Test2::Manual::Anatomy::Hubs(3pm)

NAME
Test2::Manual::Anatomy::Hubs - Internals documentation for the hub stack, and hubs.

DESCRIPTION
This document describes the hub stack, and the hubs it contains. It explains why we have a stack, and when to add/remove hubs from it.

WHAT IS A HUB?
Test2 is an event system, tools generate events, those events are then processed to modify the testing state (number of tests, number of failures, etc). The hub is responsible for receiving and processing events to record the change in state. All events should eventually reach a destination hub.

The base hub is Test2::Hub. All hub classes should inherit from the base hub class. The base hub class provides several hooks that allow you to monitor or modify events. Hubs are also responsible for forwarding events to the output formatter.

WHY DO WE HAVE A HUB STACK?
There are cases where it makes sense to have more than one hub:

subtests
    In Test2 subtests are implemented using the hub stack. When you start a subtest a new Test2::Hub::Subtest instance is created and pushed to the stack. Once this is done all calls to "Test2::API::context" will find the new hub and send all events to it. When the subtest tool is complete it will remove the new hub, and send a final subtest event to the parent hub.

testing your test tools
    Test2::API::intercept() is implemented using the hub stack. The Test2::API::intercept() function will add an Test2::Hub::Interceptor instance to the stack, any calls to Test2::API::context() will find the new hub, and send it all events. The intercept hub is special in that is has no connection to the parent hub, and usually does not have a formatter.

WHEN SHOULD I ADD A HUB TO THE STACK?
Any time you want to intercept or block events from effecting the test state. Adding a new hub is essentially a way to create a sandbox where you have absolute control over what events do. Adding a new hub insures that the main test state will not be effected.

WHERE IS THE STACK?
The stack is an instance of Test2::API::Stack. You can access the global hub stack using "Test2::API::test2_stack".

WHAT ABOUT THE ROOT HUB?
The root hub is created automatically as needed. A call to "Test2::API::test2_stack->top()" will create the root hub if it does not already exist.

HOW DO HUBS HANDLE IPC?
If the IPC system (Test2::IPC) was not loaded, then IPC is not handled at all. Forking or creating new threads without the IPC system can cause unexpected problems.

All hubs track the PID and Thread ID that was current when they were created. If an event is sent to a hub in a new process/thread the hub will detect this and try to forward the event along to the correct process/thread. This is accomplished using the IPC system.

SEE ALSO
Test2::Manual - Primary index of the manual.

SOURCE
The source code repository for Test2-Manual can be found at https://github.com/Test-More/Test2-Suite/.

MAINTAINERS

Chad Granum <exodist@cpan.org>

AUTHORS
Chad Granum <exodist@cpan.org>

COPYRIGHT
Copyright 2018 Chad Granum <exodist@cpan.org>.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://dev.perl.org/licenses/