_t* bytes_read) {
-	LuaReaderHelper* helper = static_cast<LuaReaderHelper*>(userdata);
+	const LuaReaderHelper& helper = *static_cast<LuaReaderHelper*>(userdata);
 
-	*bytes_read = helper->data_len;
-	return helper->data.get();
+	*bytes_read = helper.data_len;
+	return helper.data.get();
 }
 
 }  // namespace