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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