Valid phase order configurations may result in invalid phase execution orders
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Key: AXIS2-5267
URL: https://issues.apache.org/jira/browse/AXIS2-5267
Project: Axis2
Issue Type: Bug
Components: kernel
Affects Versions: 1.5.4
Reporter: James Grahn
The partial ordering of Axis2 handlers is not fully enforced.
Given a case with two handlers that ought to be run before a third, the system
may fail as implemented.
The current ordering system permits a configuration which is valid by
inspection yet fails to enforce the described order. This property of the
system emerges from both the configuration and the time at which phase ordering
is checked.
If my system relies on both A and B coming before C, I cannot state this
dependency directly (see AXIS2-5266). However, I can invert this dependency
and say A and B require C to follow.
Because phase rules are only checked at insertion time, if A and B are inserted
first, they are merely shifted to the beginning of the phase list (C is not yet
present). The resultant phase list after the insertion of A and B might be:
(B,A,X,Y,Z).
If C specifies that B comes before it in its rule (which is a valid, albeit
incomplete requirement), then C might be inserted immediately after B,
resulting in this invalid phase ordering: (B,C,A,X,Y,Z).
This example of valid configuration yielding invalid phase ordering constitutes
a defect in the configuration.
This defect could resolved by allowing the specification of multiple "before"
and "after" handlers (see AXIS2-5266), creating a dependency graph, and
resolving a valid ordering from the graph. A dependency graph may also
generalize many of the validation steps currently performed into a cycle
detection step. (Even phasefirst and phaselast rules amount to cycle
detection if they are properly represented in the graph.) A dependency graph
would also allow for confirmation that all dependencies are in place before a
service is started.
I believe this change would make the system more robust, and because the
dependencies would be resolved in a linear chain at service startup, there's no
ongoing performance penalty for creating/maintaining a more complex data
structure.
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