wait vs. yield?
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From: Arne Vajhøj on 6 Jun 2010 22:29 On 03-06-2010 23:05, Peter Duniho wrote: > Perhaps Java has a similar thread scheduler (and inasmuch as it may just > delegate thread scheduling to the OS, though it doesn't have to, it > would of course inherit that behavior when running Java on Windows). The Java standard does not mandate anything. But as far as I know, then all Java implementation on normal desktop/server platforms the last decade has been using native threads and not green threads. Arne
From: Ian Shef on 7 Jun 2010 15:21
Ian Shef <invalid(a)avoiding.spam> wrote in news:Xns9D8C90AB76BE7vaj4088ianshef(a)138.125.254.103: > Daniel Pitts <newsgroup.spamfilter(a)virtualinfinity.net> wrote in > news:ZkeNn.21080$7d5.5303(a)newsfe17.iad: > > <snip> >> >> I strong suggest reading Java Concurrency In Practice. >> <http://virtualinfinity.net/wordpress/technical-book-recommendations/jav >> a -concurrency-in-practice/> >> >> > > I don't have the book in front of me, but if I recall correctly: > > The book tells you to avoid yield(). It has no testable semantics, > and > may be implemented as a NO-OP. > > Instead, use sleep(...). However, don't use sleep(0), use sleep(1). > > I am at work, my book is at home. Maybe someone with immediate access > to the book can comment? A follow-up to my own follow-up... In the book by Brian Goetz with Tim Peierls, Joshua Bloch, Joseph Bowbeer, David Holmes and Doug Lea, Java Concurrency in Practice, 6th Printing, March 2008 Footnote 5 on page 218 (Section 10.3.1 Starvation) "The semantics of Thread.yield (and Thread.sleep(0)) are undefined [JLS 17.9]; the JVM is free to implement them as no-ops or treat them as scheduling hints. In particular, they are not required to have the semantics of sleep(0) on Unix systems � put the current thread at the end of the run queue for that priority, yielding to other threads of the same priority � though some JVM implementations yield in this way." In the book by Joshua Bloch, Effective Java, Second Edition, 4th Printing, September 2008 Page 287 (Item 72: Don't depend on the thread scheduler) "Thread.yield has no testable semantics." .... "In the first edition of this book, it was said that the only use most programmers would have for Thread.yield was to artificially increase the concurrency for testing. The idea was to shake out bugs by exploring a larger fraction of the program's statespace. This technique was once quite effective, but it was never guaranteed to work. It is within specification for Thread.yield to do nothing at all, simply returning control to its caller. Some modern VMs actually do this. Therefore, you should use Thread.sleep(1) instead of Thread.yield for concurrency testing. Do not use Thread.sleep(0), which can return immediately." So JCP has part of the information, but EJ goes into more detail and is what I was remembering. I have both books and I am trying to learn from them, but I don't necessarily remember which nuggets of information are from which book. |