Add a bitset `dirty` to the multi handle. The presence of a transfer int
he "dirty" set means: this transfer has something to do ASAP.
"dirty" is set by multiplexing protocols like HTTP/2 and 3 when
encountering response data for another transfer than the current one.
"dirty" is set by protocols that want to be called.
Implementation:
* just an additional `uint_bset` in the multi handle
* `Curl_multi_mark_dirty()` to add a transfer to the dirty set.
* `multi_runsingle()` clears the dirty bit of the transfer at
start. Without new dirty marks, this empties the set after
al dirty transfers have been run.
* `multi_timeout()` immediately gives the current time and
timeout_ms == 0 when dirty transfers are present.
* multi_event: marks all transfers tracked for a socket as dirty.
Then marks all expired transfers as dirty. Then it runs
all dirty transfers.
With this mechanism:
* Most uses of `EXPIRE_RUN_NOW` are replaced by `Curl_multi_mark_dirty()`
* `Curl_multi_mark_dirty()` is cheaper than querying if a transfer is
already dirty or set for timeout. There is no need to check, just do it.
* `data->state.select_bits` is eliminated. We need no longer to
simulate a poll event to make a transfer run.
Closes#17662
With a meta_hash at each connection (similar to easy handle, let
multi_ev.c store its pollsets as meta data, no longer needing its own
hashes.
This eliminates the last use of Curl_hash_offt. Remove it.
Closes#17095
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#16761
Add a standalong hash table for curl_offt_t as key. This allows a
smaller memory footprint and faster lookups as we do not need to deal
with variable key lengths.
Use in all places we had the standard hash for this purpose.
Closes#16442
Rework the event based handling of transfers and connections to
be "localized" into a single source file with clearer dependencies.
- add multi_ev.c and multi_ev.h
- add docs/internal/MULTI-EV.md to explain the overall workings
- only do event handling book keeping when the socket callback
is set
- add handling for "connection only" event tracking, when internal
easy handles are used that are not really tied to a connection.
Used in connection pool.
- remove transfer member "last_poll" and connections "shutdown_poll"
and keep all that internal to multi_ev.c
- add CURL_TRC_M() for tracing of "multi" related things, including
event handling and connection pool operations. Add new trace
feature "multi" for trace config.
multi traces will show exactly what is going on in regard to
event handling.
- multi: trace transfers "mstate" in every CURL_TRC_M() call
- make internal trace buffer 2048 bytes and end the silliness
with +n here -m there. Adjust test 1652 expectations of resulting
length and input edge cases.
- add trace feature "lib-ids" to perfix libcurl traces with transfer
and connection ids. Useful for debugging libcurl applications.
Closes#16308
