tornado.ioloop
— Main event loop¶
An I/O event loop for non-blocking sockets.
Typical applications will use a single IOLoop
object, in the
IOLoop.instance
singleton. The IOLoop.start
method should usually
be called at the end of the main()
function. Atypical applications may
use more than one IOLoop
, such as one IOLoop
per thread, or per unittest
case.
In addition to I/O events, the IOLoop
can also schedule time-based events.
IOLoop.add_timeout
is a non-blocking alternative to time.sleep
.
IOLoop objects¶
-
class
tornado.ioloop.
IOLoop
[source]¶ A level-triggered I/O loop.
We use
epoll
(Linux) orkqueue
(BSD and Mac OS X) if they are available, or else we fall back on select(). If you are implementing a system that needs to handle thousands of simultaneous connections, you should use a system that supports eitherepoll
orkqueue
.Example usage for a simple TCP server:
import errno import functools import ioloop import socket def connection_ready(sock, fd, events): while True: try: connection, address = sock.accept() except socket.error, e: if e.args[0] not in (errno.EWOULDBLOCK, errno.EAGAIN): raise return connection.setblocking(0) handle_connection(connection, address) sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) sock.setblocking(0) sock.bind(("", port)) sock.listen(128) io_loop = ioloop.IOLoop.instance() callback = functools.partial(connection_ready, sock) io_loop.add_handler(sock.fileno(), callback, io_loop.READ) io_loop.start()
Running an IOLoop¶
-
static
IOLoop.
current
()[source]¶ Returns the current thread’s
IOLoop
.If an
IOLoop
is currently running or has been marked as current bymake_current
, returns that instance. Otherwise returnsIOLoop.instance()
, i.e. the main thread’sIOLoop
.A common pattern for classes that depend on
IOLoops
is to use a default argument to enable programs with multipleIOLoops
but not require the argument for simpler applications:class MyClass(object): def __init__(self, io_loop=None): self.io_loop = io_loop or IOLoop.current()
In general you should use
IOLoop.current
as the default when constructing an asynchronous object, and useIOLoop.instance
when you mean to communicate to the main thread from a different one.
-
IOLoop.
make_current
()[source]¶ Makes this the
IOLoop
for the current thread.An
IOLoop
automatically becomes current for its thread when it is started, but it is sometimes useful to callmake_current
explictly before starting theIOLoop
, so that code run at startup time can find the right instance.
-
static
IOLoop.
instance
()[source]¶ Returns a global
IOLoop
instance.Most applications have a single, global
IOLoop
running on the main thread. Use this method to get this instance from another thread. To get the current thread’sIOLoop
, usecurrent()
.
-
IOLoop.
install
()[source]¶ Installs this
IOLoop
object as the singleton instance.This is normally not necessary as
instance()
will create anIOLoop
on demand, but you may want to callinstall
to use a custom subclass ofIOLoop
.
-
IOLoop.
start
()[source]¶ Starts the I/O loop.
The loop will run until one of the callbacks calls
stop()
, which will make the loop stop after the current event iteration completes.
-
IOLoop.
stop
()[source]¶ Stop the I/O loop.
If the event loop is not currently running, the next call to
start()
will return immediately.To use asynchronous methods from otherwise-synchronous code (such as unit tests), you can start and stop the event loop like this:
ioloop = IOLoop() async_method(ioloop=ioloop, callback=ioloop.stop) ioloop.start()
ioloop.start()
will return afterasync_method
has run its callback, whether that callback was invoked before or afterioloop.start
.Note that even after
stop
has been called, theIOLoop
is not completely stopped untilIOLoop.start
has also returned. Some work that was scheduled before the call tostop
may still be run before theIOLoop
shuts down.
-
IOLoop.
run_sync
(func, timeout=None)[source]¶ Starts the
IOLoop
, runs the given function, and stops the loop.If the function returns a
Future
, theIOLoop
will run until the future is resolved. If it raises an exception, theIOLoop
will stop and the exception will be re-raised to the caller.The keyword-only argument
timeout
may be used to set a maximum duration for the function. If the timeout expires, aTimeoutError
is raised.This method is useful in conjunction with
tornado.gen.coroutine
to allow asynchronous calls in amain()
function:@gen.coroutine def main(): # do stuff... if __name__ == '__main__': IOLoop.instance().run_sync(main)
-
IOLoop.
