java - Selector.select() does not block -

sorry, searched around 2 days before had post question. there similar questions, none of them helped me.

i trying create simple chat application client uses (non-nio) socket connect server listens nio serversocketchannel. server uses selector. until first client connects, selector.select() method blocked, expected. after first client connects, selector.select() not block , returns immediately. causes while loop run continuously.

sorry, i've pasted entire code can copy-paste , run it. i've started java, help/pointers appreciated. thank you.

p.s.: right now, client sends serialized object (message object) on socket connection , server reads it. since connection non-blocking, serialized object pre-fixed object size (in bytes) before sent server. allows server read next "x" bytes , un-serialize message object. server code work in progress.

client code----------

import java.io.bufferedinputstream; import java.io.bufferedoutputstream; import java.io.bytearrayinputstream; import java.io.bytearrayoutputstream; import java.io.dataoutputstream; import java.io.objectoutputstream; import java.io.objectinputstream; import java.net.inetaddress; import java.net.socket; import java.net.unknownhostexception; import java.nio.bytebuffer;  public class chatclient {      void go(){         user u = new user();         u.setname("usera");         try{             u.setinet(inetaddress.getlocalhost());         }catch (unknownhostexception ex){             system.out.println(ex);             return;         }         message m = new message();         m.settype(3);         m.settext("this 1st message.");         m.setfromuser(u);         try{             socket sock = new socket (inetaddress.getlocalhost(), 5000);             dataoutputstream dataout = new dataoutputstream(sock.getoutputstream());              bytearrayoutputstream bytetemp = new bytearrayoutputstream();             objectoutputstream objout = new objectoutputstream (bytetemp);             objout.writeobject(m);             objout.flush();             objout.close();              byte[] bytemessage = bytetemp.tobytearray();             bytebuffer bb = bytebuffer.allocate(4);             bb.putint(bytemessage.length);             byte[] size = new byte[4];             size = bb.array();             system.out.println("object size = "+bytemessage.length); //370              bytearrayoutputstream byteout = new bytearrayoutputstream();             byteout.write(size);             byteout.write(bytemessage);              byte[] finalmessage = byteout.tobytearray();             dataout.write(finalmessage,0,finalmessage.length);             dataout.flush();             system.out.println("flushed out");         }catch (exception ex){             system.out.println(ex);         }     }      public static void main (string args[]){         new copyofchatclient().go();     } } 

server code ---------------

    import java.io.bytearrayinputstream;     import java.io.ioexception;     import java.io.objectinputstream;     import java.net.inetsocketaddress;     import java.nio.bytebuffer;     import java.nio.channels.selectionkey;     import java.nio.channels.selector;     import java.nio.channels.serversocketchannel;     import java.nio.channels.socketchannel;     import java.util.iterator;     import java.util.set;     import java.util.concurrent.locks.reentrantlock;      public class copyofchatserver {         object a, b;//dummy objects synchronization         socketchannel clientsock=null;         selector selector;         selectionkey key;          void go(){             try{                 a=new object();//dummy objects synchronization                 b=new object();//dummy objects synchronization                 serversocketchannel serversock = serversocketchannel.open();                 serversock.socket().bind(new inetsocketaddress(5000));                 //note: serversocketchannel blocking, each new connection returned accept() made non-blocking (see below)                 selector = selector.open();                 new thread(new selectorthread()).start(); //start selectorthread                 int i=0;                 while (true){                                    clientsock = serversock.accept();                     if (clientsock!=null){                                           clientsock.configureblocking(false); //the default client socket returned accept() blocking. set non-blocking.                                                   synchronized (b){                             selector.wakeup();                             synchronized (a){                                 key = clientsock.register(selector, selectionkey.op_read);  //register new client socket selector                                   key.attach(clientsock);                             }//sync(a)                         }//sync(b)                                       i++;                     }                     system.out.println("here");                 }//while(true)              }catch (exception ex){                 system.out.println(ex);             }         }          class selectorthread implements runnable{             set <selectionkey> selectedkeys;             int readychannels;             public void run(){                 while (true){                                        try {                             synchronized(a){                                 system.out.println("1. selector trying select");                                 readychannels = selector.select();//note: select() blocking ?? not block. behaves non-blocking                                 system.out.println("2. selector has selected");                             }//sync                              synchronized (b){                                 //just wait till registration done in main thread                             }                              if (readychannels == 0) continue; //even if select() blocking, check handle suprious wake-ups                             system.out.println("readychannels>0");                             selectedkeys = selector.selectedkeys();                             iterator<selectionkey> keyiterator = selectedkeys.iterator();                             while (keyiterator.hasnext()){                                 selectionkey key = keyiterator.next();                     keyiterator.remove();//added after first answer question                                 if (key.isreadable()){                                     system.out.println("3. got incoming data");                                     socketchannel tempsock = (socketchannel)key.attachment();                                     bytebuffer bb=bytebuffer.allocate(8000);                                     int bytesread=tempsock.read(bb);                                     system.out.println("4. bytes read = "+bytesread);                                     if (bytesread>4){                                         bb.flip();                                         bb.rewind();                                          int size = bb.getint();                                         system.out.println("5. size of object = "+size);                                         byte[] objin = new byte[size];                                         (int i=0;i<size;i++){                                             objin[i]=bb.get();                                         }                                         bb.compact();                                          bytearrayinputstream bin= new bytearrayinputstream(objin);                                         objectinputstream objstream= new objectinputstream(bin);                                         message temp1 = (message) objstream.readobject();                                         system.out.println("6. read object back");                                         system.out.println(temp1.getfromuser().getname());                                     }                                 }                             }                             selectedkeys.clear();                          } catch (ioexception e) {                             e.printstacktrace();                         } catch (classnotfoundexception e) {                             // todo auto-generated catch block                             e.printstacktrace();                         }                   }             }         }          public static void main (string args[]){             new copyofchatserver().go();         }     } 

message class ----

import java.io.serializable;  public class message implements serializable{     private int type;      private user fromuser;     private user touser;     private string text;      public int gettype() {         return type;     }     public void settype(int type) {         this.type = type;     }     public user getfromuser() {         return fromuser;     }     public void setfromuser(user fromuser) {         this.fromuser = fromuser;     }     public user gettouser() {         return touser;     }     public void settouser(user touser) {         this.touser = touser;     }     public string gettext() {         return text;     }     public void settext(string text) {         this.text = text;     }  }    

user class --------

import java.io.serializable; import java.net.inetaddress;  public class user implements serializable{     private string name;     private inetaddress inet;       public string getname() {         return name;     }     public void setname(string name) {         this.name = name;     }     public inetaddress getinet() {         return inet;     }     public void setinet(inetaddress inet) {         this.inet = inet;     }    } 

you must put

keyiterator.remove() 

after

keyiterator.next() 

the selector doesn't remove selectedkeys() itself.

nb don't need attach channel key attachment. can key.channel().