java - Thread safe access to arraylist: two producer one consumer. Lock object is enough? -

i have 2 thread can produce value , add in arraylist, , other thread can access read value.

my problem producer can access list in same time consumer use data.

this code :

 public class commandtree  {    lock lock = new reentrantlock();  arraylist<command> cmdtosend = null; jsonobject sendcmdmap;  public commandtree(jsonobject sendcmdmap) {     this.cmdtosend = new arraylist<command>();     this.sendcmdmap = sendcmdmap; }  private synchronized void addmacrocmd(string macro, int fmt, int tgt, int sid,int count,jsonarray sli,string paramname,jsonobject params,int function) {      boolean check = false;     int = 0;      lock.lock();         try         {             for(i=0; i<cmdtosend.size(); i++)             {                 if(cmdtosend.get(i).getmacroname().equalsignorecase(macro))                 {                     check = true;                     break;                 }             }              if(check == false)             {                 cmdtosend.add(new command(macro,fmt,tgt,sid,count,function,sli));             }              if(paramname != null)             {                 if(check)                     cmdtosend.get(i).setparameter(paramname,params);                 else                     cmdtosend.get(cmdtosend.size()-1).setparameter(paramname,params);             }         }                 {             lock.unlock();         } }   private void addparameter(string macro,int fmt, int tgt, int sid,int count,jsonarray sli,string paramname,jsonobject params,int function) {     lock.lock();     try     {         this.addmacrocmd(macro, fmt, tgt, sid, count,sli, paramname,params,function);     }         {         lock.unlock();     }  }  public int getsize() {     return cmdtosend.size(); }  public void reset() {     lock.lock();     try     {         cmdtosend.clear();     }         {         lock.unlock();     }  }  /* public command getnextcommandinloop() {     return cmdtosend.; } */ public command getnextcommand(int i) {     command result;      lock.lock();     try     {         result = cmdtosend.get(i);     }         {         lock.unlock();     }      return result; }  public synchronized boolean populatecommandtree(string i,string target) throws jsonexception {     jsonobject tgtcmd = (jsonobject) sendcmdmap.get(target);     jsonobject cmdobject;      iterator<string> iter = tgtcmd.keys();      while (iter.hasnext())      {         string key = iter.next();          if(key.equalsignorecase(i))         {             //it general commands             jsonobject macro = (jsonobject)tgtcmd.opt(key);              cmdobject = (jsonobject) macro.opt("cmd");               addmacrocmd(key,cmdobject.optint("fmt"),cmdobject.optint("tgt"),cmdobject.optint("sid"),cmdobject.optint("count"),cmdobject.optjsonarray("sli"),null,null,macro.optint("function"));              return true;         }            else         {             //it parameter, have search general command              cmdobject = (jsonobject)tgtcmd.opt(key);              if(cmdobject == null)             {                 continue;             }              jsonobject parameter = cmdobject.optjsonobject("parameter");              if( parameter == null)             {                 //there isn't requested command, iterate on next 1                 continue;             }             else             {                  if(((jsonobject) parameter).optjsonobject(i) != null)                 {                     jsonobject cmdstructure = (jsonobject)cmdobject.opt("cmd");                     //we have found  command, save in commandsendcache                     addmacrocmd(key,cmdstructure.optint("fmt"),cmdstructure.optint("tgt"),cmdstructure.optint("sid"),cmdstructure.optint("count"),cmdstructure.optjsonarray("sli"),i,parameter.optjsonobject(i),cmdobject.optint("function"));                     return true;//(jsonobject)tgtcmd.opt(key);                 }                 else                 {                     continue;                 }             }         }     }      return false; }} 

i read post on case, don't understand well. thought post code in way can understand in better way.

other problem 1 producer ui thread, , worried if there problem stop ui thread times.

i thought use concurrentlinkedqueue because time need loop on list, , extract value first position, concurrentlinkedqueue don't know how can implementate loop , in way can implementate addmacrocmd method..

in case think use lock object , arraylist.

do have suggestion ? want learn in better way concurrency, not easy me :(

edit : following part of code add , remove command :

public synchronized void readsensordata(string[] sensor, string target)     {         cmdtree.reset();           for(int i=0;i<sensor.length;i++)         {             try              {                 cmdtree.populatecommandtree(sensor[i],target);             }              catch (jsonexception e)              {              }         }          writeexecutor.execute(this.writecommandtree);      }         /**      *       * @param      * @param target      * @return      * @throws jsonexception when command requested doesn't exists      */        private bytearrayoutputstream f = new bytearrayoutputstream();     executorservice writeexecutor = executors.newsinglethreadexecutor();      semaphore mutex = new semaphore(0);      volatile boolean diagnostic = false;     volatile int index = 0;      runnable writecommandtree = new runnable()     {          @override         public void run()          {             while(index < cmdtree.getsize())             {                 writecmd();                 try                  {                     mutex.acquire();                 }                  catch (interruptedexception e)                  {                     e.printstacktrace();                 }              }              sendanswerbroadcast("answer", answer);              answer = new jsonobject();             index = 0;          }      }; 

and mutex release when arrive new response .

addictional information :

the readsensordata() called when button on ux (ui thread) pressed , in same case other thread b. writecommandtree execute in executor (other thread c).

i change name of getnextcommand getcommand - getcommand(int i) called in callback of response (sometime in other thread (i'm forget function ...) , in writecmd inside writecommandtree - getsize in writecommandtree in thread c

don't headaches synchronizing list, use java standard library :

list<command> commands = collections.synchronizedlist(new arraylist<>()); 

by way, naive implementation of wrap unsafe list , add synchronized methods.