bdbmultipleworkqueues.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="278" href="#278">278</a>     
<a name="279" href="#279">279</a>     <strong>protected</strong> OperationStatus getNextNearestItem(DatabaseEntry headKey,
<a name="280" href="#280">280</a>             DatabaseEntry result) throws DatabaseException {
<a name="281" href="#281">281</a>         Cursor cursor = <strong>null</strong>;
<a name="282" href="#282">282</a>         OperationStatus status;
<a name="283" href="#283">283</a>         <strong>try</strong> {
<a name="284" href="#284">284</a>             cursor = <strong>this</strong>.pendingUrisDB.openCursor(<strong>null</strong>, <strong>null</strong>);
<a name="285" href="#285">285</a>             <em class="comment">// get cap; headKey at this point should always point to </em>
<a name="286" href="#286">286</a>             <em class="comment">// a queue-beginning cap entry (zero-length value)</em>
<a name="287" href="#287">287</a>             status = cursor.getSearchKey(headKey, result, <strong>null</strong>);
<a name="288" href="#288">288</a>             <strong>if</strong>(status!=OperationStatus.SUCCESS || result.getData().length > 0) {
<a name="289" href="#289">289</a>                 <em class="comment">// cap missing</em>
<a name="290" href="#290">290</a>                 <strong>throw</strong> <strong>new</strong> DatabaseException(<span class="string">"bdb queue cap missing"</span>);
<a name="291" href="#291">291</a>             }
<a name="292" href="#292">292</a>             <em class="comment">// get next item (real first item of queue)</em>
<a name="293" href="#293">293</a>             status = cursor.getNext(headKey,result,<strong>null</strong>);
<a name="294" href="#294">294</a>         } <strong>finally</strong> { 
<a name="295" href="#295">295</a>             <strong>if</strong>(cursor!=<strong>null</strong>) {
<a name="296" href="#296">296</a>                 cursor.close();
<a name="297" href="#297">297</a>             }
<a name="298" href="#298">298</a>         }
<a name="299" href="#299">299</a>         <strong>return</strong> status;
<a name="300" href="#300">300</a>     }
<a name="301" href="#301">301</a>     
<a name="302" href="#302">302</a>     <em>/**<em>*</em></em>
<a name="303" href="#303">303</a> <em>     * Put the given CrawlURI in at the appropriate place. </em>
<a name="304" href="#304">304</a> <em>     * </em>
<a name="305" href="#305">305</a> <em>     * @param curi</em>
<a name="306" href="#306">306</a> <em>     * @throws DatabaseException</em>
<a name="307" href="#307">307</a> <em>     */</em>
<a name="308" href="#308">308</a>     <strong>public</strong> <strong>void</strong> put(<a href="../../../../org/archive/crawler/datamodel/CrawlURI.html">CrawlURI</a> curi) throws DatabaseException {
<a name="309" href="#309">309</a>         DatabaseEntry insertKey = (DatabaseEntry)curi.getHolderKey();
<a name="310" href="#310">310</a>         <strong>if</strong> (insertKey == <strong>null</strong>) {
<a name="311" href="#311">311</a>             insertKey = calculateInsertKey(curi);
<a name="312" href="#312">312</a>             curi.setHolderKey(insertKey);
<a name="313" href="#313">313</a>         }
<a name="314" href="#314">314</a>         DatabaseEntry value = <strong>new</strong> DatabaseEntry();
<a name="315" href="#315">315</a>         crawlUriBinding.objectToEntry(curi, value);
<a name="316" href="#316">316</a>         <em class="comment">// Output tally on avg. size if level is FINE or greater.</em>
<a name="317" href="#317">317</a>         <strong>if</strong> (LOGGER.isLoggable(Level.FINE)) {
<a name="318" href="#318">318</a>             tallyAverageEntrySize(curi, value);
<a name="319" href="#319">319</a>         }
<a name="320" href="#320">320</a>         pendingUrisDB.put(<strong>null</strong>, insertKey, value);
<a name="321" href="#321">321</a>     }
<a name="322" href="#322">322</a>     
<a name="323" href="#323">323</a>     <strong>private</strong> <strong>long</strong> entryCount = 0;
