[xwiki-devs] [VOTE] Property declarations for the execution context

Hi Everyone, I would like you to vote on merging the feature-execution-context branches of commons and platform before the release of 4.3M2: https://github.com/xwiki/xwiki-commons/compare/master...feature-execution-c… https://github.com/xwiki/xwiki-platform/compare/master...feature-execution-… Explanation of the feature: The execution context is a simple map that binds a string to an object. This can be compared to how variables are handled by scripting languages such as bash, where an assignment brings the variable into existance: $ my_variable="some value" In the case of the execution context, the syntax is: context.setProperty("my_variable", "some value"); This feature is about adding property declarations, where a property can be associated with attributes that controls how the execution context and execution context manager handles the property. The general idea can, once again, be compared to bash and how it is possible to declare variables there: $ declare -ru my_variable="read only, forced upper case" Of course, the set of attributes that are interesting to us is different from bash. Currently the feature branch have support for declaring properties with these attributes: * Final - The value may not be updated within the the execution context. Default: false. * Inherited - The property will be inherited from the current context when replacing the execution context within the current scope. Default: false. * Cloned value - Also clone the value when the execution context is cloned. Default: false. * Type - The class of the value, for typechecking when setting the value. Default: null (unchecked). * Non-null - The value may not be null, checked when setting the value. Default: false. Example declaration: ExecutionContextProperty property = new ExecutionContextProperty("my_variable"); property.setValue("some value"); property.setType(String.class); property.setInherited(true); context.declareProperty(property); The property value may be updated and the property may be removed and redeclared, unless declared 'final': context.setProperty("my_variable", "some new value"); context.removeProperty("my_variable"); Additional attributes may be added later. This feature is also backwards compliant, in that implicit declaration by just setting a value is allowed. (Although we might want to make explicit declarations mandatory in the future.) Within the scope of a request, or the life time of a thread executing some administrative task (e.g., the lucene index updater) the basic life cycle of the execution context is the following: @Inject Execution execution; @Inject ExecutionContextManager ecm; ExecutionContext context = new ExecutionContext(); ecm.initialize(context); try { // Do work } finally { ecm.removeContext(); } Within the life cycle of the "root" execution context, we may push a new execution context, which may either be a clean context, or a clone of the current context: // Pushing a clone ExecutionContext context = ecm.clone(execution.getContext()); execution.pushContext(context); try { // Do work } finally { execution.popContext(); } // Pushing a clean context ExecutionContext context = new ExecutionContext(); execution.pushContext(context); try { // Do work } finally { execution.popContext(); } Component authors that needs to place a value in the execution context provides an initializer that declares the variable and sets an initial value. The attributes 'final', 'cloned value', and 'inherited' lets component authors control how the value is managed during the lifecycle of the root execution context. The attributes 'type' and 'non-null' provides some runtime assertions to catch some errors earlier. So to summarize, this feature: 1. is a convenient mechanism for managing properties in the execution context, 2. provides some validation of the property values, 3. improves performance slightly by avoiding unnecessary cloning. For more information, see the proposal thread: http://xwiki.475771.n2.nabble.com/PROPOSAL-Execution-context-property-decla… Best Regards, /Andreas