On 08/08/13 11:58, Henry Vermaak wrote:
> On Thu, Aug 08, 2013 at 11:34:53AM +0100, Lukasz Sokol wrote:
>> This would be fine, IFF i was adding this to the main form of my
>> application... but I'm not. I'm trying to wrap this .dll in a
>> separate unit, only communicating to the form through a wrapper
>> object, defined in a separate unit. The object itself, would be
>> created /by/ the form window, but won't be a GUI object, so won't be
>> in the message queue;
>>
>> Doing a chain like:
>>
>> (Setup) (form passes its handle to the object) -> (object installs
>> callback function) and then (normal operation) (form receives callback
>> via Windows Message) -> (form calls e.g OnCallback function of the
>> object)
>>
>> seems a bit backwards.
>>
>> I can imagine, that I need to have the Callback procedure as
>>
>> procedure Callback(Port, Event, Value : Integer); stdcall;
>>
>> but how do I call functions/procedures of MyObject in a threadsafe
>> manner from there?
>
> Lazarus has QueueAsyncCall, which is a thread safe, cross platform way
> of queueing method calls asynchronously.
>
> E.g. for USB hotplug notification, I register this function with my
> device library:
>
> procedure NotifyPlug(status: cint); cdecl;
> begin
> Application.QueueAsyncCall(@MainForm.NotifyAsync, status);
> end;
>
> Henry
Hello Henry,
but I would then need to make the wrapper object aware of the Application
or its forms then?
I wanted the wrapper unit to be as self-contained as much as possible,
(so the callback function is defined in a unit that only has Classes, SysUtils
and dynlibs as uses,
i.e. no Forms. Controls or Graphics)
but still be thread-safe w/r/t to where the wrapper object is created
(within a GUI form or /not/)
Unless I can do:
procedure Callback (...); stdcall;
begin
{Application}.QueueAsyncCall(MyObject.CallbackNotify, ...);
end;
no?
Thanks,
Lukasz
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