This patch makes box.error() always promote error to the diagnostic
area despite of passed arguments.

Closes #4829

@TarantoolBot document
Title: always promote error created via box.error() to diag

box.error() is able to accept two types of argument: either pair of code
and reason (box.error{code = 555, reason = 'Arbitrary message'}) or error
object (box.error(err)). In the first case error is promoted to
diagnostic area, meanwhile in the latter - it is not:
```
e1 = box.error.new({code = 111, reason = "cause"})
box.error({code = 111, reason = "err"})
- error: err
box.error.last()
- err
box.error(e1)
- error: cause
box.error.last()
- err
```
From now box.error(e1) sets error to diagnostic area as well:
```
box.error(e1)
- error: cause
box.error.last()
- cause
```

Refactor iproto_reply_error and iproto_write_error with a new
mpstream-based helper mpstream_iproto_encode_error that encodes
error object for iproto protocol on a given stream object.
Previously each routine implemented an own error encoding, but
with the increasing complexity of encode operation with following
patches we need a uniform way to do it.

The iproto_write_error routine starts using region location
to use region-based mpstream. It is not a problem itself, because
errors reporting is not really performance-critical path.

Needed for #1148

Since we've introduced stacked diagnostic in previous commit, let's use
it in the code implementing functional indexes.

Part of #1148

In terms of implementation, now struct error objects can be organized
into double-linked lists. To achieve this pointers to the next and
previous elements (cause and effect correspondingly) have been added to
struct error. It is worth mentioning that already existing rlist and
stailq list implementations are not suitable: rlist is cycled list, as a
result it is impossible to start iteration over the list from random
list entry and finish it at the logical end of the list; stailq is
single-linked list leaving no possibility to remove elements from the
middle of the list.

As a part of C interface, box_error_add() has been introduced. In
contrast to box_error_set() it does not replace last raised error, but
instead it adds error to the list of diagnostic errors having already
been set. If error is to be deleted (its reference counter hits 0 value)
it is unlinked from the list it belongs to and destroyed. Meanwhile,
error destruction leads to decrement of reference counter of its
previous error and so on.

To organize errors into lists in Lua, table representing error object in
Lua now has .prev field (corresponding to 'previous' error) and method
:set_prev(e). The latter accepts error object (i.e. created via
box.error.new() or box.error.last()) and nil value. Both field .prev and
:set_prev() method are implemented as ffi functions. Also note that
cycles are not allowed while organizing errors into lists:
e1 -> e2 -> e3; e3:set_prev(e1) -- would lead to error.

Part of #1148

To achieve this let's refactor luaT_error_create() to return error
object instead of setting it via box_error_set().
luaT_error_create() is used both to handle box.error() and
box.error.new() invocations, and box.error() is still expected to set
error to diagnostic area. So, luaT_error_call() which implements
box.error() processing at the end calls diag_set_error().
It is worth mentioning that net.box module relied on the fact that
box.error.new() set error to diagnostic area: otherwise request errors
don't get to diagnostic area on client side.

Needed for #1148
Closes #4778

@TarantoolBot document
Title: Don't promote error created via box.error.new to diagnostic area

Now box.error.new() only creates error object, but doesn't set it to
Tarantool's diagnostic area:
```
box.error.clear()
e = box.error.new({code = 111, reason = "cause"})
assert(box.error.last() == nil)
---
- true
...
```
To set error in diagnostic area explicitly box.error.set() has been
introduced. It accepts error object which is set as last system error
(i.e. becomes available via box.error.last()).
Finally, box.error.new() does not longer accept error object as an
argument (this was undocumented feature).
Note that patch does not affect box.error(), which still pushes error to
diagnostic area. This fact is reflected in docs:
'''
Emulate a request error, with text based on one of the pre-defined
Tarantool errors...
'''

File descriptor was set to -1 regardless of whether
the object was closed properly. As a result, in case
of an error the descriptor would leak.

GC finalizer of a descriptor is left intact not to
overcomplicate it.

swim object created a new fiber in its GC function, because C
function swim_delete() yields, and can't be called from an ffi.gc
hook.

It is not needed since the fiber module has a single worker
exactly for such cases. The patch uses it.

Follow up #4727

Fio.open() returned a file descriptor, which was not closed
automatically after all its links were nullified. In other words,
GC didn't close the descriptor.

This was not really useful, because after fio.open() an exception
may appear, and user needed to workaround this to manually call
fio_object:close(). Also this was not consistent with io.open().

Now fio.open() object closes the descriptor automatically when
GCed.

Closes #4727

@TarantoolBot document
Title: fio descriptor is closed automatically by GC

fio.open() returns a descriptor which can be closed manually by
calling :close() method, or it will be closed automatically, when
it has no references, and GC deletes it.

:close() method existed always, auto GC was added just now.

Keep in mind, that the number of file descriptors is limited, and
they can end earlier than GC will be triggered to collect not
used descriptors. It is always better to close them manually as
soon as possible.

fiber._internal.schedule_task() is an API for a singleton fiber
worker object. It serves for not urgent delayed execution of
functions. Main purpose - schedule execution of a function, which
is going to yield, from a context, where a yield is not allowed.
Such as an FFI object's GC callback.

