Let us always base srw_lock on our own std::atomic<uint32_t>
based rw_lock. In this way, we can extend the locks in a portable
way across all platforms.

We will use futex system calls where available:
Linux, OpenBSD, and Microsoft Windows.

Elsewhere, we will emulate futex with a mutex and a condition variable.

Thanks to Daniel Black for testing this on OpenBSD.

os_thread_pf(): Remove.

os_thread_eq(), os_thread_yield(), os_thread_get_curr_id():
Define as macros.

ut_print_timestamp(), ut_sprintf_timestamp(): Simplify.

When executing set operations in a pipeline using only one temporary table
additional scans of intermediate results may be needed. The scans are
performed with usage of the rnd_next() handler function that might
leave record buffers used for the temporary table not in a state that
is good for following writes into the table. For example it happens for
aria engine when the last call of rnd_next() encounters only deleted
records. Thus a cleanup of record buffers is needed after each such scan
of the temporary table.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

This change is needed in 10.5 to avoid extra malloc calls in val_str().
In 10.6 it's not needed anymore but the extra +1 byte doesn't harm
that much.

- Fold long comment rows and updated comments
- Moved one private function in class Item_func_rand among other private
  functions

This is for Oracle compatiblity. ENABLED is in Oracle the default case
and just ensures that the NOT NULL constraints will be tested, which is
also default in MariaDB

A side effect of MDEV-16264 is that a large number of threads will
be created at server startup, to be destroyed after a minute or two.

One source of such thread creation is srv_start_periodic_timer().
InnoDB is creating 3 periodic tasks: srv_master_callback (1Hz)
srv_error_monitor_task (1Hz), and srv_monitor_task (0.2Hz).

It appears that we can merge srv_error_monitor_task and srv_monitor_task
and have them invoked 4 times per minute (every 15 seconds). This will
affect our ability to enforce innodb_fatal_semaphore_wait_threshold and
some computations around BUF_LRU_STAT_N_INTERVAL.

We could remove srv_master_callback along with the DROP TABLE queue
at some point of time in the future. We must keep it independent
of the innodb_fatal_semaphore_wait_threshold detection, because
the background DROP TABLE queue could get stuck due to dict_sys
being locked by another thread. For now, srv_master_callback
must be invoked once per second, so that
innodb_flush_log_at_timeout=1 can work.

BUF_LRU_STAT_N_INTERVAL: Reduce the precision and extend the time
from 50*1 second to 4*15 seconds.

srv_error_monitor_timer: Remove.

MAX_MUTEX_NOWAIT: Increase from 20*1 second to 2*15 seconds.

srv_refresh_innodb_monitor_stats(): Avoid a repeated call to time(NULL).
Change the interval to less than 60 seconds.

srv_monitor(): Renamed from srv_monitor_task.

srv_monitor_task(): Renamed from srv_error_monitor_task().
Invoked only once in 15 seconds. Invoke also srv_monitor().
Increase the fatal_cnt threshold from 10*1 second to 1*15 seconds.

sync_array_print_long_waits_low(): Invoke time(NULL) only once.
Remove a bogus message about printouts for 30 seconds. Those
printouts were effectively already disabled in MDEV-16264
(commit 5e62b6a5).

The purpose of the InnoDB page cleaner subsystem is to write out
modified pages from the buffer pool to data files. When the
innodb_max_dirty_pages_pct_lwm is not exceeded or
innodb_adaptive_flushing=ON decides not to write out anything,
the page cleaner should keep sleeping indefinitely until the state
of the system changes: a dirty page is added to the buffer pool such
that the page cleaner would no longer be idle.

buf_flush_page_cleaner(): Explicitly note when the page cleaner is idle.
When that happens, use mysql_cond_wait() instead of mysql_cond_timedwait().

buf_flush_insert_into_flush_list(): Wake up the page cleaner if needed.

innodb_max_dirty_pages_pct_update(),
innodb_max_dirty_pages_pct_lwm_update():
Wake up the page cleaner just in case.

Note: buf_flush_ahead(), buf_flush_wait_flushed() and shutdown are
already waking up the page cleaner thread.

Kudos to Marko for finding.

This partially reverts commit 6479006e.

Remove the constant tpool::aio::N_PENDING, which has no
intrinsic meaning for the tpool.

tpool::aio::N_PENDING: Replaces OS_AIO_N_PENDING_IOS_PER_THREAD.
This limits two similar things: the number of outstanding requests
that a thread may io_submit(), and the number of completed requests
collected at a time by io_getevents().

In the asynchronous I/O interface, InnoDB is invoking io_getevents()
with a timeout value of half a second, and requesting exactly 1 event
at a time.

The reason to have such a short timeout is to facilitate shutdown.

We can do better: Use an infinite timeout, wait for a larger maximum
number of events. On shutdown, we will invoke io_destroy(), which
should lead to the io_getevents system call reporting EINVAL.

my_getevents(): Reimplement the libaio io_getevents() by only invoking
the system call. The library implementation would try to elide the
system call and return 0 immediately if aio_ring_is_empty() holds.
Here, we do want a blocking system call, not 100% CPU usage. Neither
do we want the aio_ring_is_empty() trigger SIGSEGV because it is
dereferencing some memory that was freed by io_destroy().

For reading trx_t::state we can avoid acquiring trx_t::mutex.
Atomic load and store should be similar to normal load and store
on most instruction set architectures. The atomicity of the operation
would merely prohibit the compiler from reordering some operations.

We must avoid acquiring a latch while we are already holding one.
The tablespace latch was being acquired recursively in some
operations that allocate or free pages.

fts_cache_t::init_lock: Replace with mutex. This was only acquired
in exclusive mode.

fts_cache_t::lock: Replace with mutex. The only read-lock user was
i_s_fts_index_cache_fill() for producing content for the view
INFORMATION_SCHEMA.INNODB_FT_INDEX_CACHE.

Many InnoDB rw-locks unnecessarily depend on the complex
InnoDB rw_lock_t implementation that support the SX lock mode
as well as recursive acquisition of X or SX locks.
One of them is the bunch of adaptive hash index search latches,
instrumented as btr_search_latch in PERFORMANCE_SCHEMA.
Let us introduce a simpler lock for those in order to
reduce overhead.

srw_lock: A simple read-write lock that does not support recursion.
On Microsoft Windows, this wraps SRWLOCK, only adding
runtime overhead if PERFORMANCE_SCHEMA is enabled.
On Linux (all architectures), this is implemented with
std::atomic<uint32_t> and the futex system call.
On other platforms, we will wrap mysql_rwlock_t with
zero runtime overhead.

The PERFORMANCE_SCHEMA instrumentation differs
from InnoDB rw_lock_t in that we will only invoke
PSI_RWLOCK_CALL(start_rwlock_wrwait) or
PSI_RWLOCK_CALL(start_rwlock_rdwait)
if there is an actual conflict.

The greedy fetch_add(1) approach of read_trylock() may cause
starvation of a waiting write lock request. Let us use a
compare-and-swap for the read lock acquisition in order to
guarantee the progress of writers.

Do not resend metadata, if metadata does not change between prepare and
execute of prepared statement, or between executes.

Currently, metadata of *every* prepared statement will be checksummed,
and change is detected once checksum changes.

This is not from ideal, performance-wise. The code for
better/faster detection of unchanged metadata, is already in place, but
currently disabled due to PS bugs, such as MDEV-23913.

Since commit 30ea63b7
we actually depend on futex on Linux. Also, we depend on
std::atomic for even longer.