Backtracking for Distributed Model Execution Refactoring Preview Batch Refactoring Actions and Settings Ptolemy Editor Backtracking Motivation – Distributed model execution requires backtracking. When a component receives a message tagged with a time in its past, it must rollback and process the message in the correct sequential order. – Incremental backtracking aims to capture every change in model states. Every time an actor assigns a new value to its private non-static field (state), the old value must be remembered so that a rollback can be issued later. Automatic Java Source Refactoring – It is boring for the programmers to manually capture all the changes, so we take a refactoring approach. – An Eclipse plug-in refactors actor source code as it is being written. A command-line tool is implemented to refactor a list of sources at a time. Backtracking with Checkpoint Objects – A checkpoint object monitors a group of objects to be checkpointed and rolled back at the same time. – A timestamp is the handle of a checkpoint. – The rollback method of a checkpoint object rolls the state back to a previous timestamp. Modified SDF Director – In its original design, SDF does not conform to the prefire-fire-postfire semantics. – The modified SDF director conforms to the prefire-fire-postfire semantics by recording a checkpoint before the first fire. – SDF composite actors can now be embedded in CT and provide the correct semantics in a clean way. prefire create checkpoint firerollback delete checkpoint postfire package mypackage; import java.io.InputStream; /** * A buffer of predefined size for an input stream. */ public class StreamBuffer { /** * Construct a buffer with an input stream. */ public StreamBuffer(InputStream stream) { _stream = stream; } /** * Return the next byte in the buffer. If the buffer * is empty, more bytes are read from the input stream. */ public byte nextByte() throws Exception { if (_pointer >= SIZE) { _stream.read(_buffer); _pointer = 0; } return _buffer[_pointer++]; } /** * Size of the buffer. */ public static final int SIZE = 20; // The buffer. private byte[] _buffer = new byte[SIZE]; // The current read position in the buffer. private int _pointer = SIZE; // The input stream to be read. private InputStream _stream; } package refactored.mypackage; import java.io.InputStream; import java.lang.Object; import ptolemy.backtrack.Checkpoint; import ptolemy.backtrack.Rollbackable; import ptolemy.backtrack.util.CheckpointRecord; import ptolemy.backtrack.util.FieldRecord; /** * A buffer of predefined size for an input stream. */ public class StreamBuffer implements Rollbackable { protected Checkpoint $CHECKPOINT = new Checkpoint(this); /** * Size of the buffer. */ public static final int SIZE = 20; // The buffer. private byte[] _buffer = new byte[SIZE]; // The current read position in the buffer. private int _pointer = SIZE; // The input stream to be read. private InputStream _stream; /** * Construct a buffer with an input stream. */ public StreamBuffer(InputStream stream) { $ASSIGN$_stream(stream); } /** * Return the next byte in the buffer. If the buffer * is empty, more bytes are read from the input stream. */ public byte nextByte() throws Exception { if (_pointer >= SIZE) { _stream.read($BACKUP$_buffer()); $ASSIGN$_pointer(0); } return _buffer[$ASSIGN$SPECIAL$_pointer(11, _pointer)]; } // Extra fields and methods omitted.... }