tarantool / tarantool / 37949096675

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Build Type

push

github

Committed by locker

Commit Message

box: move threads module out of experimental namespace

Follow-up #12207

@TarantoolBot document
Title: Document application threads

Application threads first appeared in Tarantool 3.7 as an experimental
feature. In Tarantool 3.9 it was moved out of the experimental namespace
and is now considered stable. The new feature allows application code
to use additional threads for offloading work off the main thread.
Like the main thread, each application thread runs an independent event
loop and a Lua interpreter and has most Tarantool built-in modules
available. However, usage of box features in application threads is
limited: it's impossible to directly write to the database and reads are
only possible via a read view.

To enable application threads, add the top-level section `threads` with
the sub-section `groups` to the configuration file. For example, to
create two application thread groups, `http` with one thread and `app`
with four threads, use the following config:

```yaml
threads:
  groups:
    - name: http
      size: 1
    - name: app
      size: 4
```

One can also configure application threads via the legacy `box.cfg`,
but it's possible to create only one thread group named `app`:

```lua
box.cfg{app_threads = 4}
```

The thread group `tx` with one thread is always created implicitly.
It can be used for calling the main thread from other threads, as
described below.

For interaction with application threads the `threads` Lua module was
introduced. The new module has the following functions:

 * `threads.export(func_name, func)`: exports a local Lua function so
   that it can be called with `threads.call()` from other threads.
 * `threads.call(group_name, func_name, args, opts)`: calls a function
   on a thread group. The function must be exported.
 * `threads.eval(group_name, expr, args, opts)`: executes a Lua
   expression on a thread group.
 * `threads.info()`: returns information about configured thread groups
   and the current thread (it... (continued)

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