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POIllegal State Monitor Exception in distributed system
 

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    <p>this is my code. It's supposed to implement a way of synchronizing calls in a distributed system. This is the part where i send the message and wait for acks. The network and the peers are supposed reliable.</p> <p>My problem though is related to local sync, because it keeps raising this exception and i cannot understand why.</p> <pre><code>Exception in thread "Thread-7" java.lang.IllegalMonitorStateException at java.lang.Object.wait(Native Method) at java.lang.Object.wait(Object.java:503) at distributed.PeerManager.sendAllWithAck(PeerManager.java:212) at distributed.TokenManager.onTokenReceived(TokenManager.java:67) at communication.TokenMessage.execute(TokenMessage.java:21) at distributed.ListenThread.run(ListenThread.java:38) Exception in thread "Thread-8" java.lang.IllegalMonitorStateException at java.lang.Object.notify(Native Method) at distributed.AckWaiter.run(AckWaiter.java:74) </code></pre> <p>Here's the AckWaiter class:</p> <pre><code>public class AckWaiter extends Thread { public int counter; PeerManager pm; Message m; public Object waiter; public int parentPort; public AckWaiter(PeerManager pm, Message m, int n,int parentPort) { counter = n; this.pm = pm; this.m = m; this.parentPort=parentPort; waiter=new Object(); } public synchronized void notifyAck() { counter--; notify(); } @Override public synchronized void run(){ pm.sendAllExceptMe(m); try { BufferedReader inFromClient=new BufferedReader(new InputStreamReader(pm.listener.socketMap.get(parentPort).getInputStream())); while(counter&gt;0){ wait(100); Message m=CustomMarshaller.getCustomMarshaller().unmarshal(inFromClient.readLine()); if(m==null){ continue; } m.execute(pm); } } catch (IOException | InterruptedException e1) { // TODO Auto-generated catch block e1.printStackTrace(); } waiter.notify(); return; } } </code></pre> <p>and here's the call supposed to block the thread</p> <pre><code>public synchronized void sendAllWithAck(Message m){ if(aw!=null){ throw new RuntimeException(); } aw=new AckWaiter(this,m,connectionList.size()-1,m.sender.getPort()); aw.start(); try { aw.waiter.wait(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } aw=null; } </code></pre> <p>'sendAllWithAck' should start a AckWaiter Thread, wait on the object 'waiter' that will be notified when i receive 'n' ACKs.</p> <p>The 'notifyAck' method is called by the communication layer when an ACK message is received. </p> <p>AckWaiter is a thread on his own because 'sendAllWithAck' could be called by a thread in charge of reading from a socket. I have n peers and every peer has an open socket (with a Thread handling inbound messages) for every other peer, so if i wait for ACKs in response to a message received, i wouldn't be able to read the ACK from that one peer (parentPort is the identifier of that peer so i can periodically check for ACKs inside this thread).</p> <p>I'm open to modify my architecture if this exception is due to a structural problem but i have no idea to handle it differently without modify my communication layer, and that would be a pain.</p>
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