--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/dancres/blitz/entry/OpInfo.java	Sat Mar 21 11:00:06 2009 +0000
@@ -0,0 +1,74 @@
+package org.dancres.blitz.entry;
+
+import java.io.Serializable;
+import java.io.IOException;
+
+import org.dancres.blitz.txn.TxnState;
+
+import org.dancres.blitz.oid.OID;
+
+import org.dancres.blitz.mangler.MangledEntry;
+
+/**
+   Every operation performed on the disk layer results in an OpInfo being
+   returned which will contain details of that operation which can be:
+
+   <OL>
+   <LI> Logged to disk for recovery purposes either individually or as part
+   of a transaction record.  In these cases, one recovers the OpInfo and
+   invokes <code>restore</code> followed by either <code>commit</code> or
+   <code>abort</code>. </LI>.
+   <LI> Used to finalize an operation either immediately in the case of a
+   null transaction or later as part of a full external transaction </LI>
+   </OL>
+
+   Basic interaction with write is to invoke on the WriteBuddy just before
+   we place the EntrySleeve in the cache so it can set a write lock.  We
+   then return the OpInfo which may be put into the list of a transactions
+   operations or we commit it and then release the transaction lock asserted
+   by the WriteBuddy for null transactions <P>
+
+   Basic interaction for a read or take is to iterate through EntrySleeves
+   pinning, offering to buddy and un-pinning.  On success from buddy (we
+   keep a pin applied) knowing a transaction lock has been asserted.  We then
+   return the OpInfo which will, again, either be commited immediately or
+   stored for a later commit. <P>
+
+   Note that, because underlying implementations always pin their respective
+   entries in a cache, the Entry will be in cache and will be updated in
+   cache (because it can't be flushed).  This means that restore can throw
+   a IOException as it reloads state but neither of commit or abort can.
+*/
+public interface OpInfo extends Serializable {
+
+    /**
+       @return <code>true</code> if this operation is a debug operation with
+       no state that needs preserving
+     */
+    public boolean isDebugOp();
+
+    /**
+       Restore memory-state required to apply this OpInfo.
+     */
+    public void restore() throws IOException;
+
+    /**
+       Apply the action implied by this OpInfo to the underlying FS.
+       
+       @return the entry associated with the UID of this OpInfo if it
+       still exists (is not deleted).
+     */
+    public MangledEntry commit(TxnState aState) throws IOException;
+
+    /**
+       Abort the action implied by this OpInfo to the underlying FS.
+       
+       @return the entry associated with the UID of this OpInfo if it
+       still exists (is not deleted).
+     */
+    public MangledEntry abort(TxnState aState) throws IOException;
+
+    public String getType();
+
+    public OID getOID();
+}