Thanks for the response.
The library uses a centralised function to start all its threads using
pthread_create. If I can make this central function inform FPC about all
the threads created, would this work?
Assuming it would work: what information would FPC require? When would
this info be required, before or after thread creation? What needs to be
done on the FPC side with this info?
Wimpie
Jonas Maebe wrote:
On 31 Jul 2009, at 19:05, Wimpie Nortje wrote:
I am trying to use a shared lib written in C in my FPC program. The
lib creates a number of threads and requires callbacks into the main
app. It can call the callback from any of the threads.
Calling FPC code from threads not created by FPC does not work at this
time on any unix-like platform.
When I compile without stack checking everything (seems) to work fine
but when stack checking is on I get stack error (error 202) on entry
to the callback function. I can break on the callback's 'begin' and
see valid values for all the function parameters but when I step into
the function body it crashes.
That's because the stack checking has to be initialised per thread and
this is normally done when you create a thread via tthread.create() or
beginthread(). Disable stack checking.
I say 'seems' when not using stack checking because when the app
becomes large I get a lot of strange problems which would probably be
explained by stack problems.
No, the problems are probably due to the FPC rtl not being initialised
for multi-threading. You will probably get slightly less problems if
you include the "cthreads" unit in your uses-clause and create a dummy
thread as soon as your program starts (after which you can destroy it
again), but even then you will get memory leaks and sporadic random
errors due to threadvars containing wrong values. As said above: it
does not work at this time (under unix-like platforms; in 2.3.1, it
should work on Windows).
The reason that it does not work on Unix-like platforms, is that there
is no way to make libthread inform FPC whenever a thread is created
(while this is possible on Windows), so the FPC rtl cannot initialise
the per-thread information properly. There is no known way to fix this
problem (although some people have guesses, no one really knows for
sure).
Jonas
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