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annotate src/org/dancres/blitz/oid/Allocator.java @ 32:243c74d599bf

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author Dan Creswell <dan.creswell@gmail.com>
date Sat, 12 Jun 2010 10:41:47 +0100
parents 3dc0c5604566
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3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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1 package org.dancres.blitz.oid;
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2
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3 import java.io.IOException;
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4
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5 /**
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6 <p>An Allocator generates a series of UIDImpl's each of which is
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7 guarenteed to be unique within the scope of the Allocator. Note that
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8 allocated id's are not re-used so an Allocator can, potentially, become
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9 exhausted. This can be avoided by allowing the allocator sufficient
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10 space to allocate from by increasing the maximum number of available
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11 allocator ids.</p>
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12
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13 <p>Allocator's are self-recovering. They check <code>BootContext</code>
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14 for the presence of a <code>SyncBarrier</code> instance which indicates
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15 the maximum number of log operations between checkpoints. This number
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16 represents the maximum number of entry writes or notify registrations which
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17 could have been carried out without the appropriate Allocator instances
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18 being sync'd to disk. Thus, the allocator simply ensures that all it's
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19 oid generators are incremented by the value of the SyncBarrier and sync'd
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20 back to disk. This guarentees that there will be no oid overlap and
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21 means that "user code" need not be involved in the recovery process.</p>
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22 */
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23 public interface Allocator {
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24 public OID getNextId() throws IOException;
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25
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26 /**
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27 @return the maximum number of zone id's this Allocator instance
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28 is allowed to use.
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29 */
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30 public int getMaxZoneId();
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31 }