[uClibc] Re: Is malloc thread safe?

[Miles Bader]

malloc does having locking code to deal with threads; however it has not
really been tested (though it's simple enough code).

> I tried to turn on: setenv MALLOC_DEBUG=X; to view the debug messages
> from the uclibc-malloc debugging code, but the information from doing
> so was too disjointed for me to follow; as it seemed that one thread
> would malloc and start to print debug msgs and then in the middle of
> those print statements the kernel would change the time-slice to let
> another thread/process have cpu time which would attempt to alloc new
> memory....

Um, well, malloc's not part of the kernel, so of course that can
happen -- the kernel has no idea that it shouldn't switch threads.

However, it also shouldn't cause problems: the interrupted malloc should
be holding a mutex (specifically the one called `lock' in the heap data
structure; or if on a system using sbrk, __malloc_sbrk_lock).  The
interrupting thread should attempt to get this mutex, resulting in it
waiting until the first thread is done with it.

-Miles
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