cachedbdbmap.html

用JAVA编写的,在做实验的时候留下来的,本来想删的,但是传上来,大家分享吧

<a name="463" href="#463">463</a>             }
<a name="464" href="#464">464</a>         } <strong>catch</strong> (DatabaseException e) {
<a name="465" href="#465">465</a>             <em class="comment">// Ignore.</em>
<a name="466" href="#466">466</a>         }
<a name="467" href="#467">467</a>         <strong>return</strong> name;
<a name="468" href="#468">468</a>     }
<a name="469" href="#469">469</a>     
<a name="470" href="#470">470</a>     <em>/**<em>*</em></em>
<a name="471" href="#471">471</a> <em>     * Sync in-memory map entries to backing disk store.</em>
<a name="472" href="#472">472</a> <em>     * When done, the memory map will be cleared and all entries stored</em>
<a name="473" href="#473">473</a> <em>     * on disk.</em>
<a name="474" href="#474">474</a> <em>     */</em>
<a name="475" href="#475">475</a>     <strong>public</strong> <strong>synchronized</strong> <strong>void</strong> sync() {
<a name="476" href="#476">476</a>         String dbName = <strong>null</strong>;
<a name="477" href="#477">477</a>         <em class="comment">// Sync. memory and disk.</em>
<a name="478" href="#478">478</a>         <strong>long</strong> startTime = 0;
<a name="479" href="#479">479</a>         <strong>if</strong> (logger.isLoggable(Level.INFO)) {
<a name="480" href="#480">480</a>             dbName = getDatabaseName();
<a name="481" href="#481">481</a>             startTime = System.currentTimeMillis();
<a name="482" href="#482">482</a>             logger.info(dbName + <span class="string">" start sizes: disk "</span> + <strong>this</strong>.diskMapSize +
<a name="483" href="#483">483</a>                 <span class="string">", mem "</span> + <strong>this</strong>.memMap.size());
<a name="484" href="#484">484</a>         }
<a name="485" href="#485">485</a>         expungeStaleEntries();
<a name="486" href="#486">486</a>         LinkedList&lt;SoftEntry> stale = <strong>new</strong> LinkedList&lt;SoftEntry>(); 
<a name="487" href="#487">487</a>         <strong>for</strong> (Iterator i = <strong>this</strong>.memMap.keySet().iterator(); i.hasNext();) {
<a name="488" href="#488">488</a>             Object key = i.next();
<a name="489" href="#489">489</a>             SoftEntry entry = (SoftEntry) memMap.get(key);
<a name="490" href="#490">490</a>             <strong>if</strong> (entry != <strong>null</strong>) {
<a name="491" href="#491">491</a>                 <em class="comment">// Get &amp; hold so not cleared pre-return.</em>
<a name="492" href="#492">492</a>                 Object value = entry.get();
<a name="493" href="#493">493</a>                 <strong>if</strong> (value != <strong>null</strong>) {
<a name="494" href="#494">494</a>                     <strong>this</strong>.diskMap.put(key, value);
<a name="495" href="#495">495</a>                 } <strong>else</strong> {
<a name="496" href="#496">496</a>                     stale.add(entry);
<a name="497" href="#497">497</a>                 }
<a name="498" href="#498">498</a>             }
<a name="499" href="#499">499</a>         }
<a name="500" href="#500">500</a>         <em class="comment">// for any entries above that had been cleared, ensure expunged</em>
<a name="501" href="#501">501</a>         <strong>for</strong> (SoftEntry entry : stale) {
<a name="502" href="#502">502</a>             expungeStaleEntry(entry);
<a name="503" href="#503">503</a>         }   
<a name="504" href="#504">504</a>         
<a name="505" href="#505">505</a>         <strong>if</strong> (logger.isLoggable(Level.INFO)) {
<a name="506" href="#506">506</a>             logger.info(dbName + <span class="string">" sync took "</span> +
<a name="507" href="#507">507</a>                 (System.currentTimeMillis() - startTime) + <span class="string">"ms. "</span> +
<a name="508" href="#508">508</a>                 <span class="string">"Finish sizes: disk "</span> +
<a name="509" href="#509">509</a>                 <strong>this</strong>.diskMapSize + <span class="string">", mem "</span> + <strong>this</strong>.memMap.size());
<a name="510" href="#510">510</a>         }
<a name="511" href="#511">511</a>     }
