[Lazarus] Clipboard.HasFormat(CF_TEXT)

[C Western]

On 26/05/14 14:38, Mattias Gaertner wrote:
> On Mon, 26 May 2014 12:31:41 +0100
> C Western <l at c-m-w.me.uk> wrote:
>
>> I may have discovered an issue with the clipboard on Linux/GTK2. My
>> application updates a paste button and menu item via an action that
>> updates on idle by calling Clipboard.HasFormat(CF_TEXT). Pasting is
>> intermittently failing/hanging for 10 seconds, and I think the issue is
>> that the Clipboard.HasFormat routine is reentered. Clipboard.HasFormat
>> can call Application.ProcessMessages, and a possible failure path seems
>> to be that a Ctrl+V arrives during this call of ProcessMessages, and in
>> handling this Clipboard.HasFormat is called, and the routine seems to
>> have nothing to protect against reentry.
>>
>> Two Ctrl+V's in quick succession could potentially trigger then same
>> issue, if the clipboard contents are large.
>>
>> Have I misunderstood something? I couldn't see anything in the bug
>> tracker about this, though there is a reported issue about large pastes.
>> I can't see any obvious fix at the application level other than leaving
>> the paste items permanently enabled.
>>
>> I think this is not an issue in MS Windows as I don't think the
>> clipboard requires communication with another process.
>
> Can you create a small example?
>

I would think that any application that uses the clipboard would be 
vulnerable to this. For example, I think I can trigger the issue with 
two Ctrl-V's in succession with the edittest example in lazarus. Start 
it and say libre office (I used a spreadsheet with about 1000 lines of 
data.) Select and copy a large block in the spreadsheet, and then hold 
down the Ctrl+v key in edittest. A few copies will appear very quickly, 
but then the application hangs for several seconds (at least). Lazarus 
itself can be made to hang in the same way.

Colin