Abstract: The invention relates to optimizing software code execution during state transitions. The system handles changes in execution context using differential rule checking techniques. For instance, when a thread executing in a data processing system changes state, its new state may be subject to different rules than its previous state. To enforce these rules, the thread may be associated with software code that causes certain restrictions, such as memory restrictions, to be applied to the thread. In an interpretive environment, this can be implemented by detecting a state transition in an active thread, and responding to the state transition by associating the thread with a dispatch table that reflects its state change. The dispatch table may cause the thread to be associated with code that enforces those restrictions. In one example, different dispatch tables can be provided, each table reflecting a different state of a thread, and each causing a thread to be subject to different restrictions.

Abstract: A technique for implementing a data processor to determine if an exception has been thrown. Specifically, the technique may be used in an interpretive environment where a table known as a bytecode (upcode) dispatch table is used. The dispatch table contains addresses for code that implements each bytecode. When the interpreter executes normally, these addresses point to the basic target machine code for executing each bytecode. However, when an Asynchrounously Interrupted Exception (AIE) is thrown, then the dispatch table is repopulated so that all byte codes point to routines that can handle the exception. These may point to a routine, such as an athrow, that has been extended to handle the special case of the AIE. Alternatively, the rewritten table can point to a routine that is specifically written to handle the firing of an AIE. The table contents are restored to their prior state once the exception handling is complete.