java - Difference between notify() and notifyAll() -

java - Difference between notify() and notifyAll() -

i know similar questions have been discussed in site, have not still got farther aid considering specific example. can grasp difference of notify() , notifyall() regarding thread "awakeining" in theory cannot perceive how influence functionality of programme when either of them used instead of other. hence set next code , know impact of using each 1 of them. can start give same output (sum printed 3 times).

how differ virtually? how modify program, in order applying notify or notifyall play crucial role functionality (to give different results)?

task:

class mywidget implements runnable { private list<integer> list; private int sum; public mywidget(list<integer> l) { list = l; } public synchronized int getsum() { homecoming sum; } @override public void run() { synchronized (this) { int total = 0; (integer : list) total += i; sum = total; notifyall(); } }

}

thread:

public class myclient extends thread { mywidget mw; public myclient(mywidget wid) { mw = wid; } public void run() { synchronized (mw) { while (mw.getsum() == 0) { seek { mw.wait(); } grab (interruptedexception e) { e.printstacktrace(); } } system.out.println("sum calculated thread " + thread.currentthread().getid() + " : " + mw.getsum()); } } public static void main(string[] args) { integer[] array = { 4, 6, 3, 8, 6 }; list<integer> integers = arrays.aslist(array); mywidget wid = new mywidget(integers); thread widthread = new thread(wid); thread t1 = new myclient(wid); thread t2 = new myclient(wid); thread t3 = new myclient(wid); widthread.start(); t1.start(); t2.start(); t3.start(); }

}

update: write explicitly. result same whether 1 uses notify or notifyall: sum calculated thread 12 : 27 sum calculated thread 11 : 27 sum calculated thread 10 : 27

therefore question: difference?

the difference subtler illustration aims provoke. in words of josh bloch (effective java 2nd ed, item 69):

... there may cause utilize notifyall in place of notify. placing wait invocation in loop protects against accidental or malicious notifications on publicly accessible object, using notifyall in place of notify protects against accidental or malicious waits unrelated thread. such waits otherwise “swallow” critical notification, leaving intended recipient waiting indefinitely.

so thought must consider other pieces of code entering wait on same monitor waiting on, , other threads swallowing notification without reacting in designed way.

other pitfalls apply well, can result in thread starvation, such several threads may wait different conditions, notify happens wake same thread, , 1 status not satisfied.

even though not related question, sense of import quote conclusion (emphasis original author):

in summary, using wait , notify straight programming in “concurrency assembly language,” compared higher-level language provided java.util.concurrent. there seldom, if ever, reason utilize wait , notify in new code. if maintain code uses wait , notify, create sure invokes wait within while loop using standard idiom. notifyall method should used in preference notify. if notify used, great care must taken ensure liveness.

java multithreading notify