It will be used by SWIM and by fio, whose destruction yields, but
they need to use GC finalizer, where a yield is not allowed.

Part of #4727

box.error.set(err) sets err to instance's diagnostics area. Argument err
is supposed to be instance of error object. This method is required
since we are going to avoid adding created via box.error.new() errors to
Tarantool's diagnostic area.

Needed for #1148
Part of #4778

Let's rename diag_add_error() to diag_set_error() because it actually
replaces an error object in diagnostic area with a new one and this name
is not representative. Moreover, we are going to introduce a new
diag_add_error() which will place error at the top of stack diagnostic
area.

Needed for #1148

In case of direct execute without using a shell there
is no need to require a caller to allocate redundant
space, lets pass executable name in first argument.

Since this is yet testing api we're allowed to change
without breaking aything.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

SO_LINGER makes no much sense for unix-sockets, and Microsoft WSL
is returning EINVAL if setsockopts called for SO_LINGER over unix
sockets:

  [004] 2020-03-11 18:42:29.592 [29182] main/102/app sio.c:169 !> SystemError setsockopt(SO_LINGER), called on fd 16, aka
  [004] 2020-03-11 18:42:29.592 [29182] main/102/app F> can't initialize storage: setsockopt(SO_LINGER), called on fd 16,
  [004] 2020-03-11 18:42:29.592 [29182] main/102/app F> can't initialize storage: setsockopt(SO_LINGER), called on fd 16,

And it's sort of correct here, but the problem is Linux is simply
silently ignoring it, which passes tests.

After much debates we decided to work-around this case via CMAKE
define.

NB! In a future (April/May 2020), when WSL2 with full Linux kernel
would be released we should disable this check.

Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>

vy_build_insert_tuple() processes insertion into secondary indexes being
created. It contains yield points during which in-memory level of LSM
tree may change (for example rotate owing to triggered dump). So after
yield point it is required to fetch from LSM struct pointer to mem again
to operate on valid metadata. This patch updates pointer to mem after
mentioned yield point.

Closes #4810

Currently the journal provides only one method -- write,
which implies a callback to trigger upon write completion
(in contrary with 1.10 series where all commits were
processing in synchronous way).

Lets make difference between sync and async writes more
notable: provide journal::write_async method which runs
completion function once entry is written, in turn
journal:write handle transaction in synchronous way.

Redesing notes:

1) The callback for async write set once in journal
   creation. There is no need to carry callback in
   every journal entry. This allows us to save some
   memory;

2) txn_commit and txn_commit_async call txn_rollback
   where appropriate;

3) no need to call journal_entry_complete on sync
   writes anymore;

4) wal_write_in_wal_mode_none is too long, renamed
   to wal_write_none;

5) wal engine use async writes internally but it is
   transparent to callers.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

This makes code easier to read and allows to reuse
txn allocation in sync\async writes.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

Otherwise we won't be able to make a rollback in case
of journal_entry_new allocation failure.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

We gonna diverge sync and async code flow thus lets
make txn_commit to not use txn_commit_async.

Fixes #4776

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

We will use this function inside wal engine right
after journal redesign is complete.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

To reuse in sync trancastion once journal
redesign is complete.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

For unification sake, we will handle nop transactions
via common helper for both sync and async cases.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

To reflect the fact tha we're don't waiting for
transaction to complete but rely on completion
callback.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

We already have a "get" function in this header which is
named in_txt(). Having both get/set in one place should
be more consistent.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

There is no need for several instances of
recovery journal variable. Lets make it
statically allocated inside recovery_journal_create
routine.

And drop the inline annotation because there is
absolutely no need for this routine being inline.

Suggested-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

Allows to eliminate code duplication.

Acked-by: Konstantin Osipov <kostja.osipov@gmail.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

box_check_config() didn't check memtx_memory and vinyl_memory
upper bound. As a result, it was possible to set memory size
higher than what the quota allows as maximum.

That worked only when box.cfg() was called first time, because
quota_init() does not check its value. Subsequent box.cfg() calls
use quota_set(), which aborts the program if a size is too big.
Only in debug mode. In release quota_set() also worked with any
sizes.

Closes #4705

Reviewed-by: Igor Munkin <imun@tarantool.org>
Reviewed-by: Nikita Pettik <korablev@tarantool.org>

It was calling box_check_sql_cache_size() assuming that it
throws. But it returns 0/-1.

Reviewed-by: Igor Munkin <imun@tarantool.org>
Reviewed-by: Nikita Pettik <korablev@tarantool.org>

Use bit_count_u32() instead of plain __builtin_popcount() for filter
size, just as we do for vclock size now.

We're using an unsigned int to hold vclock map, but there is no
guarantee that unsigned int will be 4 bytes in size to fit all the 32
vclock components. So use uint32_t instead and add an alias to it
vclock_map_t.

