void* pointers get corrupted: D bug or misunderstanding?

[Federico Santamorena]

On Sunday, 28 July 2019 at 18:37:26 UTC, Dennis wrote:
> On Sunday, 28 July 2019 at 18:32:24 UTC, Federico Santamorena 
> wrote:
>> So the problem I am noticing is very simple: as you may know 
>> GTK callbacks have a void* user_data argument, what happens, 
>> is that if the flow of code is this: D => C => D the void* 
>> pointer when reaching the third step and finally emerging to 
>> the D language will change its value and get corrupted.
>
> Can you give your exact callback function definition? I once 
> had my context pointer corrupted because I marked my callback 
> extern(C) instead of extern(Windows). Maybe you also have an 
> error in your definition somewhere.

It's a bit complex but:


context is a pointer to a D struct
extern(C) void gtk_search_changed(GtkEditable* widget, void* 
data) { //body }
context.search_input.g_signal_connect("changed", 
&gtk_search_changed, context);

Then inside gtk_search_changed, startCrawling gets called and 
context is just passed to it as the last argument:

DrillContext* startCrawling(in const(DrillConfig) config,
                                    in immutable(string) 
searchValue,
                                    in immutable(void 
function(immutable(FileInfo) result, void* userObject)) 
resultCallback,
                                    in void* userObject) { //body }

And gets called like this:
startCrawling(drillConfig, searchString, &resultFound, context);


Then when the resultCallback gets called its userObject (that now 
should be a pointer to context) is now corrupt:

void resultFound(immutable(FileInfo) result, void* userObject) { 
//body}

And now inside resultFound the void* is completely corrupt