<a name="324" href="#324">324</a>     <strong>private</strong> <strong>long</strong> entrySizeSum = 0;
<a name="325" href="#325">325</a>     <strong>private</strong> <strong>int</strong> largestEntry = 0;
<a name="326" href="#326">326</a>     
<a name="327" href="#327">327</a>     <em>/**<em>*</em></em>
<a name="328" href="#328">328</a> <em>     * Log average size of database entry.</em>
<a name="329" href="#329">329</a> <em>     * @param curi CrawlURI this entry is for.</em>
<a name="330" href="#330">330</a> <em>     * @param value Database entry value.</em>
<a name="331" href="#331">331</a> <em>     */</em>
<a name="332" href="#332">332</a>     <strong>private</strong> <strong>synchronized</strong> <strong>void</strong> tallyAverageEntrySize(<a href="../../../../org/archive/crawler/datamodel/CrawlURI.html">CrawlURI</a> curi,
<a name="333" href="#333">333</a>             DatabaseEntry value) {
<a name="334" href="#334">334</a>         entryCount++;
<a name="335" href="#335">335</a>         <strong>int</strong> length = value.getData().length;
<a name="336" href="#336">336</a>         entrySizeSum += length;
<a name="337" href="#337">337</a>         <strong>int</strong> avg = (<strong>int</strong>) (entrySizeSum/entryCount);
<a name="338" href="#338">338</a>         <strong>if</strong>(entryCount % 1000 == 0) {
<a name="339" href="#339">339</a>             LOGGER.fine(<span class="string">"Average entry size at "</span>+entryCount+<span class="string">": "</span>+avg);
<a name="340" href="#340">340</a>         }
<a name="341" href="#341">341</a>         <strong>if</strong> (length>largestEntry) {
<a name="342" href="#342">342</a>             largestEntry = length; 
<a name="343" href="#343">343</a>             LOGGER.fine(<span class="string">"Largest entry: "</span>+length+<span class="string">" "</span>+curi);
<a name="344" href="#344">344</a>             <strong>if</strong>(length>(2*avg)) {
<a name="345" href="#345">345</a>                 LOGGER.fine(<span class="string">"excessive?"</span>);
<a name="346" href="#346">346</a>             }
<a name="347" href="#347">347</a>         }
<a name="348" href="#348">348</a>     }
<a name="349" href="#349">349</a> 
<a name="350" href="#350">350</a>     <em>/**<em>*</em></em>
<a name="351" href="#351">351</a> <em>     * Calculate the 'origin' key for a virtual queue of items</em>
<a name="352" href="#352">352</a> <em>     * with the given classKey. This origin key will be a </em>
<a name="353" href="#353">353</a> <em>     * prefix of the keys for all items in the queue. </em>
<a name="354" href="#354">354</a> <em>     * </em>
<a name="355" href="#355">355</a> <em>     * @param classKey String key to derive origin byte key from </em>
<a name="356" href="#356">356</a> <em>     * @return a byte array key </em>
<a name="357" href="#357">357</a> <em>     */</em>
<a name="358" href="#358">358</a>     <strong>static</strong> byte[] calculateOriginKey(String classKey) {
<a name="359" href="#359">359</a>         byte[] classKeyBytes = <strong>null</strong>;
<a name="360" href="#360">360</a>         <strong>int</strong> len = 0;
<a name="361" href="#361">361</a>         <strong>try</strong> {
<a name="362" href="#362">362</a>             classKeyBytes = classKey.getBytes(<span class="string">"UTF-8"</span>);
<a name="363" href="#363">363</a>             len = classKeyBytes.length;
<a name="364" href="#364">364</a>         } <strong>catch</strong> (UnsupportedEncodingException e) {
<a name="365" href="#365">365</a>             <em class="comment">// should be impossible; all JVMs must support UTF-8</em>
<a name="366" href="#366">366</a>             e.printStackTrace();
<a name="367" href="#367">367</a>         }
<a name="368" href="#368">368</a>         byte[] keyData = <strong>new</strong> byte[len+1];
<a name="369" href="#369">369</a>         System.arraycopy(classKeyBytes,0,keyData,0,len);
<a name="370" href="#370">370</a>         keyData[len]=0;
<a name="371" href="#371">371</a>         <strong>return</strong> keyData;
<a name="372" href="#372">372</a>     }
<a name="373" href="#373">373</a>     