We need to set a thread cancellation guard, because
another thread may cancel the current thread at a
really bad time (messages flush, mutex lock)

Fixes: #4127

Users keep complaining about too short fiber name. New limit is
255, should be enough for any sane name.

Closes #4394

Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Nikita Pettik <korablev@tarantool.org>

@TarantoolBot document
Title: fiber.name length limit.

It was 32, now it is 255. Besides, it seems like `fiber.name`
`{truncate = true}` option is not documented.

By default, if a new name is too long, `fiber.name(new_name)`
fails with an exception. To make it always succeed there is an
option 'truncate': `fiber.name(new_name, {truncate = true})`. It
truncates the name to the max length if it is too long.

Box.cfg{listen = 0} automatically chooses a port. But it was
impossible to obtain a real port the instance is bound to.

An ability to see a real port may help to make test-run more
robust, because it won't depend on which ports are free, and
won't need to pre-choose them in advance.

Now box.info.listen shows a real address, or nil when listen is
turned off. Also a real address is logged instead of the dummy
0-port one.

Closes #4620

@TarantoolBot document
Title: box.info.listen - real address

New value in box.info - listen. It is a real address to which the
instance was bound. For example, if box.cfg.listen was set with
a zero port, box.info.listen will show a real port. The address
is stored as a string:

    - unix/:<path> for UNIX domain sockets;
    - <ip>:<port> for IPv4;
    - [ip]:<port> for IPv6.

If the instance does not listen anything, box.info.listen is nil.

This patch introduces "current" function for sequences.
It returns the last retrieved value of specified sequence or
throws an error if no value has been generated yet.

This patch partially reverts 3ff1f1e3
(box: remove sequence_get) here similar function "get" was removed
to avoid possible misleading with "currval" function of PosgreSQL
that returns the last obtained value of the sequence in the scope
of current session. In contrast "current" returns the last globally
retrieved value of the sequence.

Closes #4752

Reviewed-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Reviewed-by: Nikita Pettik <korablev@tarantool.org>

@TarantoolBot document
Title: sequence:current()

This patch introduces "current" function for sequences.
It returns the last retrieved value of specified sequence or
throws an error if no value has been generated yet ("next"
has not been called yet or right after "reset" is called).

Lua:

Example:

```lua
sq = box.schema.sequence.create('test')
---
...
sq:current()
---
- error: Sequence 'test' is not started
...
sq:next()
---
- 1
...
sq:current()
---
- 1
...
sq:set(42)
---
...
sq:current()
---
- 42
...
sq:reset()
---
...
sq:current()  -- error
---
- error: Sequence 'test' is not started
...
```

C API:

```C
int
box_sequence_current(uint32_t seq_id, int64_t *result);
```

Where:
  * seq_id - sequence identifier;
  * result - pointer to a variable where the current sequence
  value will be stored on success.

Returns 0 on success and -1 otherwise. In case of an error user
could get it via `box_error_last()`.

Absence of the body in the unprepare response forces users to perform
additional checks to avoid errors. Adding an empty body fixes this problem.

Closes #4769

Reviewed-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Reviewed-by: Nikita Pettik <korablev@tarantool.org>

In #4684 it was found that box.tuple.* contained some private
functions: bless(), encode(), and is().

Bless() and encode() didn't make any sense for a user, so they
were hidden into box.internal.tuple.*.

But box.tuple.is() is actually a useful thing. It is harnessed in
the tests a lot, and is likely to be already used by customers,
because it is available in box.tuple.* for a long time. It is a
matter of time when someone will open a doc ticket saying that
box.tuple.is() is not documented. The patch makes it legally
public.

Follow-up #4684

@TarantoolBot document
Title: box.tuple.is()
```Lua
box.tuple.is(object)
```
A function to check whether a given object is a tuple cdata
object. Returns true or false. Never raises nor returns an error.

box.tuple.bless, .encode, and .is are internal. Their
behaviour is not documented, and they may omit some checks for the
sake of speed, and can crash if used without thinking.

Nonetheless, despite they are not documented, curious users could
notice them in box.tuple.* output via autocompletion, for example.
And they could try to use them. This is not ok.

box.tuple.bless() being called by a user leads either to a crash,
or to a leak (because it is basically tuple reference counter
increment).

box.tuple.encode() is kind of a wrapper around msgpack, and users
should not touch it. It may change, may be removed. And is just
makes no sense except some rare cases in schema.lua.

bless() and encode() were used in schema.lua only, so the patch
simply moves them to box.internal.tuple.

box.tuple.is() is kept as is, because
- this is used in the tests a lot;
- it is totally safe;
- that function actually makes sense, and some users could have
  already started using it.

There is no a test, since nothing to test - bless() is not
available for users anymore (assuming no one is brave enough to
rely on box.internal).

Closes #4684

Due to os specifics we can't call setsid after vfork on macos
(vfork is not longer a part of posix btw). Instead we can use
ioctl to clear the session, then initiate a new process group.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

This helps to identify if something gone
wrong inside a child process.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>