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From: Vikash Badal <Vikash.Badal@is.co.za>
To: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org>
Date: Fri, 11 Jun 2010 21:23:43 +0200
Thread-Topic: threads and malloc/free  on freebsd 8.0
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Subject: threads and malloc/free  on freebsd 8.0
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Greetings.

I have a thread socket application that seems to be behaving strangely

In a worker thread, I have the following.

<CODE>-----------
=20  LogMessage(DEBUG_0, "allocated %ld", malloc_usable_size(inst));
=20 =20
=20  free(inst);
=20 =20
=20  LogMessage(DEBUG_0, "after free allocated %ld", malloc_usable_size(i=
nst));

=20  free(inst);
=20 =20
=20   return 0;
-----------</CODE>

output> allocated 2304
output> after free allocated 2304

from playing around, this should have segfaulted but it didn't:


if I try this from a non threaded, non socket code:
<CODE>------------------
=20  char *z;

=20  z =3D (char*)malloc(1000);
=20  printf("malloc is %ld\n", malloc_usable_size(z));
=20  free(z);
=20  printf("after malloc is %ld\n", malloc_usable_size(z));
------------------</CODE>

Output> malloc is 1024
Output> Segmentation fault (core dumped)



Can anyone enlighten me ? why did the 2nd free not cause a segmentation f=
ault ?


If im not clear, please forgive me.


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