<a name="374" href="#374">374</a>     <em>/**<em>*</em></em>
<a name="375" href="#375">375</a> <em>     * Calculate the insertKey that places a CrawlURI in the</em>
<a name="376" href="#376">376</a> <em>     * desired spot. First bytes are always classKey (usu. host)</em>
<a name="377" href="#377">377</a> <em>     * based -- ensuring grouping by host -- terminated by a zero</em>
<a name="378" href="#378">378</a> <em>     * byte. Then 8 bytes of data ensuring desired ordering </em>
<a name="379" href="#379">379</a> <em>     * within that 'queue' are used. The first byte of these 8 is</em>
<a name="380" href="#380">380</a> <em>     * priority -- allowing 'immediate' and 'soon' items to </em>
<a name="381" href="#381">381</a> <em>     * sort above regular. Next 1 byte is 'cost'. Last 6 bytes </em>
<a name="382" href="#382">382</a> <em>     * are ordinal serial number, ensuring earlier-discovered </em>
<a name="383" href="#383">383</a> <em>     * URIs sort before later. </em>
<a name="384" href="#384">384</a> <em>     * </em>
<a name="385" href="#385">385</a> <em>     * NOTE: Dangers here are:</em>
<a name="386" href="#386">386</a> <em>     * (1) priorities or costs over 2^7 (signed byte comparison)</em>
<a name="387" href="#387">387</a> <em>     * (2) ordinals over 2^48</em>
<a name="388" href="#388">388</a> <em>     * </em>
<a name="389" href="#389">389</a> <em>     * Package access &amp; static for testing purposes. </em>
<a name="390" href="#390">390</a> <em>     * </em>
<a name="391" href="#391">391</a> <em>     * @param curi</em>
<a name="392" href="#392">392</a> <em>     * @return a DatabaseEntry key for the CrawlURI</em>
<a name="393" href="#393">393</a> <em>     */</em>
<a name="394" href="#394">394</a>     <strong>static</strong> DatabaseEntry calculateInsertKey(<a href="../../../../org/archive/crawler/datamodel/CrawlURI.html">CrawlURI</a> curi) {
<a name="395" href="#395">395</a>         byte[] classKeyBytes = <strong>null</strong>;
<a name="396" href="#396">396</a>         <strong>int</strong> len = 0;
<a name="397" href="#397">397</a>         <strong>try</strong> {
<a name="398" href="#398">398</a>             classKeyBytes = curi.getClassKey().getBytes(<span class="string">"UTF-8"</span>);
<a name="399" href="#399">399</a>             len = classKeyBytes.length;
<a name="400" href="#400">400</a>         } <strong>catch</strong> (UnsupportedEncodingException e) {
<a name="401" href="#401">401</a>             <em class="comment">// should be impossible; all JVMs must support UTF-8</em>
<a name="402" href="#402">402</a>             e.printStackTrace();
<a name="403" href="#403">403</a>         }
<a name="404" href="#404">404</a>         byte[] keyData = <strong>new</strong> byte[len+9];
<a name="405" href="#405">405</a>         System.arraycopy(classKeyBytes,0,keyData,0,len);
<a name="406" href="#406">406</a>         keyData[len]=0;
<a name="407" href="#407">407</a>         <strong>long</strong> ordinalPlus = curi.getOrdinal() &amp; 0x0000FFFFFFFFFFFFL;
<a name="408" href="#408">408</a>         ordinalPlus = 
<a name="409" href="#409">409</a>         	((<strong>long</strong>)curi.getSchedulingDirective() &lt;&lt; 56) | ordinalPlus;
<a name="410" href="#410">410</a>         ordinalPlus = 
<a name="411" href="#411">411</a>         	((((<strong>long</strong>)curi.getHolderCost()) &amp; 0xFFL) &lt;&lt; 48) | ordinalPlus;
<a name="412" href="#412">412</a>         ArchiveUtils.longIntoByteArray(ordinalPlus, keyData, len+1);
<a name="413" href="#413">413</a>         <strong>return</strong> <strong>new</strong> DatabaseEntry(keyData);
<a name="414" href="#414">414</a>     }
<a name="415" href="#415">415</a>     
<a name="416" href="#416">416</a>     <em>/**<em>*</em></em>
<a name="417" href="#417">417</a> <em>     * Delete the given CrawlURI from persistent store. Requires</em>
<a name="418" href="#418">418</a> <em>     * the key under which it was stored be available. </em>
<a name="419" href="#419">419</a> <em>     * </em>
<a name="420" href="#420">420</a> <em>     * @param item</em>