[Lazarus] TThread.WaitFor blocks the main event loop under Linux

[Luca Olivetti]

En/na Michael Van Canneyt ha escrit:

> 
> and in "WaitFor" it says:
> 
> "Call WaitFor to obtain the value of ReturnValue when the
> thread finishes executing. WaitFor doesn't return until the thread
> terminates, so the thread must exit either by finishing the Execute method
> or by exiting when the Terminated property is true."
> 
> There you have it. Nowhere does it say that if the main thread is blocked,
> your synchronize() method will be executed nonetheless. Indeed, both specs
> explicitly say that the calling thread is suspended or blocked (!) till 
> the call returns.


And in older versions of the documentation (delphi 2) it explicitly says

"Don't call WaitFor in the context of the main VCL thread if your thread 
uses Synchronize. Doing so will either cause a deadlock, making it 
appear that your application has hung, or cause an EThread exception to 
be raised. (Synchronize waits for the main VCL thread to enter the 
message loop before allowing the method it is trying to synchronize to 
execute. If the main VCL thread has called WaitFor, it won't enter the 
message loop and Synchronize will never return. TThread detects that 
case and will raise an EThread exception in the thread, causing it to 
terminate and, if not caught in the Execute method, the application will 
terminate as well. If Synchronize is already waiting on the main VCL 
thread when WaitFor is called, TThread can't intervene, and your 
application will deadlock.)"

They probably changed the implementation later on to avoid this, but old 
farts like me still avoid to mix synchronize and waitfor.

Bye
-- 
Luca Olivetti
Wetron Automatización S.A. http://www.wetron.es/
Tel. +34 93 5883004 (Ext.133)  Fax +34 93 5883007