<a name="512" href="#512">512</a> 
<a name="513" href="#513">513</a>     <strong>private</strong> <strong>void</strong> expungeStaleEntries() {
<a name="514" href="#514">514</a>         <strong>int</strong> c = 0;
<a name="515" href="#515">515</a>         <strong>for</strong>(SoftEntry entry; (entry = (SoftEntry)refQueue.poll()) != <strong>null</strong>;) {
<a name="516" href="#516">516</a>             expungeStaleEntry(entry);
<a name="517" href="#517">517</a>             c++;
<a name="518" href="#518">518</a>         }
<a name="519" href="#519">519</a>         <strong>if</strong> (c > 0 &amp;&amp; logger.isLoggable(Level.FINER)) {
<a name="520" href="#520">520</a>             <strong>try</strong> {
<a name="521" href="#521">521</a>                 logger.finer(<span class="string">"DB: "</span> + db.getDatabaseName() + <span class="string">",  Expunged: "</span>
<a name="522" href="#522">522</a>                         + c + <span class="string">", Diskmap size: "</span> + diskMapSize
<a name="523" href="#523">523</a>                         + <span class="string">", Cache size: "</span> + memMap.size());
<a name="524" href="#524">524</a>             } <strong>catch</strong> (DatabaseException e) {
<a name="525" href="#525">525</a>                 <em class="comment">// Just for logging so ignore Exceptions</em>
<a name="526" href="#526">526</a>             }
<a name="527" href="#527">527</a>         }
<a name="528" href="#528">528</a>     }
<a name="529" href="#529">529</a>     
<a name="530" href="#530">530</a>     <strong>private</strong> <strong>void</strong> expungeStaleEntry(SoftEntry entry) {
<a name="531" href="#531">531</a>         <em class="comment">// If phantom already null, its already expunged -- probably</em>
<a name="532" href="#532">532</a>         <em class="comment">// because it was purged directly first from inside in</em>
<a name="533" href="#533">533</a>         <em class="comment">// {@link #get(String)} and then it went on the poll queue and</em>
<a name="534" href="#534">534</a>         <em class="comment">// when it came off inside in expungeStaleEntries, this method</em>
<a name="535" href="#535">535</a>         <em class="comment">// was called again.</em>
<a name="536" href="#536">536</a>         <strong>if</strong> (entry.getPhantom() == <strong>null</strong>) {
<a name="537" href="#537">537</a>             <strong>return</strong>;
<a name="538" href="#538">538</a>         }
<a name="539" href="#539">539</a>         <em class="comment">// If the object that is in memMap is not the one passed here, then</em>
<a name="540" href="#540">540</a>         <em class="comment">// memMap has been changed -- probably by a put on top of this entry.</em>
<a name="541" href="#541">541</a>         <strong>if</strong> (memMap.get(entry.getPhantom().getKey()) == entry) {
<a name="542" href="#542">542</a>             memMap.remove(entry.getPhantom().getKey());
<a name="543" href="#543">543</a>             diskMap.put(entry.getPhantom().getKey(),
<a name="544" href="#544">544</a>                 entry.getPhantom().doctoredGet());
<a name="545" href="#545">545</a>         }
<a name="546" href="#546">546</a>         entry.clearPhantom();
<a name="547" href="#547">547</a>     }
<a name="548" href="#548">548</a>     
<a name="549" href="#549">549</a>     <strong>private</strong> <strong>class</strong> PhantomEntry <strong>extends</strong> PhantomReference {
<a name="550" href="#550">550</a>         <strong>private</strong> <strong>final</strong> Object key;
<a name="551" href="#551">551</a> 
<a name="552" href="#552">552</a>         <strong>public</strong> PhantomEntry(Object key, Object referent) {
<a name="553" href="#553">553</a>             <strong>super</strong>(referent, <strong>null</strong>);
<a name="554" href="#554">554</a>             <strong>this</strong>.key = key;
<a name="555" href="#555">555</a>         }
<a name="556" href="#556">556</a> 
<a name="557" href="#557">557</a>         <em>/**<em>*</em></em>
<a name="558" href="#558">558</a> <em>         * @return Return the referent. The contract for {@link #get()}</em>
<a name="559" href="#559">559</a> <em>         * always returns a null referent.  We've cheated and doctored</em>
