errno was never set on error and thus the DIE_MSG_ERRNO did not properly
report what happened.

Found during changing Future member types.

Move io and lib related tests into io/ and lib/.

Our test dictionaries not must have a 'source' key with an array
created with files().
This ensures we use always correct paths regardless of the actual directory
we are currently in.

Until https://github.com/mesonbuild/meson/issues/8608 is not solved
we have to separately specify the tests name in a 'name' key.

Use getaddrinfo instead to get the socket information instead of
using always ipv4 sockets.
Pass host and port as strings for use with getaddrinfo.

Florian Fischer authored 4 years ago and Florian Schmaus committed 4 years ago

Modified-by: Florian Schmaus <flow@cs.fau.de>

Concurrently connecting and creating the server socket is racy.
Now the server socket is created before any Fiber is started
removing this race.
Note: The same race is theoretically in SimpleNetworkTest and
ConcurrenctEchoTest too but I haven't observed the failure yet

Empers IO design is based on a proactor pattern where each worker
can issue IO requests through its exclusive IoContext object which wraps an
io_uring instance.

IO completions are reaped at 4 places:
1. After a submit to collect inline completions
2. Before dispatching a new Fiber
3. When no new IO can be submitted because the completion queue is full
4. And by a global completer thread which gets notified about completions
   on worker IoContexts through registered eventfds

All IO requests are modeled as Future objects which can be either
instantiated and submitted manually, retrieved by POSIX-like non-blocking
or implicitly used by posix-like blocking functions.

User facing API is exported in the following headers:
* emper/io.hpp (POSIX-like)
* emper.h (POSIX-like)
* emper/io/Future.hpp

Catching short write/reads/sends and resubmitting the request without
unblocking the Fiber is supported.

Using AlarmFuture objects Fibers have a emper-native way to sleep for
a given time.

IO request timeouts with TimeoutWrapper class.
Request Cancellation is supported with Future::cancel() or the
CancelWrapper() Future class.

A proactor design demands that buffers are committed to the kernel
as long as the request is active. To guaranty memory safety Futures
get canceled in their Destructor which will only return after the committed
memory is free to use.

Linking Futures to chains is supported using the Future::SetDependency()
method. Future are submitted when their last Future gets submitted.
A linked Request will start if the previous has finished.
Error or partial completions will cancel the not started tail of a chain.

TODO: Handle possible situations where the CQ of the global completer is full
and no more sqe can be submitted to the SQ.