Am 22.03.2012 15:32, schrieb Antonio Fortuny:
Hi folks.
Wen launching a thread, the process responsible for the thread object
creation and the call to TThread.Start and the thread EXECUTE procedure,
run in parallel. That's why the SYNCHRONIZE procedure exists and that
the developer has to pay attention to not share code between threads.
So far, so good.
Now imagine that the EXECUTE procedure of a thread creates a useful
object (TMyObject) with properties and methods. This thread is launched
half a dozen times to process half a dozen simultaneous operations.
My question is:
How the properties and methods of the TMyObject created in every
launched thread are they managed from one thread to another. As far as
the data segment is concerned, no problem, I guess that every instance
of the TMyObject has its own data in its thread address space: no mix.
But what about the code and the local methods stack: will it be shared ?
And if answer is yes, to what should I take care ?
The question is far from trivial: I try to keep the EXECUTE procedure as
small as possible and spread the code and data over a number of
specialized units avoiding to load the EXECUTE procedure stack with
heavy data ans structures.
I apologize if my question doesn't sound very clear, but it's not even
clear in my mind :-[
I don't know whether I understood your question correctly, but I'll try
to answer:
* Each thread has it's own stack space, so objects/data located on the
stack is (normally) not shared between threads (an exception for example
are writeable local consts, because they act like static variables)
* The part of the executable which runs between "begin ... end." in the
main project file is a thread itself (also called "main thread"), so one
does not need to differentiate between threads started by you and the
thread started by the operating system at process start
* The Heap (the area of the memory where e.g. object instances and data
allocated with New/GetMem resides) is shared between all threads. So you
need to be careful if you create an object in thread A and change it in
thread B (and thread A as well). But if you create an object in method X
that is called by thread A and thread B and you never pass the instance
to another thread you have no problem, because no other thread then
knows the reference to this object.
I hope this clarifies things a bit. Feel free to ask back if you need to.
Regards,
Sven
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