<a name="560" href="#560">560</a> <em>         * PhantomReference to return the actual referent value.  See notes</em>
<a name="561" href="#561">561</a> <em>         * at {@link #referentField};</em>
<a name="562" href="#562">562</a> <em>         */</em>
<a name="563" href="#563">563</a>         <strong>public</strong> Object doctoredGet() {
<a name="564" href="#564">564</a>             <strong>try</strong> {
<a name="565" href="#565">565</a>                 <em class="comment">// Here we use the referentField saved off on static</em>
<a name="566" href="#566">566</a>                 <em class="comment">// initialization of this class to get at this References'</em>
<a name="567" href="#567">567</a>                 <em class="comment">// private referent field.</em>
<a name="568" href="#568">568</a>                 <strong>return</strong> referentField.get(<strong>this</strong>);
<a name="569" href="#569">569</a>             } <strong>catch</strong> (IllegalAccessException e) {
<a name="570" href="#570">570</a>                 <strong>throw</strong> <strong>new</strong> RuntimeException(e);
<a name="571" href="#571">571</a>             }
<a name="572" href="#572">572</a>         }
<a name="573" href="#573">573</a> 
<a name="574" href="#574">574</a>         <em>/**<em>*</em></em>
<a name="575" href="#575">575</a> <em>         * @return Returns the key.</em>
<a name="576" href="#576">576</a> <em>         */</em>
<a name="577" href="#577">577</a>         <strong>public</strong> Object getKey() {
<a name="578" href="#578">578</a>             <strong>return</strong> <strong>this</strong>.key;
<a name="579" href="#579">579</a>         }
<a name="580" href="#580">580</a>     }
<a name="581" href="#581">581</a> 
<a name="582" href="#582">582</a>     <strong>private</strong> <strong>class</strong> SoftEntry <strong>extends</strong> SoftReference {
<a name="583" href="#583">583</a>         <strong>private</strong> PhantomEntry phantom;
<a name="584" href="#584">584</a> 
<a name="585" href="#585">585</a>         <strong>public</strong> SoftEntry(Object key, Object referent, ReferenceQueue q) {
<a name="586" href="#586">586</a>             <strong>super</strong>(referent, q);
<a name="587" href="#587">587</a>             <strong>this</strong>.phantom = <strong>new</strong> PhantomEntry(key, referent);
<a name="588" href="#588">588</a>         }
<a name="589" href="#589">589</a> 
<a name="590" href="#590">590</a>         <em>/**<em>*</em></em>
<a name="591" href="#591">591</a> <em>         * @return Returns the phantom reference.</em>
<a name="592" href="#592">592</a> <em>         */</em>
<a name="593" href="#593">593</a>         <strong>public</strong> PhantomEntry getPhantom() {
<a name="594" href="#594">594</a>             <strong>return</strong> <strong>this</strong>.phantom;
<a name="595" href="#595">595</a>         }
<a name="596" href="#596">596</a>         
<a name="597" href="#597">597</a>         <strong>public</strong> <strong>void</strong> clearPhantom() {
<a name="598" href="#598">598</a>             <strong>this</strong>.phantom.clear();
<a name="599" href="#599">599</a>             <strong>this</strong>.phantom = <strong>null</strong>;
<a name="600" href="#600">600</a>             <strong>super</strong>.clear();
<a name="601" href="#601">601</a>         }
<a name="602" href="#602">602</a>     }
<a name="603" href="#603">603</a>     
<a name="604" href="#604">604</a>     <strong>private</strong> <strong>void</strong> readObject(java.io.ObjectInputStream stream)
<a name="605" href="#605">605</a>     throws IOException, ClassNotFoundException {
<a name="606" href="#606">606</a>         stream.defaultReadObject();
<a name="607" href="#607">607</a>         initializeInstance();
<a name="608" href="#608">608</a>         <strong>if</strong> (logger.isLoggable(Level.FINE)) {
<a name="609" href="#609">609</a>             logger.fine(getDatabaseName() + <span class="string">" diskMapSize: "</span> + diskMapSize);
<a name="610" href="#610">610</a>         }
<a name="611" href="#611">611</a>     }
<a name="612" href="#612">612</a> }
</pre>
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