java - Why don't these threads run in sequence? -

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• synchronized block not working 8 answers

i have difficulty understanding synchronized , reentrant lock. here small program experimenting with:

import java.util.concurrent.executorservice; import java.util.concurrent.executors;  public class reentr {      public static void main(string[] args) {         executorservice eservice = executors.newfixedthreadpool(2);         (int = 1; <= 2; i++) {             eservice.execute(new process());         }          try {             thread.sleep(1);         } catch (interruptedexception e) {             // todo auto-generated catch block             e.printstacktrace();         }          eservice.shutdown();     }  }  class process implements runnable {     int count = 0;      @override     public void run() {          processtest();     }      public synchronized void processtest() {         try {             (int = 1; <= 2; i++) {                 count += i;                 system.out.println("count value " + thread.currentthread().getname() + " " + count);             }         } {             system.out.println("count " + thread.currentthread().getname() + " " + count);         }     }  } 

the output was:

count value pool-1-thread-2 1 count value pool-1-thread-1 1 count value pool-1-thread-2 3 count pool-1-thread-2 3 count value pool-1-thread-1 3 count pool-1-thread-1 3 

if see in output 2 thread in synchronized block. under impression 1 thread has complete execution of synchronized method, after other thread enter method.

ideally, expecting result this

count value pool-1-thread-1 1 count value pool-1-thread-1 3 count pool-1-thread-1 3 count value pool-1-thread-2 1 count value pool-1-thread-2 3 count pool-1-thread-2 3 

i have replaced synchronized method synchronized block , re-entrant locks. however, still have same output. missing?

the 2 threads not synchonizing on same object.

you have 2 different instances of process (as aside; should name classes capital letter). synchronized keyword equivalent to:

public void processtest() {   synchronized(this) {     // etc..   } } 

if want 1 thread run after other, must synchronize on same object. if did this, example:

class process implements runnable {   // note static   private static final object lock = new object();    public void processtest() {     synchronized(lock) {       // code     }   } } 

then code have 1 thread run after other. way pass lock objects constructor, or same instance of semaphore, etc.