Mercurial > hg > blitz_stable

annotate src/org/dancres/blitz/entry/OpInfo.java @ 0:3dc0c5604566

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Initial checkin of blitz 2.0 fcs - no installer yet.
author Dan Creswell <dan.creswell@gmail.com>
date Sat, 21 Mar 2009 11:00:06 +0000
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3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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1 package org.dancres.blitz.entry;
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2
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3 import java.io.Serializable;
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4 import java.io.IOException;
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5
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6 import org.dancres.blitz.txn.TxnState;
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7
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8 import org.dancres.blitz.oid.OID;
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9
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10 import org.dancres.blitz.mangler.MangledEntry;
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11
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12 /**
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13 Every operation performed on the disk layer results in an OpInfo being
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14 returned which will contain details of that operation which can be:
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15
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16 <OL>
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17 <LI> Logged to disk for recovery purposes either individually or as part
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18 of a transaction record. In these cases, one recovers the OpInfo and
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19 invokes <code>restore</code> followed by either <code>commit</code> or
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20 <code>abort</code>. </LI>.
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21 <LI> Used to finalize an operation either immediately in the case of a
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22 null transaction or later as part of a full external transaction </LI>
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23 </OL>
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24
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25 Basic interaction with write is to invoke on the WriteBuddy just before
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26 we place the EntrySleeve in the cache so it can set a write lock. We
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27 then return the OpInfo which may be put into the list of a transactions
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28 operations or we commit it and then release the transaction lock asserted
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29 by the WriteBuddy for null transactions <P>
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30
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31 Basic interaction for a read or take is to iterate through EntrySleeves
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32 pinning, offering to buddy and un-pinning. On success from buddy (we
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33 keep a pin applied) knowing a transaction lock has been asserted. We then
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34 return the OpInfo which will, again, either be commited immediately or
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35 stored for a later commit. <P>
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36
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37 Note that, because underlying implementations always pin their respective
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38 entries in a cache, the Entry will be in cache and will be updated in
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39 cache (because it can't be flushed). This means that restore can throw
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40 a IOException as it reloads state but neither of commit or abort can.
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41 */
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42 public interface OpInfo extends Serializable {
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43
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44 /**
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45 @return <code>true</code> if this operation is a debug operation with
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46 no state that needs preserving
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47 */
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48 public boolean isDebugOp();
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49
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50 /**
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51 Restore memory-state required to apply this OpInfo.
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52 */
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53 public void restore() throws IOException;
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54
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55 /**
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56 Apply the action implied by this OpInfo to the underlying FS.
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57
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58 @return the entry associated with the UID of this OpInfo if it
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59 still exists (is not deleted).
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60 */
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61 public MangledEntry commit(TxnState aState) throws IOException;
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62
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63 /**
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64 Abort the action implied by this OpInfo to the underlying FS.
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65
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66 @return the entry associated with the UID of this OpInfo if it
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67 still exists (is not deleted).
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68 */
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69 public MangledEntry abort(TxnState aState) throws IOException;
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70
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71 public String getType();
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72
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73 public OID getOID();
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74 }