[UnblockOnMainActorTest] adjust workload to log level

See merge request !303

The UnblockOnMainActorTest regularly timeout in our CI
which looks to be a regular timeout because I could easily reproduce
the timeout on fauibig03.

Hopefully this change fixes regular timeouts like
https://gitlab.cs.fau.de/aj46ezos/emper/-/jobs/506757
in the CI and only leaves real faulty timeouts.

[meson] add boost as dependency

See merge request !301

I setup a new development environment and emper did not compile because
emper::io::Stats use the circular_buffer provided by boost.
Boost was not installed and our build-system failed to detect it.

This change adds the header-only boost dependency to emper.
https://mesonbuild.com/Dependencies.html#boost
The header-only dependency is enough to build emper default configuration.

When linking against boost is required we use the 'modules' karg.

[Dispatcher] replace deprecated pthread_yield with sched_yield

See merge request !302

Compilation with gcc on ubuntu 21.10 fails because pthread_yield is
apparently deprecated and should be replaced with sched_yield.

gcc --version
gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0

properly cancel future callbacks

See merge request !297

* Document data races of a future's state.
* Get and set a Future's state only through methods. This helps to
  add possibly needed atomic operations.
* Use atomics to get/set cancel and prepare state in IO_SINGLE_URING vaiant
* Add more IO debug messages
* Use the BPS of Futures with callbacks similar to those of forgotten
  ones to signal their preparation. The preparation mark the
  last moment where the Future is used in EMPER and after that the memory
  can be dropped.
  ATTENTION: This means not that the used resources of the IO request
  can be dropped. The kernel may still use a supplied buffer for example.
* Fix Future chain cancellation in SubmitActor

Currently canceling Futures would never happen because we
issued the cancel request only with the pointer of the future.
This works more by coincidence than by design because
the PointerTags::Future tagged onto the submitted future pointer is 0.

This does not work for callbacks because they are tagged with a
PointerTags != 0 and they don't use their callback pointer rather
than the future pointer.

Fix this by exporting the tagging from IoContext::prepareFutureChain
into IoContext::createFutureTag and use this when submitting a cancel
sqe.

Warn the user that they have to manually take care of the memory safety
of the callback because we can not await the callback in Future::cancel.

Add a test case to CancelFutureTest.

[Common] introduce a CACHE_LINE_SIZE define

See merge request !299

[SpuriousFutexSemaphore] futex are 32 bits on all platforms

See merge request !300

This define will be used in future patches.

Make Scheduler within Runtime public API

See merge request !298

The Runtime class was never a good place for inRuntime(): due its
central role in EMPER's architecture, it causes easily include
cycles. Furthermore, the API was not ideal, once we would move Runtime
into emper::, it would become emper::Runtime::inRuntime().

We declare emper::Emper::inRuntime and emper::Emper::assertInRuntime()
as static struct functions to avoid multiple definitions, and then use
a constexpr function "alias" to have those functions available in the
emper:: namespace.

[IO] overhaul SQPOLL support

See merge request !210

[CI] print the number of available CPUs

See merge request !290

[qsort] fix implicit widening clang-tidy error

See merge request !292

[ConcurrentNetworkEchoTest] add optional computation per echo

See merge request !293

This makes the test closer to our echoserver.

Two meson options control the io_uring sqpoll feature:
* io_uring_sqpoll - enable sq polling
* io_uring_shared_poller - share the polling thread between all io_urings

Since 5.12 the IORING_SETUP_ATTACH_WQ only causes sharing of
poller threads not the work queues.
See: https://github.com/axboe/liburing/issues/349

When using SQPOLL the userspace has no good way to
know how many sqes the kernel has consumed therefore we
wait for available sqes using io_uring_sqring_wait if there
was no usable sqe.

Remove the GlobalIoContext::registerLock and register all worker
io_uring eventfd reads at the beginning of the completer function.
Also register all the worker io_uring eventfds since they never change
and it hopefully reduces overhead in the global io_uring.

fix {RwLocked,SharedMutex}UnboundedQueues

See merge request !291

A "fast check" consists of our smoke tests and the fast static analysis
this ensures that the emper variants even build successfully and
are not totally broken.

Previous RwLockUnboundedQueue versions did not drop their rw lock
before trying to grab the wr lock which may result in a deadlock.
Also wrap the noisy POSIX functions names in cleaner helper functions.

Introduce waitfree work/io-stealing

See merge request !289

Waitfree IO-stealing can be enabled with the meson option
-Dio_waitfree_stealing.

Waitfree work stealing is configured with the meson option
'waitfree_work_stealing'.

The retry logic is intentionally left in the Queues and not lifted to
the scheduler to reuse the load of an unsuccessful CAS.

Consider the following pseudo code examples:

steal() -> bool:                       steal() -> res
  load                                   load
loop:                                    if empty return EMPTY
  if empty return EMPTY                  cas
  cas                                    return cas ? STOLEN : LOST_RACE
  if not WAITFREE and not cas:
    goto loop                          outer():
  return cas ? STOLEN : LOST_RACE      loop:
                                         res = steal()
outer():                                 if not WAITFREE and res == LOST_RACE:
  steal()                                  goto loop

In the right example the value loaded by a possible unsuccessful CAS
can not be reused. And a loop of unsuccessful CAS' will result in
double loads.

The retries are configurable through a template variable maxRetries.
* maxRetries < 0: indefinitely retries
* maxRetries >= 0: maxRetries

Multiple changes to improve IO stealing

See merge request !288

This has the benefit of adequat sized intermediate arrays reducing
the needed stack size.

[gitlab-ci] Cache subprojects/packagecache

See merge request !287