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POJava IllegalMonitorStateException on tryLock
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copied!<p>I was wondering if someone could help me. I'm new to concurrent programming and I've got the following code which at times is giving me an IllegalMonitorStateException as a Thread that does not currently own the lock is trying to unlock.</p> <p>I was told on the OTN forum that to prevent this and deadlock from occurring that I should make sure that the lowest indexes are locked first but I can't figure out how to do this. could one of you please point me in the right direction.</p> <p>Many thanks.</p> <pre><code> import java.util.concurrent.locks.*; class ShuffleBase { ReentrantLock [] locker; int [] data; int x; ReentrantLock lock1; ReentrantLock lock2; public ShuffleBase(int [] d){ x=0; data=d; locker = new ReentrantLock[d.length]; while (x!=data.length) { locker[x]=new ReentrantLock(); x++; } } /* * Boolean method to test if both indexes are locked * Returning their status for use in the method swap * If locked the swap happens else the locks are * released */ public boolean lockedIndex(int a, int b){ Boolean lockA = false; Boolean lockB = false; try{ lockA = lock1.tryLock(); lockB = lock2.tryLock(); }finally{ if (!(lockA && lockB)) { if(lockA){ lock1.unlock(); } if (lockB){ lock2.unlock(); } }// end of IF ! lockA & lockB } // End of finally return lockA && lockB; }// End of lockedIndex public void swap(int a, int b){ int temp; lock1 = locker[a]; lock2=locker[b]; //If a & b aren't the same index swap if(a!=b) { if(lockedIndex(a,b)) { try{ temp=data[b]; data[b]=data[a]; data[a]=temp; }finally{ lock1.unlock(); lock2.unlock(); } } else{System.out.println("Couldn't lock");} } else{return;} }//EOF Method public void display(){ System.out.println("The array when swapped"); for(int j=0; j<data.length;j++) { System.out.print(data[j]+", "); } }// End of Display }// EOC </code></pre> <hr> <p>Thank you all for your answers, yes I am doing this as part of a self learning/homework. I've changed the code to the following as I believe that this is what Rodion suggested, I hope I interpreted your suggestion correctly. Mtraut I've also made the changes you suggested and I can't believe that I made these mistakes :-) Thanks for spotting them.</p> <pre><code>import java.util.concurrent.locks.*; class ShuffleBase { ReentrantLock [] locker; int [] data; int x=0; public ShuffleBase(int [] d){ data=d; locker = new ReentrantLock[d.length]; while (x!=data.length) { locker[x]=new ReentrantLock(); x++; } } /* * Boolean method to test if both indexes are locked * Returning their status for use in the method swap * If locked the swap happens else the locks are * released */ private boolean lockedIndex(int a, int b){ Boolean lockA = false; Boolean lockB = false; try{ lockA = locker[a].tryLock(); lockB = locker[b].tryLock(); }finally{ if (!(lockA && lockB)) { if(lockA){ locker[a].unlock(); } if (lockB){ locker[b].unlock(); } }// end of IF ! lockA & lockB } // End of finally return lockA && lockB; }// End of lockedIndex public void swap(int a, int b){ int temp; //If a & b aren't the same index swap if(a!=b) { if(lockedIndex(a,b)) { try{ temp=data[b]; data[b]=data[a]; data[a]=temp; }finally{ locker[a].unlock(); locker[b].unlock(); } } else{System.out.println("Couldn't lock");} } else{System.out.println(return;} }//EOF Method public void display(){ System.out.println("The array when swapped"); for(int j=0; j<data.length;j++) { System.out.print(data[j]+", "); } }// End of Display }// EOC </code></pre> <p>Thanks again for all of your answers and apologies for my late reply.</p>

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