Forwarding to core-libs.
- Kurchi
-------- Original Message --------
Subject: Latency in starting threads on Mac OS X
Date: Tue, 16 Apr 2013 15:57:06 +0300
From: Dr Heinz M. Kabutz <he...@javaspecialists.eu>
Organization: JavaSpecialists.eu
To: macosx-port-...@openjdk.java.net
Good day my fellow Mac OS X users!
Yesterday, whilst teaching my Concurrency Specialist Course, I wanted to
demonstrate to my class how slow it was starting threads and how much
better it is to use a FixedThreadPool. The question that I wanted to
answer was: How many microseconds does it take on average to start a
simple thread and what is the maximum time it could take?
We all know that it can take in the milliseconds range to do the following:
Thread t = new Thread(); // even without it actually doing anything
t.start();
This is one of the reasons why the fixed thread pool only starts the
threads as we submit jobs to it, since the up-front cost might not be
worth the wait.
But how long do you think the *maximum* was that I had to wait for
t.start() to return? 100ms? 200ms?
Actually, the longest I had to wait turned out to be about 250 seconds.
Yes. That is *seconds*, not *milliseconds*. Just to start a single thread.
This is most certainly a bug in the OpenJDK on Mac OS X. We did not see
this behaviour on Linux nor on Windows 7.
The bug started in OpenJDK 1.7.0_06. Prior to that it hardly ever took
longer than 30ms to start a single thread.
java version "1.7.0_05"
heinz$ java ThreadLeakMac2
time = 1, threads = 4
time = 2, threads = 346
time = 4, threads = 7378
time = 7, threads = 9614
time = 12, threads = 10027
time = 14, threads = 10063
time = 17, threads = 26965
time = 38, threads = 27013
time = 39, threads = 452053
java version "1.7.0_06"
heinz$ java ThreadLeakMac2
time = 1, threads = 6
time = 2, threads = 256
time = 6, threads = 373
*snip*
time = 111, threads = 42592
time = 200, threads = 49419
time = 333, threads = 58976
*snip*
time = 3245, threads = 202336
time = 3706, threads = 203702
*snip*
time = 5835, threads = 267872
time = 6455, threads = 269238
time = 9170, threads = 270603
In my code, I make sure that the thread has stopped before creating the
next one by calling join().
public class ThreadLeakMac2 {
public static void main(String[] args) throws InterruptedException {
long threads = 0;
long max = 0;
while(true) {
long time = System.currentTimeMillis();
Thread thread = new Thread();
thread.start(); // should finish almost immediately
time = System.currentTimeMillis() - time;
thread.join(); // short delay, hopefully
threads++;
if (time> max) {
max = time;
System.out.println("time = " + time +
", threads = " + threads);
}
}
}
}
This would be another nice test case for Alexey's concurrency stress
test harness.
(I also posted this to the concurrency-interest list.)
Regards
Heinz
--
Dr Heinz M. Kabutz (PhD CompSci)
Author of "The Java(tm) Specialists' Newsletter"
Sun Java Champion
IEEE Certified Software Development Professional
http://www.javaspecialists.eu
Tel: +30 69 75 595 262
Skype: kabutz
