Re: dumb apr_pool question

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Thanks guys. Interesting info. It really helped.

On 01/12/2018 12:12 AM, Yann Ylavic wrote:
> On Thu, Jan 11, 2018 at 3:05 PM, Eric Covener <covener@xxxxxxxxx> wrote:
>> On Thu, Jan 11, 2018 at 3:55 AM, Simon Walter <simon@xxxxxxxxxx> wrote:
>>>
>>> I suppose that the pool is keeping track of all it's allocations and if
>>> something is still referenced, it will not free it.
>>
>> No the only tracking is done by whoever manages the lifecycle of the
>> pool itself -- no magic.
>>
>> apr_pool_destroy will call free() or munmap or any underlying
>> allocation on the way out, returning it to the OS.
> 
> Actually the memory is returned to the (apr_)allocator, which itself
> may cache for further reuse.
> One can use apr_allocator_max_free_set() to limit the number of pages
> cached (no limit by default), e.g. something like the following code
> based on Simon's (not even compile tested...):
> 
> int main(int ArgCount, char * Arg[])
> {
>     char * String;
>     apr_pool_t * Pool = NULL;
>     apr_allocator_t * Alloc = NULL;
>     apr_initialize();
> 
>     /* New allocator (not the default/unlimited one) */
>     apr_allocator_create(&Alloc);
>     /* Cache one page only (may be 4K pages, not system's),
>      * zero is unlimited, so the cache is always 1 page min... */
>     apr_allocator_max_free_set(Alloc, 1/*page*/);
>     /* Use this allocator for the pool */
>     apr_pool_create_ex(&Pool, NULL, NULL, Alloc);
>     /* Destroy Alloc when destroying Pool */
>     apr_allocator_owner_set(Alloc, Pool);
> 
> 
>     /* Won't crash (possibly), don't do that for real... */
>     String = apr_pstrdup(Pool, "small alloc");
>     apr_pool_clear(Pool);
>     printf("String: %s\n", String);
> 
>     /* Should crash */
>     (void)apr_palloc(Pool, 4100);
>     (void)apr_palloc(Pool, 4100);
>     (void)apr_palloc(Pool, 4100);
>     String = apr_pstrdup(Pool, "small alloc");
>     apr_pool_clear(Pool);
>     printf("String: %s\n", String);
> 
>     /* Should also crash */
>     String = apr_pstrdup(Pool, "small alloc");
>     apr_pool_destroy(Pool); /* + Alloc */
>     printf("String: %s\n", String);
> 
>     apr_terminate();
>     return 0;
> }
> 
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