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.. SPDX-License-Identifier: GPL-3.0-or-later
Timers and events reference
^^^^^^^^^^^^^^^^^^^^^^^^^^^
The timer represents exactly the thing described in the examples - it allows you to execute closures_
after specified time, or event recurrent events. Time is always described in milliseconds,
but there are convenient variables that you can use - ``sec, minute, hour``.
For example, ``5 * hour`` represents five hours, or 5*60*60*100 milliseconds.
.. function:: event.after(time, function)
:return: event id
Execute function after the specified time has passed.
The first parameter of the callback is the event itself.
Example:
.. code-block:: lua
event.after(1 * minute, function() print('Hi!') end)
.. function:: event.recurrent(interval, function)
:return: event id
Execute function immediately and then periodically after each ``interval``.
Example:
.. code-block:: lua
msg_count = 0
event.recurrent(5 * sec, function(e)
msg_count = msg_count + 1
print('Hi #'..msg_count)
end)
.. function:: event.reschedule(event_id, timeout)
Reschedule a running event, it has no effect on canceled events.
New events may reuse the event_id, so the behaviour is undefined if the function
is called after another event is started.
Example:
.. code-block:: lua
local interval = 1 * minute
event.after(1 * minute, function (ev)
print('Good morning!')
-- Halve the interval for each iteration
interval = interval / 2
event.reschedule(ev, interval)
end)
.. function:: event.cancel(event_id)
Cancel running event, it has no effect on already canceled events.
New events may reuse the event_id, so the behaviour is undefined if the function
is called after another event is started.
Example:
.. code-block:: lua
e = event.after(1 * minute, function() print('Hi!') end)
event.cancel(e)
Watch for file descriptor activity. This allows embedding other event loops or simply
firing events when a pipe endpoint becomes active. In another words, asynchronous
notifications for daemon.
.. function:: event.socket(fd, cb)
:param number fd: file descriptor to watch
:param cb: closure or callback to execute when fd becomes active
:return: event id
Execute function when there is activity on the file descriptor and calls a closure
with event id as the first parameter, status as second and number of events as third.
Example:
.. code-block:: lua
e = event.socket(0, function(e, status, nevents)
print('activity detected')
end)
e.cancel(e)
Asynchronous function execution
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The `event` package provides a very basic mean for non-blocking execution - it allows running code when activity on a file descriptor is detected, and when a certain amount of time passes. It doesn't however provide an easy to use abstraction for non-blocking I/O. This is instead exposed through the `worker` package (if `cqueues` Lua package is installed in the system).
.. function:: worker.coroutine(function)
Start a new coroutine with given function (closure). The function can do I/O or run timers without blocking the main thread. See cqueues_ for documentation of possible operations and synchronization primitives. The main limitation is that you can't wait for a finish of a coroutine from processing layers, because it's not currently possible to suspend and resume execution of processing layers.
Example:
.. code-block:: lua
worker.coroutine(function ()
for i = 0, 10 do
print('executing', i)
worker.sleep(1)
end
end)
.. function:: worker.sleep(seconds)
Pause execution of current function (asynchronously if running inside a worker coroutine).
Example:
.. code-block:: lua
function async_print(testname, sleep)
log(testname .. ': system time before sleep' .. tostring(os.time())
worker.sleep(sleep) -- other coroutines continue execution now
log(testname .. ': system time AFTER sleep' .. tostring(os.time())
end
worker.coroutine(function() async_print('call #1', 5) end)
worker.coroutine(function() async_print('call #2', 3) end)
Output from this example demonstrates that both calls to function ``async_print`` were executed asynchronously:
.. code-block:: none
call #2: system time before sleep 1578065073
call #1: system time before sleep 1578065073
call #2: system time AFTER sleep 1578065076
call #1: system time AFTER sleep 1578065078
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