Re: malloc()-free() and thread affinity
K?r?at wrote:
I recently developed a small test application to test multithreaded
behavior of malloc and free. The test application has two threads, one
allocates memory and the other deallocates that recently allocated memory.
I am a little surprised after this test : free() does not actually free
the memory which is allocated by another thread.
If I allocate/deallocate 5000 times my test applications memory usage
reaches ~320MB which proves above argument.
What do you think? Is it documented behavior of malloc and free? While
working on a highly mutithreaded environment how can I guarantee that
every allocations and deallocation to occur in the same thread?
It's impossible to tell whether the behaviour is expected because your
description is not detailed enough. In particular, you need to tell if the
threads run in parallel or whether one thread is run first and then the
other. Note that unless you programmatically make sure that they run
parallel you can not be sure whether they do so or not. Further, it you
should tell us how you actually measured the memory use.
FWIW, it is expected that allocated memory that is freed is not immediately
released to the operating system. However, it is reused by the application,
i.e. allocating memory again will also not request any memory from the OS.
The same principle is also not unheard of in the context of threads, i.e.
that each thread has its own private pool of memory.
Uli
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