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Re: realloc() and POSIX threads

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On 9/27/2019 2:29 PM, Doug Weiman wrote:
> 	My question may not belong in this group - my apologies if that
> is the case.
> 
> 	I have some application that allocates memory with malloc(), and
> then uses the resulting pointer as an argument to a POSIX thread that is
> launched immediately after. While the thread is doing its thing with the
> memory pointed to by this pointer, the application augments that pointer
> with realloc().
> 
> 	My understanding is that realloc() is no guaranteed to keep the
> original pointer. That is, if necessary, realloc() will obtain a
> different pointer to a memory region with enough space, and copy here the
> contents of the memory region pointed to by the original pointer, finally
> returning thee new pointer to the caller.
> 
> 	This is, of course, potentially disastrous to the thread above,
> which is still operating on a memory area now deallocated. I mean, you
> may be lucky and the area will still be usable, but sooner or later the
> whole thing will blow up in yor face.
> 
> 	Is there a way to implement the scenario above (memory
> allocation, thread creation, memory reallocation) safely, so that the
> thread can be guaranteed to still have access to valid memory? One could
> use thread mutexes, but that would effectively serialize things.
> 
> 	Any other suggestions? Or is this the kind of thing that one just
> ought not to do, period? For a number of reasons, getting the thread
> itself to allocate the memory is not an option.
> 

Never call realloc on live memory, where other threads can be using it. 
Instead, wait for the memory to go into a quiescent state, then you can 
free it, and call realloc.

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realloc() and POSIX threads Doug Weiman <no@nyet.net> - 2019-09-27 21:29 +0000
  Re: realloc() and POSIX threads Robert Wessel <robertwessel2@yahoo.com> - 2019-09-27 17:11 -0500
  Re: realloc() and POSIX threads Florian Weimer <fw@deneb.enyo.de> - 2019-09-28 09:27 +0200
  Re: realloc() and POSIX threads Melzzzzz <Melzzzzz@zzzzz.com> - 2019-09-28 08:42 +0000
  Re: realloc() and POSIX threads "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-09-28 03:53 -0700
    Re: realloc() and POSIX threads "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-09-28 03:55 -0700
  Re: realloc() and POSIX threads Richard Damon <Richard@Damon-Family.org> - 2019-09-28 08:29 -0400
    Re: realloc() and POSIX threads Doug Weiman <no@nyet.net> - 2019-09-28 15:06 +0000
    Re: realloc() and POSIX threads "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-09-28 15:19 -0700
      Re: realloc() and POSIX threads "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-09-28 15:23 -0700

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