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POmultiple threads using same value fetched by database DAO class method
 

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  1. POmultiple threads using same value fetched by database DAO class method
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    <p><strong><code>Status: solved</code></strong></p> <p>I had to make a pastebin as I had to point out line numbers.</p> <p><strong>note:</strong> not using executorsService or thread pools. just to understand that what is wrong in starting and using threads this way. <strong>If I use 1 thread. the app works Perfect!</strong></p> <p>related links:</p> <p><a href="http://www.postgresql.org/docs/9.1/static/transaction-iso.html" rel="nofollow">http://www.postgresql.org/docs/9.1/static/transaction-iso.html</a> <a href="http://www.postgresql.org/docs/current/static/explicit-locking.html" rel="nofollow">http://www.postgresql.org/docs/current/static/explicit-locking.html</a></p> <p><code>main app,</code> <a href="http://pastebin.com/i9rVyari" rel="nofollow">http://pastebin.com/i9rVyari</a> <code>logs</code>, <a href="http://pastebin.com/2c4pU1K8" rel="nofollow">http://pastebin.com/2c4pU1K8</a> , <a href="http://pastebin.com/2S3301gD" rel="nofollow">http://pastebin.com/2S3301gD</a></p> <p>I am starting many threads (10) in a for loop with instantiating a <code>runnable</code> class but it seems I am getting same result from <code>db</code> (I am geting some string from db, then changing it) but with <strong><code>each thread, I get same string</code></strong> (despite each thread changed it.) . using <code>jdbc</code> for <code>postgresql</code> what might be the usual issues ?</p> <pre><code>line 252 and line 223 </code></pre> <p>the link is marked as <code>processed. (true)</code> in db. other threads of <code>crawler class</code> also do it. so when <code>line 252</code> should get a link. it should be <code>processed = false</code>. but I see all <code>threads take same link.</code></p> <p>when one of the threads crawled the link . it makes it processed = true. the others then should not crawl it. (get it) is its marked processed = true. </p> <hr> <p><code>getNonProcessedLinkFromDB()</code> returns a non processed link</p> <pre><code>public String getNonProcessedLink(){ line 645 public boolean markLinkAsProcesed(String link){ line 705 </code></pre> <p><code>getNonProcessedLinkFromDB</code> will see for processed = false links and give one out of them . <code>limit 1</code> <strong>each thread has a starting interval gap of 20 secs.</strong><br> within one thread. 1 or 2 seconds (estimate processing time for crawling)</p> <pre><code>line 98 keepS threads from grabbing the same url </code></pre> <p><strong>if you see the result. one thread made it true. still others access it. waaaay after some time.</strong></p> <p>all thread are seperate. even one <code>races</code>. the <strong>db makes the link true at the moment the first thread processes it</strong></p>
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    1. USMasood Ahmad
    1. USMasood Ahmad
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    1. COAre you re-using the same database connection?
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      1. POmultiple threads using same value fetched by database DAO class method
      1. USGray
    2. COI use `new BasicDao().method();` I have tried to make those methods as `static` too. or put their call in a `sycnhronized block` or make the `boolean` that they return as `volatile` . but no use.
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      1. POmultiple threads using same value fetched by database DAO class method
      1. USMasood Ahmad
 

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