gevent
– common functions#
The most common functions and classes are available in the
gevent
top level package.
Please read Introduction for an introduction to the concepts discussed here.
See also
See also
For configuring gevent using the environment or the
gevent.config
object.
- __version__ = '24.2.2.dev0'#
The human-readable PEP 440 version identifier. Use
pkg_resources.parse_version(__version__)
orpackaging.version.Version(__version__)
to get a machine-usable value.
Working With Greenlets#
See gevent.Greenlet
for more information about greenlet
objects.
Creating Greenlets#
- spawn(function, *args, **kwargs) Greenlet #
Create a new
Greenlet
object and schedule it to runfunction(*args, **kwargs)
. This can be used asgevent.spawn
orGreenlet.spawn
.The arguments are passed to
Greenlet.__init__()
.Changed in version 1.1b1: If a function is given that is not callable, immediately raise a
TypeError
instead of spawning a greenlet that will raise an uncaught TypeError.
- spawn_later(seconds, function, *args, **kwargs) Greenlet #
Create and return a new
Greenlet
object scheduled to runfunction(*args, **kwargs)
in a future loop iteration seconds later. This can be used asGreenlet.spawn_later
orgevent.spawn_later
.The arguments are passed to
Greenlet.__init__()
.Changed in version 1.1b1: If an argument that’s meant to be a function (the first argument in args, or the
run
keyword ) is given to this classmethod (and not a classmethod of a subclass), it is verified to be callable. Previously, the spawned greenlet would have failed when it started running.
- spawn_raw(function, *args, **kwargs)[source]#
Create a new
greenlet.greenlet
object and schedule it to runfunction(*args, **kwargs)
.This returns a raw
greenlet
which does not have all the useful methods thatgevent.Greenlet
has. Typically, applications should preferspawn()
, but this method may occasionally be useful as an optimization if there are many greenlets involved.Changed in version 1.1a3: Verify that
function
is callable, raising a TypeError if not. Previously, the spawned greenlet would have failed the first time it was switched to.Changed in version 1.1b1: If function is not callable, immediately raise a
TypeError
instead of spawning a greenlet that will raise an uncaught TypeError.Changed in version 1.1rc2: Accept keyword arguments for
function
as previously (incorrectly) documented. Note that this may incur an additional expense.Changed in version 1.3a2: Populate the
spawning_greenlet
andspawn_tree_locals
attributes of the returned greenlet.Changed in version 1.3b1: Only populate
spawning_greenlet
andspawn_tree_locals
ifGEVENT_TRACK_GREENLET_TREE
is enabled (the default). If not enabled, those attributes will not be set.Changed in version 1.5a3: The returned greenlet always has a loop attribute matching the current hub’s loop. This helps it work better with more gevent APIs.
Getting Greenlets#
- getcurrent()#
Return the currently executing greenlet (the one that called this function). Note that this may be an instance of
Greenlet
orgreenlet.greenlet
.
Stopping Greenlets#
- kill(greenlet, exception=GreenletExit)[source]#
Kill greenlet asynchronously. The current greenlet is not unscheduled.
Note
The method
Greenlet.kill()
method does the same and more (and the same caveats listed there apply here). However, the MAIN greenlet - the one that exists initially - does not have akill()
method, and neither do any created withspawn_raw()
, so you have to use this function.Caution
Use care when killing greenlets. If they are not prepared for exceptions, this could result in corrupted state.
Changed in version 1.1a2: If the
greenlet
has akill
method, calls it. This prevents a greenlet from being switched to for the first time after it’s been killed but not yet executed.
- killall(greenlets, exception=GreenletExit, block=True, timeout=None)[source]#
Forceably terminate all the greenlets by causing them to raise exception.
Caution
Use care when killing greenlets. If they are not prepared for exceptions, this could result in corrupted state.
- Parameters:
greenlets – A bounded iterable of the non-None greenlets to terminate. All the items in this iterable must be greenlets that belong to the same hub, which should be the hub for this current thread. If this is a generator or iterator that switches greenlets, the results are undefined.
exception – The type of exception to raise in the greenlets. By default this is
GreenletExit
.block (bool) – If True (the default) then this function only returns when all the greenlets are dead; the current greenlet is unscheduled during that process. If greenlets ignore the initial exception raised in them, then they will be joined (with
gevent.joinall()
) and allowed to die naturally. If False, this function returns immediately and greenlets will raise the exception asynchronously.timeout (float) – A time in seconds to wait for greenlets to die. If given, it is only honored when
block
is True.
- Raises:
Timeout – If blocking and a timeout is given that elapses before all the greenlets are dead.
Changed in version 1.1a2: greenlets can be any iterable of greenlets, like an iterator or a set. Previously it had to be a list or tuple.
Changed in version 1.5a3: Any
Greenlet
in the greenlets list that hadn’t been switched to before calling this method will never be switched to. This makes this function behave likeGreenlet.kill()
. This does not apply to raw greenlets.Changed in version 1.5a3: Now accepts raw greenlets created by
gevent.spawn_raw()
.
Sleeping#
- sleep(seconds=0, ref=True)[source]#
Put the current greenlet to sleep for at least seconds.
seconds may be specified as an integer, or a float if fractional seconds are desired.
