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<span style="font-family:Verdana; color:#000000; font-size:10pt;"><div>Could you elaborate on that worked "backed"? Do you mean a single thread created by a java application is implemented with a single pthread?</div><div><br></div><div>Due to the micro-kernel "feature" in Windows (last I checked about 10 years ago -- I doubt any thing has changed), windows threading is ugly. In contrast to most linux implementations, micro-kernel architectures like windows move a lot of functionality out of the kernel into special auxiliary (aux) processes. The result of this is horrible! Instead of doing a single user-mode to kernel-mode context switch for I/O (for example), windows often does a process context switch to the aux system process and that aux process then does a user-to-kernel context switc
h to execute the kernel mode function (and of course we have to context switch back to the aux process and then back to the application process). </div><div><br></div><div>This is in contrast to a single user-to-kernel mode context switch in Linux (can anyone confirm this?).</div><div><br></div><div>But wait! It gets uglier!</div><div>If you are writing multi-threaded applications in windows, every thread you create in your application also allocates precious kernel mode thread-control-block memory *AND* a shadow kernel thread! Yikes! This makes sense when you think about it: If you are doing parallel asynchronous threading in your application and are making requests that are implemented in a different (aux) system process, that aux process must also have shadow threads run in paral
lel too. Otherwise there would be no benefit to multi-threading in an application if all there threads had to wait on the kernel and aux processes.</div><div><br></div><div>If you use the free tools for process monitoring, you can see the gazillions of threads that common apps like Microsoft Outlook use. While working for Microsoft, we were strongly encouraged to use thread-pools so we don't have acres of idle threads like some Microsoft apps have.</div><div><br></div><div>Now as I recall, most Linux applications create processes very efficiently and the implementation of the create-thread function in linux is very similar to the create-process feature in terms of elapse time, CPU time and processor time. Can anyone confirm this? This makes me wonder, since processes are relatively heavy
weight compared to threads, if Linux thread-creation could be optimized.</div><div><br></div><div>Because Dave Cutler wrote VAX/VMS and (much later) Windows, creating processes in Windows is very slow. The way it worked in VAX/VMS (and probably windows) is that the entire process image is laid out on disk and the process is swapped (or paged in in the case of windows) on demand. This is very slow compared to the Linux/Unix strategy.</div><div><br></div><div>Hurray for faster disks and faster silicon! </div><div><br></div><div><br></div>
<blockquote id="replyBlockquote" webmail="1" style="border-left: 2px solid blue; margin-left: 8px; padding-left: 8px; font-size:10pt; color:black; font-family:verdana;">
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-------- Original Message --------<br>
Subject: Re: [seajug] In Java 7 (or 8) is it still more expensive to<br>
create/destroy threads instead of using a thread pool?<br>
From: Mat Gessel <<a href="mailto:mat.gessel-***@public.gmane.org">mat.gessel-***@public.gmane.org</a>><br>
Date: Fri, April 18, 2014 2:15 pm<br>
To: <a href="mailto:seajug-***@public.gmane.org">seajug-***@public.gmane.org</a><br>
<br>
<span style="display:none"> </span> <div id="ygrp-mlmsg" style="position:relative;"> <div id="ygrp-msg" style="z-index: 1;"> <div id="ygrp-text"> <div></div><div dir="ltr"><div>I can't speak to Windows, but for Mac OS and Linux, each Java thread is backed by a native Posix thread (pthread). This has not changed in recent JREs. <br><br></div><div>You can see this in Linux by invoking "top" and pressing Shift-H. This shows "lightweight processes", a.k.a. threads. <i>Tip</i>: you can take the process id (PID), convert it to hex and correlate to the native id (NID) in the thread dump generated by jstack. Great way to track down infinite loops. <br> </div><div><br></div>-= Mat<br><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Apr 18, 2014 at 10:37 AM, D
avid Karr <span dir="ltr"><<a href="mailto:davidmichaelkarr-***@public.gmane.org" target="_blank">davidmichaelkarr-***@public.gmane.org</a>></span> wrote:<br> <blockquote class="gmail_quote" style="border-left:1px #ccc solid;"> <u></u> <div> <span> </span> <div> <div> <div> <div></div><div dir="ltr"><div><div>It is "common knowledge" that simple parallel processing should use a thread pool instead of creating and destroying threads on the fly, if performance is the only concern.<br> <br></div>However, it's reasonable to ask every once in a while, has Java thread creation/destruction overhead decreased to a point where the performance difference is less or negligible?<br> <br></div>Has anyone done experiments with either Java 7 or Java 8 to see what the tradeoffs are today?<br></div> <div></div> </d
iv><br></div></div></div></blockquote></div>Mat Gessel<br><a target="_blank" href="http://www.asquare.net">http://www.asquare.net</a> </div></div></div></div> <div></div> </div> <div style="color: #fff; height: 0;"></div> <style type="text/css">
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