multithreading - Java ExecutorService:- Notify a thread to wake up when an event occurs -

i have manager class multiple threads register (used uuid generate unique identifiers per requests), gives payload process , corresponding responses manager. using java.util.concurrent.executorservice launch multiple threads. here implementation testing manager functionality-

public class managertest {     public static void main(string[] args) {         try {             manager mymanager = new manager();             // start listening messages different threads             mymanager.consumemessages();             int num_threads = integer.parseint(args[0]);             executorservice executor = executors.newfixedthreadpool(num_threads);              (int = 0; < num_threads; i++) {                 // class implementation given below                 runnable worker = new myrunnable(mymanager);                 executor.execute(worker);             }             executor.shutdown();             // wait until threads finish             while (!executor.isterminated()) {              }             system.out.println("\nfinished threads");              mymanager.closeconnection();          } catch (ioexception | timeoutexception e) {             e.printstacktrace();         }     } } 

here implementation of myrunnable class

class myrunnable implements runnable {     private manager managerobj;     public myrunnable(manager managerobj) {         this.managerobj = managerobj;     }      @override     public void run() {              try {             random rand = new random();             int  n = rand.nextint(35);             string requestid = uuid.randomuuid().tostring();             managerobj.registerrequest(requestid, n);             managerobj.publishmessage(requestid);             // want avoid while loop             while( ! managerobj.getrequeststatus(requestid)){              }             int response = managerobj.getrequestresponse(requestid);             // else             managerobj.unregisterrequest(requestid);          } catch (ioexception e) {             e.printstacktrace();         }     } } 

the manager process requests , depending on payload response of request can take varying amount of time. whenever manager gets response sets requests status true calling function setrequeststatus(requestid). after thread exit while loop , continues execution.

the code if working fine, thread doing work needed continuously looping on while loop until condition met.

is way make thread sleep after sending requests manager, , manager signals thread wake when response ready.

pardon me if sounds simple someone, newbie java , java-threading interface.

that's fine, used simple questions, , question written , has reasonable problem solve, see lot worse here every day, people not knowing want, how ask it, etc.

so, doing busy-spin-loop, , bad thing do, because a) consumes full cpu core per thread, , b) keeps cpu busy, means stealing processing time other threads might have useful work do.

there number of ways can solve this, list them worst best.

• the simplest way improve code invoke java.lang.thread.sleep(long millis) method, passing 0 parameter. known "yield" operation, , means "if there other threads have useful work do, let them run, , return me once done." marginally better busy-spin-looping because still consume 100% cpu. benefit consume cpu while other threads not have do, @ least not slow other things down.

• the next best, still not smart, way improve code invoking java.lang.thread.sleep(long millis) method passing 1 parameter. known "pass" operation, , means "release remainder of time-slice other threads might have useful work do". in other words, remainder of time-slice forfeited, if no useful work needs done in entire system. bring cpu consumption down zero. disadvantages a) cpu consumption above zero, b) machine not able go low-power sleep mode, , c) worker thread less responsive: pick work on timeslice boundary.

• the best way solve problem using synchronization mechanism built java, explained in answer: https://stackoverflow.com/a/5999146/773113 not consume 0 cpu, allow machine go low power mode while waiting.

• to solve problem general case, don't want wait until condition, pass information work done, use blockingqueue. (https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/blockingqueue.html) blocking queue works using java built-in synchronization mechanism and allows 1 thread pass information another.