I believe that 'writing' (without syncronization) to a TWinControl from a thread or dll function is BAD(tm), but just wondering if the same applies to 'reading' (properties / etc) ?

another way - can 'non-mainthread' access to WinControls be considered 'ReadOnly'

Thanks - SteveG

In general: no
Apply the normal multithreading rules. You have to make sure the main thread does not write at the same time.

Mattias

I would not dare to consider reading from GUI Objects to be thread safe. While _some_ properties supposedly are just variables that can be read at any time some others (e.g. the Canvas' Pixel array) trigger very complex function when read. These supposedly are not thread-read safe and maybe will result in a crash when abused.

-Michael