In commit 1fdc161d we introduced
a mutex-and-condition-variable based fallback implementation
for platforms that lack a futex system call. That implementation
is prone to hangs.

Let us use separate condition variables for shared and exclusive requests.

The clang++ -stdlib=libc++ header file <fstream> depends on
<filesystem> that defines a member function path::root_name(),
which conflicts with the rather unused #define root_name()
that had been introduced in
commit 7c58e97b.

Because an instrumented -stdlib=libc++ (rather than the default
-stdlib=libstdc++) is easier to build for a working -fsanitize=memory
(cmake -DWITH_MSAN=ON), let us remove the conflicting #define for now.

Sorry, only tested commit 4174fc1a
on clang. Other compilers do not define __has_feature().

For some reason, commit 5bb5d4ad
made clang++-11 unhappy about a constexpr declaration.

For some reason, the test was never adjusted for
commit e6a50e41.

The Galera tests were massively failing with debug assertions.

Post-push Windows compilation errors fix.

Change thd->mdl_context.release_transactional_locks() to
thd->mdl_release_transactional_locks()

row_undo_ins_parse_undo_rec(): Do not try to read non-existing
virtual column information for the metadata record.

The replacement is buf_pool.contains_zip().

The new option --log-innodb-page-corruption is introduced.

When this option is set, backup is not interrupted if innodb corrupted
page is detected. Instead it logs all found corrupted pages in
innodb_corrupted_pages file in backup directory and finishes with error.

For incremental backup corrupted pages are also copied to .delta file,
because we can't do LSN check for such pages during backup,
innodb_corrupted_pages will also be created in incremental backup
directory.

During --prepare, corrupted pages list is read from the file just after
redo log is applied, and each page from the list is checked if it is allocated
in it's tablespace or not. If it is not allocated, then it is zeroed out,
flushed to the tablespace and removed from the list. If all pages are removed
from the list, then --prepare is finished successfully and
innodb_corrupted_pages file is removed from backup directory. Otherwise
--prepare is finished with error message and innodb_corrupted_pages contains
the list of the pages, which are detected as corrupted during backup, and are
allocated in their tablespaces, what means backup directory contains corrupted
innodb pages, and backup can not be considered as consistent.

For incremental --prepare corrupted pages from .delta files are applied
to the base backup, innodb_corrupted_pages is read from both base in
incremental directories, and the same action is proceded for corrupted
pages list as for full --prepare. innodb_corrupted_pages file is
modified or removed only in base directory.

If DDL happens during backup, it is also processed at the end of backup
to have correct tablespace names in innodb_corrupted_pages.

The reason for the failure is that
thd->mdl_context.release_transactional_locks()
was called after commit & rollback even in cases where the current
transaction is still active.

For 10.2, 10.3 and 10.4 the fix is simple:
- Replace all calls to thd->mdl_context.release_transactional_locks() with
  thd->release_transactional_locks(). The thd function will only call
  the mdl_context function if there are no active transactional locks.
  In 10.6 we will better fix where we will change the return value for
  some trans_xxx() functions to indicate if transaction did close the
  transaction or not. This will avoid the need of the indirect call.

Other things:
- trans_xa_commit() and trans_xa_rollback() will automatically
  call release_transactional_locks() if the transaction is closed.
- We can't do that for the other functions as the caller of many of these
  are doing additional work (like close_thread_tables) before calling
  release_transactional_locks().
- Added missing abort_result_set() and missing DBUG_RETURN in
  select_create::send_eof()
- Fixed wrong indentation in injector::transaction::commit()

The real fix for MDEV-15532 will be pushed into 10.2 and 10.6
This is an additional fix for 10.4.

In 10.4 trans_xa_detach was introduced.  However THD::cleanup() assumes
that after trans_xa_detach() is done, there is no registered transactions
anymore. In the 10.2 patch there will be an assert to ensure this, which
will cause 10.4 to fail.

The fix used is to reset the transaction flags in trans_xa_detach().

- the intention for my_getevents syscall is now better explained,
why are we using it (to be able to interrupt io_getevents syscall via
io_destroy()).

- Fix comment for MAX_EVENTS in getevent_thread_routine.
MAX_EVENTS is more of less arbitrary constant, chosen such that events array
is big enough to get multiple simultaneous io completions, but small
enough so it does not blow the thread's stack.

If maintenance timer does not do much for prolonged time, it will
wake up less frequently, once every 4 seconds instead of once every 0.4
second.

It will wakeup more often if thread creation is throttled, to avoid stalls.

For some reason, InnoDB debug tests on Windows fail due to rw_lock_t
if the function call overhead for some os_thread_ code is removed.

This change worked fine on Windows in combination with MDEV-24142.

MDEV-21265: IN predicate conversion to IN subquery should be allowed for a broader set of datatype comparison

Allow materialization strategy when collations on the
inner and outer sides of an IN subquery are the same and the
character set of the inner side is a proper subset of the character
set on the outer side.
This allows conversion from utf8mb3 to utf8mb4
as the former is a subset of the later.
This is only allowed when IN predicate is converted to an IN subquery

Backported part of the patch (d6a00d9b) of MDEV-17905.

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

Reviewed by:serg@mariadb.com