Tip
In the current implementation, a value of 0 (the default) means to yield execution to any other runnable greenlets, but this greenlet may be scheduled again before the event loop cycles (in an extreme case, a greenlet that repeatedly sleeps with 0 can prevent greenlets that are ready to do I/O from being scheduled for some (small) period of time); a value greater than 0, on the other hand, will delay running this greenlet until the next iteration of the loop.
If ref is False, the greenlet running
sleep()
will not preventgevent.wait()
from exiting.Changed in version 1.3a1: Sleeping with a value of 0 will now be bounded to approximately block the loop for no longer than
gevent.getswitchinterval()
.See also
- idle(priority=0)[source]#
Cause the calling greenlet to wait until the event loop is idle.
Idle is defined as having no other events of the same or higher priority pending. That is, as long as sockets, timeouts or even signals of the same or higher priority are being processed, the loop is not idle.
See also
Switching#
- getswitchinterval() current switch interval #
-
New in version 1.3.
- setswitchinterval(seconds)#
Set the approximate maximum amount of time that callback functions will be allowed to run before the event loop is cycled to poll for events. This prevents code that does things like the following from monopolizing the loop:
while True: # Burning CPU! gevent.sleep(0) # But yield to other greenlets
Prior to this, this code could prevent the event loop from running.
On Python 3, this uses the native
sys.setswitchinterval()
andsys.getswitchinterval()
.New in version 1.3.
Waiting#
- wait(objects=None, timeout=None, count=None)#
Wait for objects to become ready or for event loop to finish.
If objects is provided, it must be a list containing objects implementing the wait protocol (rawlink() and unlink() methods):
gevent.Greenlet
instancegevent.event.Event
instancegevent.lock.Semaphore
instancegevent.subprocess.Popen
instance
If objects is
None
(the default),wait()
blocks until the current event loop has nothing to do (or until timeout passes):all greenlets have finished
all servers were stopped
all event loop watchers were stopped.
If count is
None
(the default), wait for all objects to become ready.If count is a number, wait for (up to) count objects to become ready. (For example, if count is
1
then the function exits when any object in the list is ready).If timeout is provided, it specifies the maximum number of seconds
wait()
will block.Returns the list of ready objects, in the order in which they were ready.
See also
- iwait(objects, timeout=None, count=None)#
Iteratively yield objects as they are ready, until all (or count) are ready or timeout expired.
If you will only be consuming a portion of the objects, you should do so inside a
with
block on this object to avoid leaking resources:with gevent.iwait((a, b, c)) as it: for i in it: if i is a: break
- Parameters:
objects – A sequence (supporting
len()
) containing objects implementing the wait protocol (rawlink() and unlink()).count (int) – If not
None
, then a number specifying the maximum number of objects to wait for. IfNone
(the default), all objects are waited for.timeout (float) – If given, specifies a maximum number of seconds to wait. If the timeout expires before the desired waited-for objects are available, then this method returns immediately.
See also
Changed in version 1.1a1: Add the count parameter.
Changed in version 1.1a2: No longer raise
LoopExit
if our caller switches greenlets in between items yielded by this function.Changed in version 1.4: Add support to use the returned object as a context manager.
Working with multiple processes#
Note
These functions will only be available if os.fork()
is
available. In general, prefer to use gevent.os.fork()
instead
of manually calling these functions.
- fork(*args, **kwargs)[source]#
Forks a child process and starts a child watcher for it in the parent process so that
waitpid
and SIGCHLD work as expected.This implementation of
fork
is a wrapper forfork_and_watch()
when the environment variableGEVENT_NOWAITPID
is not defined. This is the default and should be used by most applications.Changed in version 1.1b2.
- reinit() None [source]#
Prepare the gevent hub to run in a new (forked) process.
This should be called immediately after
os.fork()
in the child process. This is done automatically bygevent.os.fork()
or if theos
module has been monkey-patched. If this function is not called in a forked process, symptoms may include hanging of functions likesocket.getaddrinfo()
, and the hub’s threadpool is unlikely to work.Note
Registered fork watchers may or may not run before this function (and thus
gevent.os.fork
) return. If they have not run, they will run “soon”, after an iteration of the event loop. You can force this by inserting a few small (but non-zero) calls tosleep()
after fork returns. (As of gevent 1.1 and before, fork watchers will not have run, but this may change in the future.)Note
This function may be removed in a future major release if the fork process can be more smoothly managed.
Warning
See remarks in
gevent.os.fork()
about greenlets and event loop watchers in the child process.
Signals#
- signal_handler(signalnum, handler, *args, **kwargs) object #
Call the handler with the args and kwargs when the process receives the signal signalnum.
The handler will be run in a new greenlet when the signal is delivered.
This returns an object with the useful method
cancel
, which, when called, will prevent future deliveries of signalnum from calling handler. It’s best to keep the returned object alive until you callcancel
.Note
This may not operate correctly with
SIGCHLD
if libev child watchers are used (as they are by default withgevent.os.fork
). Seegevent.signal
for a more general purpose solution.Changed in version 1.2a1: The
handler
argument is required to be callable at construction time.Changed in version 20.5.1: The
cancel
method now properly cleans up all native resources, and drops references to all the arguments of this function.
Timeouts#
See class gevent.Timeout
for information about Timeout objects.
- with_timeout(seconds, function, *args, **kwds)[source]#
Wrap a call to function with a timeout; if the called function fails to return before the timeout, cancel it and return a flag value, provided by timeout_value keyword argument.
If timeout expires but timeout_value is not provided, raise
Timeout
.Keyword argument timeout_value is not passed to function.