Module wspbus
source code
An implementation of the Web Site Process Bus.
This module is completely standalone, depending only on the stdlib.
Web Site Process Bus
--------------------
A Bus object is used to contain and manage site-wide behavior:
daemonization, HTTP server start/stop, process reload, signal handling,
drop privileges, PID file management, logging for all of these,
and many more.
In addition, a Bus object provides a place for each web framework
to register code that runs in response to site-wide events (like
process start and stop), or which controls or otherwise interacts with
the site-wide components mentioned above. For example, a framework which
uses file-based templates would add known template filenames to an
autoreload component.
Ideally, a Bus object will be flexible enough to be useful in a variety
of invocation scenarios:
1. The deployer starts a site from the command line via a framework-
neutral deployment script; applications from multiple frameworks
are mixed in a single site. Command-line arguments and configuration
files are used to define site-wide components such as the HTTP server,
WSGI component graph, autoreload behavior, signal handling, etc.
2. The deployer starts a site via some other process, such as Apache;
applications from multiple frameworks are mixed in a single site.
Autoreload and signal handling (from Python at least) are disabled.
3. The deployer starts a site via a framework-specific mechanism;
for example, when running tests, exploring tutorials, or deploying
single applications from a single framework. The framework controls
which site-wide components are enabled as it sees fit.
The Bus object in this package uses topic-based publish-subscribe
messaging to accomplish all this. A few topic channels are built in
('start', 'stop', 'exit', and 'graceful'). Frameworks and site containers
are free to define their own. If a message is sent to a channel that has
not been defined or has no listeners, there is no effect.
In general, there should only ever be a single Bus object per process.
Frameworks and site containers share a single Bus object by publishing
messages and subscribing listeners.
The Bus object works as a finite state machine which models the current
state of the process. Bus methods move it from one state to another;
those methods then publish to subscribed listeners on the channel for
the new state.
O
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V
STOPPING --> STOPPED --> EXITING -> X
A A |
| \___ |
| \ |
| V V
STARTED <-- STARTING
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_StateEnum
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Bus
Process state-machine and messenger for HTTP site deployment.
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states = _StateEnum()
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bus = cherrypy.engine
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