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

[Anthony Minessale]

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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