close
(all_fds=False)[source]¶ Closes the
IOLoop
, freeing any resources used.If
all_fds
is true, all file descriptors registered on the IOLoop will be closed (not just the ones created by theIOLoop
itself).Many applications will only use a single
IOLoop
that runs for the entire lifetime of the process. In that case closing theIOLoop
is not necessary since everything will be cleaned up when the process exits.IOLoop.close
is provided mainly for scenarios such as unit tests, which create and destroy a large number ofIOLoops
.An
IOLoop
must be completely stopped before it can be closed. This means thatIOLoop.stop()
must be called andIOLoop.start()
must be allowed to return before attempting to callIOLoop.close()
. Therefore the call toclose
will usually appear just after the call tostart
rather than near the call tostop
.Changed in version 3.1: If the
IOLoop
implementation supports non-integer objects for “file descriptors”, those objects will have theirclose
method whenall_fds
is true.
I/O events¶
Callbacks and timeouts¶
-
IOLoop.
add_callback
(callback, *args, **kwargs)[source]¶ Calls the given callback on the next I/O loop iteration.
It is safe to call this method from any thread at any time, except from a signal handler. Note that this is the only method in
IOLoop
that makes this thread-safety guarantee; all other interaction with theIOLoop
must be done from thatIOLoop
‘s thread.add_callback()
may be used to transfer control from other threads to theIOLoop
‘s thread.To add a callback from a signal handler, see
add_callback_from_signal
.
-
IOLoop.
add_callback_from_signal
(callback, *args, **kwargs)[source]¶ Calls the given callback on the next I/O loop iteration.
Safe for use from a Python signal handler; should not be used otherwise.
Callbacks added with this method will be run without any
stack_context
, to avoid picking up the context of the function that was interrupted by the signal.
-
IOLoop.
add_future
(future, callback)[source]¶ Schedules a callback on the
IOLoop
when the givenFuture
is finished.The callback is invoked with one argument, the
Future
.
-
IOLoop.
add_timeout
(deadline, callback)[source]¶ Runs the
callback
at the timedeadline
from the I/O loop.Returns an opaque handle that may be passed to
remove_timeout
to cancel.deadline
may be a number denoting a time (on the same scale asIOLoop.time
, normallytime.time
), or adatetime.timedelta
object for a deadline relative to the current time.Note that it is not safe to call
add_timeout
from other threads. Instead, you must useadd_callback
to transfer control to theIOLoop
‘s thread, and then calladd_timeout
from there.
-
IOLoop.
remove_timeout
(timeout)[source]¶ Cancels a pending timeout.
The argument is a handle as returned by
add_timeout
. It is safe to callremove_timeout
even if the callback has already been run.
-
IOLoop.
time
()[source]¶ Returns the current time according to the
IOLoop
‘s clock.The return value is a floating-point number relative to an unspecified time in the past.
By default, the
IOLoop
‘s time function istime.time
. However, it may be configured to use e.g.time.monotonic
instead. Calls toadd_timeout
that pass a number instead of adatetime.timedelta
should use this function to compute the appropriate time, so they can work no matter what time function is chosen.
-
class
tornado.ioloop.
PeriodicCallback
(callback, callback_time, io_loop=None)[source]¶ Schedules the given callback to be called periodically.
The callback is called every
callback_time
milliseconds.start
must be called after thePeriodicCallback
is created.
Debugging and error handling¶
-
IOLoop.
handle_callback_exception
(callback)[source]¶ This method is called whenever a callback run by the
IOLoop
throws an exception.By default simply logs the exception as an error. Subclasses may override this method to customize reporting of exceptions.
The exception itself is not passed explicitly, but is available in
sys.exc_info
.
-
IOLoop.
set_blocking_signal_threshold
(seconds, action)[source]¶ Sends a signal if the
IOLoop
is blocked for more thans
seconds.Pass
seconds=None
to disable. Requires Python 2.6 on a unixy platform.The action parameter is a Python signal handler. Read the documentation for the
signal
module for more information. Ifaction
is None, the process will be killed if it is blocked for too long.
-
IOLoop.
set_blocking_log_threshold
(seconds)[source]¶ Logs a stack trace if the
IOLoop
is blocked for more thans
seconds.Equivalent to
set_blocking_signal_threshold(seconds, self.log_stack)
-
IOLoop.
log_stack
(signal, frame)[source]¶ Signal handler to log the stack trace of the current thread.
For use with
set_blocking_signal_threshold
.