multi transfer book keeping using mid #16761
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Change multi's book keeping of transfers to no longer use lists,
but a special table and bitsets for unsigned int values.
`multi-xfers` is the `uint_tbl` where `multi_add_handle()` inserts
a new transfer which assigns it a unique identifier `mid`. Use
bitsets to keep track of transfers that are in state "process"
or "pending" or "msgsent".
Use sparse bitsets to replace `conn->easyq` and event handlings
tracking of transfers per socket. Instead of pointers, keep the
mids involved.
Provide base data structures and document them in docs/internal:
* `uint_tbl`: a table of transfers with `mid` as lookup key,
handing out a mid for adds between 0 - capacity.
* `uint_bset`: a bitset keeping unsigned ints from 0 - capacity.
* `uint_spbset`: a sparse bitset for keeping a small number of
unsigned int values
* `uint_hash`: for associating `mid`s with a pointer.
This makes the `mid` the recommended way to refer to transfers
inside the same multi without risk of running into a UAF.
Modifying table and bitsets is safe while iterating over them.
Overall memory requirements are lower as with the double linked
list apprach.
Use UINT_MAX everywhere as invalid mid number, replacing extra define Add more tracing of multi_add/remove/cleanup with mid and counters
bagder
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Apr 17, 2025
nbaws
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this pull request
Apr 26, 2025
Change multi's book keeping of transfers to no longer use lists, but a special table and bitsets for unsigned int values. `multi-xfers` is the `uint_tbl` where `multi_add_handle()` inserts a new transfer which assigns it a unique identifier `mid`. Use bitsets to keep track of transfers that are in state "process" or "pending" or "msgsent". Use sparse bitsets to replace `conn->easyq` and event handlings tracking of transfers per socket. Instead of pointers, keep the mids involved. Provide base data structures and document them in docs/internal: * `uint_tbl`: a table of transfers with `mid` as lookup key, handing out a mid for adds between 0 - capacity. * `uint_bset`: a bitset keeping unsigned ints from 0 - capacity. * `uint_spbset`: a sparse bitset for keeping a small number of unsigned int values * `uint_hash`: for associating `mid`s with a pointer. This makes the `mid` the recommended way to refer to transfers inside the same multi without risk of running into a UAF. Modifying table and bitsets is safe while iterating over them. Overall memory requirements are lower as with the double linked list apprach. Closes curl#16761
nbaws
pushed a commit
to nbaws/curl
that referenced
this pull request
Apr 26, 2025
Change multi's book keeping of transfers to no longer use lists, but a special table and bitsets for unsigned int values. `multi-xfers` is the `uint_tbl` where `multi_add_handle()` inserts a new transfer which assigns it a unique identifier `mid`. Use bitsets to keep track of transfers that are in state "process" or "pending" or "msgsent". Use sparse bitsets to replace `conn->easyq` and event handlings tracking of transfers per socket. Instead of pointers, keep the mids involved. Provide base data structures and document them in docs/internal: * `uint_tbl`: a table of transfers with `mid` as lookup key, handing out a mid for adds between 0 - capacity. * `uint_bset`: a bitset keeping unsigned ints from 0 - capacity. * `uint_spbset`: a sparse bitset for keeping a small number of unsigned int values * `uint_hash`: for associating `mid`s with a pointer. This makes the `mid` the recommended way to refer to transfers inside the same multi without risk of running into a UAF. Modifying table and bitsets is safe while iterating over them. Overall memory requirements are lower as with the double linked list apprach. Closes curl#16761
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Change multi's book keeping of transfers to no longer use lists, but a special table and bitsets for unsigned int values.
multi->xfersis theuint_tblwheremulti_add_handle()inserts a new transfer which assigns it a unique identifiermid. Use bitsets to keep track of transfers that are in state "process" or "pending" or "msgsent".Use sparse bitsets to replace
conn->easyqand event handlings tracking of transfers per socket.Provide base data structures and document them in docs/internal:
uint_tbl: a table of transfers withmidas lookup key, handing out a mid for adds between 0 - capacity.uint_bset: a bitset keeping unsigned ints from 0 - capacity.uint_spbset: a sparse bitset for keeping a small number of unsigned int valuesuint_hash: for associatingmids with a pointer.This makes the
midthe recommended way to refer to transfers inside the same multi without risk of running into a UAF.Modifying table and bitsets is safe while iterating over them. Overall memory requirements are lower than with the double linked list apprach.
memory
To keep track of 1000 transfers, the dominating factor before were 2
struct Curl_llist_nodein eachCurl_easy. Each occupies 32 bytes each, so 64 KB for 1000 easy handles.With this PR, we have one table and 3 bitsets, which are kept 25% free. The table uses 8 bytes per possible entry, so ~10 KB for 1300 rows of capacity. A bitset for numbers 0-1299 occupies 168 bytes, which makes ~540 bytes for all three. Plus a "sparse" bitset per connection. For the case that each transfer has its own connection, that adds 32 bytes for each one.
*) the usual rounding errors with 1000 ~= 1024 apply.😌