Deallocating memory in isc code.

[Mark Andrews]

In message <BANLkTi=DW4SsSphHF5MJ3QV4ofSquTKkGA at mail.gmail.com>, kalpesh varyani writes:
> Hi,
> 
> Is it necessary to deallocate memory assigned using isc_mem_get() by
> explicitly using isc_mem_free()?

No.  You use isc_mem_put().  See <isc/mem.h>
 
> Ref: File builtin.c is available at
> ftp://1node.net/linux/bind-9.7.0b1/bin/named/*builtin*.*c*<ftp://1node.net/linux/bind-9.7.0b1/bin/named/builtin.c>
> 
> Following is the code snippet:
> 
> static isc_result_t builtin_create(const char *zone, int argc, char
> **argv,void *driverdata, void **dbdata)
> {
> ...
> builtin_t *empty; <-- Local variable.
> ...
> empty = *isc_mem_get*(ns_g_mctx, sizeof(*empty)); <-- Memory assigned using
> isc_mem_get
> server = isc_mem_strdup(ns_g_mctx, argv[1]);
> contact = isc_mem_strdup(ns_g_mctx, argv[2]);

If any of the allocations failed then free all that succeeded.
Return the address of empty_builtin in that case.

> if (empty == NULL || server == NULL || contact == NULL) {
>     *dbdata = &empty_builtin;
>     if (server != NULL)
>         isc_mem_free(ns_g_mctx, server);
>     if (contact != NULL)
>         isc_mem_free(ns_g_mctx, contact);
>     if (empty != NULL)
>         isc_mem_put(ns_g_mctx, empty, sizeof (*empty));
> }
> ...
> }
> 
> Here memory is assigned using isc_mem_get() however isc_mem_free() is
> conditional. Thus if conditions are false then there will be no
> isc_mem_free().
> 
> 1. Even if *builtin_t *empty; *is local to the function *builtin_create*, can
> it cause memory leak?

> 2. what should be the rerurn value of *isc_mem_strdup()* on success/failure?
> 
> Regards,
> Kalpesh
> 
> --20cf303f6bc668d58504a5332e6c
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> 
> <div>Hi,</div>
> <div>=A0</div>
> <div>Is it necessary to deallocate memory assigned using isc_mem_get() by e=
> xplicitly using isc_mem_free()?</div>
> <div>=A0</div>
> <div>Ref: File=A0builtin.c is available at <a href=3D"ftp://1node.net/linux=
> /bind-9.7.0b1/bin/named/builtin.c"><font color=3D"#0e774a">ftp://1node.net/=
> linux/bind-9.7.0b1/bin/named/<b>builtin</b>.<b>c</b></font></a></div>
> <div>=A0</div>
> <div>Following is the code snippet:</div>
> <div><span lang=3D"EN"></span>=A0</div>
> <div><span lang=3D"EN">static isc_result_t builtin_create(const char *zone,=
>  int argc, char **argv,void *driverdata, void **dbdata) </span></div>
> <div><span lang=3D"EN">{</span></div>
> <div><span lang=3D"EN">...<br></span><span lang=3D"EN"><span lang=3D"EN">bu=
> iltin_t *empty; <-- Local variable.</span></span></div>
> <div><span lang=3D"EN"><span lang=3D"EN">...</span><br></span><span lang=3D=
> "EN"><span lang=3D"EN">empty =3D <strong>isc_mem_get</strong>(ns_g_mctx, si=
> zeof(*empty)); <-- Memory assigned using isc_mem_get<br>server =3D isc_m=
> em_strdup(ns_g_mctx, argv[1]);<br>
> contact =3D isc_mem_strdup(ns_g_mctx, argv[2]);<br>if (empty =3D=3D NULL ||=
>  server =3D=3D NULL || contact =3D=3D NULL) {<br>=A0=A0=A0 *dbdata =3D &amp=
> ;empty_builtin;<br>=A0=A0=A0 if (server !=3D NULL)=A0=A0=A0=A0<br>=A0=A0=A0=
> =A0=A0=A0=A0 isc_mem_free(ns_g_mctx, server);<br>
> =A0=A0=A0 if (contact !=3D NULL)<br>=A0=A0=A0=A0=A0=A0=A0 isc_mem_free(ns_g=
> _mctx, contact);<br>=A0=A0=A0 if (empty !=3D NULL)<br>=A0=A0=A0=A0=A0=A0=A0=
>  isc_mem_put(ns_g_mctx, empty, sizeof (*empty));<br>} </span></span><span l=
> ang=3D"EN"><span lang=3D"EN"></span></span></div>
> 
> <div><span lang=3D"EN">...</span></div>
> <div><span lang=3D"EN">}</span></div>
> <div><span lang=3D"EN"></span>=A0</div>
> <div><span lang=3D"EN">Here memory is assigned using isc_mem_get() however =
> isc_mem_free() is conditional. Thus if conditions are false then there will=
>  be no isc_mem_free().</span></div>
> <div><span lang=3D"EN"></span>=A0</div>
> <div><span lang=3D"EN">1. Even if <span lang=3D"EN"><strong>builtin_t *empt=
> y; </strong>is local to the function <strong>builtin_create</strong>,=A0can=
>  it cause memory leak?</span></span></div>
> <div><span lang=3D"EN"><span lang=3D"EN">2. what should be the rerurn value=
>  of <strong>isc_mem_strdup()</strong> on success/failure?</span></span></di=
> v>
> <div><span lang=3D"EN"><span lang=3D"EN"></span></span>=A0</div>
> <div><span lang=3D"EN"><span lang=3D"EN">Regards,</span></span></div>
> <div><span lang=3D"EN"><span lang=3D"EN">Kalpesh</span></span></div>
> 
> --20cf303f6bc668d58504a5332e6c--
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org