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POConcurrentModificationException on synchronized method
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  1. POConcurrentModificationException on synchronized method
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    copied!<p>I'm processing a lot of events that come from a TCP socket (sets of ten per second), so I'm using multithreading to process those events.</p> <pre><code>public class MainActivity extends Activity { ... // In this Map I store the tab name and the associated TabHost.TabSpec instance private static Map&lt;String, TabHost.TabSpec&gt; Tabs = Collections.synchronizedMap(new LinkedHashMap&lt;String, TabHost.TabSpec&gt;()); // In this Map I store pairs of tab-names and a HashSet of undelivered messages // It's a class that extends Map&lt;String, HashSet&lt;String&gt;&gt; with some additional functions that doesn't have anything to do with Tabs. private static NamesListing Names = Collections.synchronizedMap(new LinkedHashMap&lt;String, HashSet&lt;String&gt;&gt;()); // Yes, I know the names don't follow the Java standards, but I keeped them for mantaining the question coherence. I will change it in my code, though. synchronized private static void ProcessEvent(final String name, final String message) { // Low-priority thread final Thread lowp = new Thread( new Runnable() { public void run() { final Iterator&lt;String&gt; iter = Tabs.keySet().iterator(); while (iter.hasNext()) { final String tabname = iter.next(); // This just returns an int making some calculations over the tabname final int Status = Names.getUserStatus(tabname, message); // Same than getUserStatus if ((Names.isUserSpecial(Status)) &amp;&amp; (name.equals(tabname))) { // This just removes a line from the HashSet Names.delLine(tabname, message); } } } }); lowp.setPriority(3); lowp.start(); } ... } </code></pre> <p>Most of time this works right, but sometimes there are some avalanches of those events, and somethimes I get a ConcurrentModificationException:</p> <blockquote> <p>12-10 14:08:42.071: E/AndroidRuntime(28135): FATAL EXCEPTION: Thread-369 12-10 14:08:42.071: E/AndroidRuntime(28135): java.util.ConcurrentModificationException 12-10 14:08:42.071: E/AndroidRuntime(28135): at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:347) 12-10 14:08:42.071: E/AndroidRuntime(28135): at java.util.LinkedHashMap$KeyIterator.next(LinkedHashMap.java:367) 12-10 14:08:42.071: E/AndroidRuntime(28135): at es.irchispano.chat.MainActivity$6.run(MainActivity.java:244) 12-10 14:08:42.071: E/AndroidRuntime(28135): at java.lang.Thread.run(Thread.java:841)</p> </blockquote> <p>Note: The 244 line corresponds to the</p> <pre><code>final String tabname = iter.next(); </code></pre> <p>statement.</p> <p>It seems weird to me as I'm using a Collections.synchronizedMap and the method that processes those lines is synchronized, so why is it still happening?</p> <p>Thanks!</p> <p><strong>---------- Edited ----------</strong></p> <p>Sorry for the concise initial code; I've tried to simplify as much as possible but obviously it was not a good idea. I'm pasting the actual code. Of course each of those structures are initialized (otherwise I wouldn't have a problem :-)), now I'm going to read all your comments with conscience and I'll post what I'll find out. Thank you all for the support!</p>
 

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