[Freeswitch-dev] Newbie question on switch_event_dup() and memory alloc/free in general

[Anthony Minessale]

yes any functions that take pointers to pointers and leave you with null
will indicate you don't have to do anything.


On Tue, Jun 29, 2010 at 2:23 PM, Mathieu Rene <mrene_lists at avgs.ca> wrote:

> Also note that switch_event_fire() will internally free the event once the
> handlers have processed it.
>
> Mathieu Rene
> Avant-Garde Solutions Inc
> Office: + 1 (514) 664-1044 x100
> Cell: +1 (514) 664-1044 x200
> mrene at avgs.ca
>
>
>
>
> On 2010-06-29, at 3:00 PM, Anthony Minessale wrote:
>
> This is mostly true
> minor corrections below:
>
> most functions who return an opaque pointer with no sign of a session or
> pool are expected to be destroyed.
> The rule of thumb is if they take an double pointer or return a pointer to
> something opaque or a string it's a safe assumption it needs to be destroyed
> either by looking for a corresponding destroy function or regular
> switch_safe_free on strings.
>
>
> On Tue, Jun 29, 2010 at 8:36 AM, Steven Ayre <steveayre at gmail.com> wrote:
>
>> memory free is sometimes used, but often not needed because of memory
>> pools.
>>
>> Sessions and channels have their own memory pool, anything creating memory
>> for one of them will not need freeing as when the session ends the entire
>> pool is destroyed. Similarly many modules have a pool which lasts for the
>> lifetime of the module.
>>
>> There are other functions which will need freeing though... I suggest that
>> you use switch_safe_free() to be consistent with the rest of freeswitch.
>> It's just a wrapper on free which doesn't call it for a null pointer
>> (avoiding a segfault on some systems).
>>
>> Some examples:
>> - switch_snprintf & switch_mprintf needs a free (is given no pool or
>> object with a pool)
>>
>      *switch_snprintf does not need free it takes a buffer and memory size
> as args like real snprintf*
>
>
>> - switch_core_session_sprintf does not need a free (it's given a session,
>> memory is allocated from its pool)
>> - switch_channel_expand_variables sometimes needs free, sometimes doesn't
>> (you give it a buffer, if it's large enough its used and returned otherwise
>> it creates a new one, so you should check the return value against the
>> buffer to avoid either freeing a const char or a buffer twice).
>>
>> *switch_channel_expand_variables only uses dynamic memory if something
> was expanded in the string.  If it does not expand anything it returns the
> original input pointer so you can tell if you need to free it if the output
> != input string.*
>
>
>
>
>
>> -Steve
>>
>>
>> On 29 June 2010 06:19, Paul Li <plite2012 at gmail.com> wrote:
>>
>>> A lot of FreeSwitch core APIs, such as switch_event_dup(switch_event_t
>>> **event, switch_event_t *todup), returns a pointer to an allocated
>>> memory chunk, should the caller always releases that memory chunk by
>>> calling a proper API, such as switch_event_destroy(switch_event_t
>>> **event)?
>>>
>>> I could not find any documentation to detail the general rule
>>> regarding memory allocation/free when using the core APIs.
>>>
>>> Thank you for your attention!
>>>
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>>
>>
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>>
>
>
> --
> Anthony Minessale II
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-- 
Anthony Minessale II

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