DLL Instances Threads etc.

[Fred Oxenby]

I seem not to be able to get this right.
This is the plot.

PROGRAM loads an RUNTIME DLL
   When loaded RUNTIME checks if PROGRAM has an valid INI-file
   If not PROGRAM will not start.
PROGRAM Initialize RUNTIME with diverse GLOBAL assignments.
PROGRAM calls a function in WORKER1 DLL
   WORKER1 starts a new Thread and returns to PROGRAM
   WORKER1 Thread calls functions in RUNTIME
PROGRAM calls a function in  WORKER2 DLL
   WORKER2 starts a new Thread and returns to PROGRAM
   WORKER2 Thread calls functions in RUNTIME
PROGRAM calls a function in  WORKER3 DLL
   WORKER3 starts a new Thread and returns to PROGRAM
   WORKER3 Thread calls functions in RUNTIME
   WORKER3 Thread calls a function in WORKER2 witch calls a function in RUNTIME 
Etcetera...
For the record...
   Globals in RUNTIME is static, ie they are not changed by
   WORKER(S)
The Question:
   All this Globals as initialised by PROGRAM
   are they ALWAYS seen with their initialised value by any thread in WORKER DLL-s?

Thanks for your help


-------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se



[This message has been edited by Fred Oxenby (edited February 26, 2000).]

[Fred Oxenby]

Also for the record:
a GLOBAL in a DLL is LOCAL to the DLL, so I am not asking
if a global in RUNTIME can be accessed from WORKER or another
part of the code not belonging to RUNTIME


------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

[Lance Edmonds]

STATIC/GLOBAL variables in subs/functions are seen by all threads in the process that call them. In other words, if you have a sub in PROGRAM that alters any global/static variable and that sub is called from a thread, then the code is not threadsafe...

When changing any variable that can be read and changed by other threads, you must use a CRITICALSECTION or some other synchronization technique to ensure that the data is not partially updated while being read by another thread during a context-switch.

Michael Mattias wrote an article (recently in Basically Speaking magazine) on synchronization... it give you a basic idea, but does not really cover allocating and managing Thread Local Storage, or TLS as it is known. (Hint hint!)

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>