In MobileMedia, most of such exceptions were handled in the core (VC) or by other features (VV or VaVb).
An interesting finding was that even in BerkeleyDB, where most of the exceptions were handled by generic handlers (see Figure 6), the exceptions signaled and handled in the context of a single feature were caught by specific handlers.
Considering the way the exceptions were handled (i.e., by generic or specialized handlers) – regardless of whether they represent exceptions signaled by variable or core features – we could observe that most of the handlers in MobileMedia are specialized handlers, while in BerkeleyDB and Prevayler, generic handlers caught most of the exceptions.
Table 7 Signaler (core or variable) of unhandled exceptions and exception handled on entry point Occurrences MM BkDb Pvl Core Variable Core Variable Core Variable Unhandled 0 0 0 435 162 62 14 Handled on entry point 0 0 314 126 36 4 Total flows 76 35 1058 464 144 20 Figure 17 Relative data about unhandled exception and exception that are handled on or before entry point.
The exception that should be raised in the selected participants is determined in the throw_exception element (line 4), where the exception class is specified via class attribute and the context where the exception will be handled via the target_context attribute.
Instances of GlobalException carry the information of which participant has raised the exception, the context in which this exception was raised (the signaling context), as well as the context in which the exception should be handled (target context).
In this case, a set of concurrent exceptions is signaled to the guardian, which relies on the resolution tree to find a common exception to be handled.
Usually, an exception must be handled immediately, and then control is returned to thread processing.
The ways in which the previous exception cases were handled provides useful information in determining how to handle the current one.
The name of the context is specified by means of the name attribute, whereas the exceptions attribute lists the exceptions that are handled at that context.
