diff --git a/docs/source/_static/nursery-start-readiness.png b/docs/source/_static/nursery-start-readiness.png new file mode 100644 index 000000000..e74d341c2 Binary files /dev/null and b/docs/source/_static/nursery-start-readiness.png differ diff --git a/docs/source/_static/nursery-start-readiness.svg b/docs/source/_static/nursery-start-readiness.svg new file mode 100644 index 000000000..5ccea2605 --- /dev/null +++ b/docs/source/_static/nursery-start-readiness.svg @@ -0,0 +1,98 @@ + +Embedded inter font subsets retain the following copyright and SIL OFL 1.1 license. The surrounding diagram retains its repository license. + +Copyright 2016 The Inter Project Authors (https://github.com/rsms/inter) Inter-Italic[opsz,wght].ttf: Copyright 2016 The Inter Project Authors (https://github.com/rsms/inter) + +This Font Software is licensed under the SIL Open Font License, Version 1.1. +This license is copied below, and is also available with a FAQ at: +http://scripts.sil.org/OFL + + +----------------------------------------------------------- +SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007 +----------------------------------------------------------- + +PREAMBLE +The goals of the Open Font License (OFL) are to stimulate worldwide +development of collaborative font projects, to support the font creation +efforts of academic and linguistic communities, and to provide a free and +open framework in which fonts may be shared and improved in partnership +with others. + +The OFL allows the licensed fonts to be used, studied, modified and +redistributed freely as long as they are not sold by themselves. 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The requirement for fonts to +remain under this license does not apply to any document created +using the Font Software. + +TERMINATION +This license becomes null and void if any of the above conditions are +not met. + +DISCLAIMER +THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, +EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF +MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT +OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE +COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, +INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL +DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING +FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM +OTHER DEALINGS IN THE FONT SOFTWARE. + +Trio service startup readiness handshake with nursery.startThe parent awaits nursery.start for a trio.serve_tcp child. The child binds listening sockets, then calls task_status.started(listeners). Only then does the parent receive the listeners and connect to a returned port. The child continues serving after the readiness signal.await nursery.start(serve)Bind and listenListening sockets readystarted(listeners)Connect to returned portTCP connection establishedParent taskWaits for started()Service child taskRuns trio.serve_tcpListening socketBound and listening diff --git a/docs/source/reference-core.rst b/docs/source/reference-core.rst index ee4468ce6..36a13bf0a 100644 --- a/docs/source/reference-core.rst +++ b/docs/source/reference-core.rst @@ -1022,6 +1022,34 @@ The nursery API .. automethod:: start_soon(async_fn, *args, name = None) +Service startup readiness ++++++++++++++++++++++++++ + +:meth:`Nursery.start` waits for a readiness signal, rather than merely scheduling +another task or waiting for that task to finish. For example, +:func:`serve_tcp` binds its listening sockets before it signals +``task_status.started(listeners)``. The awaiting parent receives those listeners +and can connect to their bound ports, while the service task continues running. + +.. figure:: _static/nursery-start-readiness.png + :alt: The parent awaits nursery.start for a serve_tcp child. The child binds listening sockets and signals started(listeners). The parent then receives the listeners and connects to a returned port. The service continues running after signaling readiness. + :width: 760px + + Successful TCP service startup. :download:`Editable SVG <_static/nursery-start-readiness.svg>`. + `Edit diagram `__. + +The child's code defines what "ready" means. A call to ``started()`` is not a +promise that the service has finished, nor that every application-level handler +has already run. In this example it tells the parent that listening sockets are +available. By contrast, :meth:`Nursery.start_soon` returns without waiting for +this handshake. + +If the child raises before signaling readiness, that exception is reported by +the awaiting ``start`` call. If it exits normally without calling ``started()``, +``start`` raises :class:`RuntimeError`. Cancelling ``start`` during startup also +cancels the child. After the signal, the child belongs to the nursery and its +subsequent errors follow the nursery's usual exception handling. + .. attribute:: TASK_STATUS_IGNORED :type: TaskStatus diff --git a/newsfragments/3540.doc.rst b/newsfragments/3540.doc.rst new file mode 100644 index 000000000..27c409b84 --- /dev/null +++ b/newsfragments/3540.doc.rst @@ -0,0 +1 @@ +Added a service startup readiness diagram and explanation for ``Nursery.start``.