[Lazarus] thread safe

[Hans-Peter Diettrich]

Mattias Gaertner schrieb:

> Whether a function is "thread safe" does not depend on how you call it.
> If a function can fail if it is called with wrong parameters or by the
> wrong Thread, then it is as Reimar wrote: it is not thread safe.

I dare to disagree. When a procedure call can fail in a single-threaded 
environment, for some reason, then it is allowed to fail in a 
multi-threaded environment as well. It's up to the function to return an 
appropriate error code - this doesn't make the procedure thread-unsafe.

> And now follows a lot of text, how to safely call not thread safe
> functions, which might have been useful on a forum for parallel
> programming, if it would not invent misleading terms like "completely
> thread safe"

That's why I'd classify procedures as *immanently* thread-safe, when 
they don't rely on unsafe shared data (objects...), or as protected 
against *certain* threading issues. The rest will stay "unknown", or can 
have a list of *known* threading (or reentrancy...) issues.

Objects are much harder to classify, because only few of them are 
designed with only thread-safe public methods. Nonetheless it would be 
interesting to know, which objects (classes) can be used safely when 
*encapsulated* in an thread [created by the thread, no references passed 
to or ending up in other threads]. Obviously all event handlers and 
other notification callbacks, stored in an object, can violate this 
requirement.

DoDi