From the developer documentation [0]:
"Standard programming error: memorize a pointer to the ith element of a
vector, and then expand the vector. Vectors expand by 3/2, so such code
may appear to work for a period of time. Correct code almost always
memorizes vector indices which are invariant across reallocations."
"Pools
Vppinfra pools combine vectors and bitmaps to rapidly allocate and free
fixed-size data structures with independent lifetimes. Pools are perfect
for allocating per-session structures."
Hope this helps,
-daw-
[0]
https://fdio-vpp.readthedocs.io/en/latest/gettingstarted/developers/infrastructure.html
On 5/6/2020 2:22 PM, Satya Murthy wrote:
Hi,
We are seeing some issue in our plugin that seems to caused by the
change of pointer for a pool element.
The scenario is as below. Can you please let us know , if this can
really occur.
1. We have multiple workers
2. We have one global pool of custom-structures ( this is a non-fixed
pool)
3. This global pool is protected by a lock for addition and deletion.
4. However, it is not protected for reading. So, all workers refer
read entries from this pool by using pool_elt_at_index()
5. All the workers keep on adding and deleting elements in this pool
by taking lock.
6. What we are seeing is, the pointer returned by
pool_elt_at_index(global_pool, index)
is getting changed in between and causing some issue in our logic.
Couple of questions we have is :
1 ) If a pool element is getting used (not-free-element), Until that
element is put back again into the pool, can we assume that the
address of the element remain same and will not get chagned by pool
resizing.
2) Having pools that spans across threads will cause any issues like
this while reading the elements ( though we protect the pool for
add/del of elements using a spin lock) ?
--
Thanks & Regards,
Murthy
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