Wave++ <wavexx@ngweb.it> wrote:
I’ve a little dumb question. Inside a multithreaded application all threads
must cooperate and all the memory inside the application is shared.
Are there some way to mprotect a segment of memory between threads so
ONLY some segments of memory are shared and/or detect when some threads
access these segments?
No, there is no way to protect memory between threads in the same
process.
You can use mutexes and stuff like that to avoid stomping on memory
while someone else is using it, but they are, essentially, advisory.
I probably already know the answer of this question. However I’m
setting up an application and I was deciding about splitting up the
application with multiple threads or multiple processes that shares
data. The multithreaded model fits better under my context and it’s
probably easier to set up.
Multi-threaded can be easier to setup – but the resiliency and ease
of debugging for the multi-process model is probably worth it.
This application doesn’t have a clare threaded model since each thread
could easily work indipendenty of each other sharing some structure for
communication. But I was thinking about the
implications of memory leaks and exceptions. A crash of a thread under
a multithreaded application would probably crash the whole application
but a crash of a separated program would probably stop the application
until the process come back. Of course I’ve my good reasons for thiking
that an application crash is worse than a little pause.
If you split things up into seperate processes, it is generally easier
to recover from a partial failure – and generally easier to track down
where the failure occurred and fix it.
So what I could “do” about managing threads over communicating and
syncronizing? There’s some way to protect, limit the thread execution
space?
There are all the posix synchronisation tools – mutexes, condvars,
reader/writer locks, etc. But, all are advisory – they allow you
to synchronise before accessing memory, but they provide no particular
protection.
In fact, even if you could protect memory between threads, the expected
behaviour on a failure would be a segmentation violation, which would
result in the failure of your large, do-everything process as well.
You can put mutexes, condvars, rwlocks, semaphores, etc in a shared
memory area between processes – so going multi-process does not lose
you the use of those tools. And, it gains you the segmented protection
that you are looking for – only the bits you explicitly want to share
will be shared, by putting them in a shared memory area.
-David
QNX Training Services
http://www.qnx.com/support/training/
Please followup in this newsgroup if you have further questions.
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