April 2009 - Darwin-dev - lists.apple.com

Re: Are kqueue events "round robin"?
by Påhl Melin 08 Apr '09

08 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=F8TvpoeIGBQupHiMG/kN/5hSi+5tgxwp7QxtIlHITX4=; b=XvMO+l2DNxFw2QK0UsYXBp/UUfWvceGKq4BNxgzSRudecJTBS8/Z7QY+4Q7olcyxWQ XulQNuIVUvP9r6gUPRsuOY5IeYRvndSekx4iz5F/5Ai92c5CjVcnQmBGWljoMYZ/ci5d c73T102794GzWEkyaCRp9mueayIIU1eMS1lp0= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=FqYgq1gAKzC9ID/IJOM6GsqtEg16+6Wguciz58RAuaV4M778fvS7v1hXI/6yUc8vLB SdAXGr2xOnY6TA2jmx59jUbrkObWYNuxaye2xsxMzVkTlmhO7SG303k0oX06LkdnWusL BIyz49g7xBSc3Dr/BxwxAZ2AapKkWPtHETOXs= 2009/4/7 Terry Lambert <tlambert(a)apple.com>: > <http://people.freebsd.org/~jlemon/papers/kqueue_freenix.pdf> > > There are also 14 other papers referencing that one, which discuss things > like a Linux implementation. > > A useful search engine network to bookmark for CS papers is Citeseer: > <http://citeseer.ist.psu.edu>. Thanks Terry, That document clear up most or all of my questions I think, after a brief skimming! And the search engine found the paper right away on a search on kqueue. / Påhl _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: GDB versions.
by Jonas Maebe 07 Apr '09

07 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com On 09 Feb 2009, at 21:12, Pascal wrote: Jonas _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Though I want to port GDB for Ada language from GNAT GPL: https://libre.adacore.com/dynamic/download_page (directory sources) It is based on FSF version 6.8. This version hasn't Mac extensions to build properly. How can I get this version building on Mac OS X ? Download the latest version from GDB CVS. It has support for Mac OS X/ x86 (both 32 and 64 bit; no PowerPC support though), although there are still some rough edges: * calling functions from within gdb will often crash, because gdb does not align the stack to 16 bytes before calling the function * when the debugged program finishes its execution, gdb crashes Those are the two issues I encountered, but other than that it already works fairly well (I'm not using it for debugging Ada though). This email sent to site_archiver(a)lists.apple.com

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Re: Are kqueue events "round robin"?
by Terry Lambert 07 Apr '09

07 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com You are totally right. I'm probably overthinking this, but I haven't seen much detailed information on kqueue:s on Google, books and elsewhere and I didn't want to spend unnecessary time implementing something bound to fail. <http://people.freebsd.org/~jlemon/papers/kqueue_freenix.pdf> -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Apr 7, 2009, at 2:47 AM, Påhl Melin <listor.pm(a)gmail.com> wrote: 2009/4/6 A.M. <agentm(a)themactionfaction.com>: On Apr 6, 2009, at 7:12 AM, Påhl Melin wrote: I would expect the kqueue not to be filled up with EVFILT_READ and EVFILT_WRITE events, but to have only one of each whenever the buffers are "ready". But the question is if I'm guaranteed to have alternating read and write events? Or if I get starvation of any kind? I don't see anything about this matter in the man pages so I'm curious if it's specified at all? There are no guarantees made, but in my usage, I have not experienced starvation under conditions similar to yours. You may be overthinking this. Just try it and you can address starvation later, if it occurs. There are also 14 other papers referencing that one, which discuss things like a Linux implementation. A useful search engine network to bookmark for CS papers is Citeseer: <http://citeseer.ist.psu.edu >. This email sent to site_archiver(a)lists.apple.com

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Re: Are kqueue events "round robin"?
by Påhl Melin 07 Apr '09

07 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=1w0NHlQBk3NMxa039yXYB9/lVwn/XUcS8s3forDCePU=; b=A/VB03fpFlyNWhhYXz062rpHCPir37sTsibDQmzIkr7AOjV5dECtgxNpGkCx++oN/F wU2BUljDS/FY/tmdRhxP0i5ejsB9wlxGUxu7JaZMkeNOEG3U2b8KYyfREodeS6JJMYLO jpVArE+ym2Brz2WXdQxjd79t2KDlmN5PO/SFI= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=RLyxGD83Gkjolt3qMZE9qgb6k+dDNzLo/CaHxQMo0Ir1qE3Gujg6WMOJ5Kb999C5Vp jvWl9xauOThgJXAP6+1JhzAMQNC5LuekGlIUreUlwr23hDTlKz2qYUQSun4yNcVoI7Ej KD/Mi81uxZy5s7whHeVcln8jB4pg9YdpEsXvE= 2009/4/6 A.M. <agentm(a)themactionfaction.com>: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > > On Apr 6, 2009, at 7:12 AM, Påhl Melin wrote: >> >> I would expect the kqueue not to be filled up with EVFILT_READ and >> EVFILT_WRITE events, but to have only one of each whenever the buffers >> are "ready". But the question is if I'm guaranteed to have alternating >> read and write events? Or if I get starvation of any kind? I don't see >> anything about this matter in the man pages so I'm curious if it's >> specified at all? > > There are no guarantees made, but in my usage, I have not experienced > starvation under conditions similar to yours. You may be overthinking this. > Just try it and you can address starvation later, if it occurs. You are totally right. I'm probably overthinking this, but I haven't seen much detailed information on kqueue:s on Google, books and elsewhere and I didn't want to spend unnecessary time implementing something bound to fail. >>> I haven't experienced any event starvation situation, but in case you have, >>> the best approach would be to implement an array over kqueue. Simply read >>> more than one event into your own queue and you can algortithmically decide >>> which events to process (and then remove them from the array- obviously it's >>> no longer a queue). But don't waste time implementing this approach >>> unless you are indeed experiencing starvation. >> >> Thanks, I hadn't really considered returning multiple events and make >> my own decision. But it would of course be easier if a reasonable >> decision was already made by the kevent() call. > > If you only have one socket (thus, only one kqueue ident filter), I wouldn't > bother with this suggestion at all. > >>> Since one thread can only do so much, if you have lots of socket or sources, >>> then you may want to break their processing into separate thread (kqueue is >>> thread-safe and works well across multiple threads). Even a single socket >>> read and write events could be broken out across threads. >> >> That's interesting. I what sense is kqueue thread safe? Can I wait on >> the same kqueue in two different threads, each calling kevent() or do >> I make two kqueue:s, one with a read filter and the other queue with a >> write event on the same socket descriptor? > > You can add filters to kqueue from different threads, kqueue-block on the > same events on different threads, use multiple kqueues from different > threads, block on the same ident with different filters. It all works. Wow, I would never imagine kqueue:s being _that_ "robust". I would certainly have added multiple mutex blocks etc. to do anything of the above! > In your design, if the messages are heavyweight, you could have multiple > consumer threads waiting on the same socket events and process them > immediately. However, I wouldn't recommend adding threads if you don't need > them. If I'm successful, the message system will be used quite heavily, potentially in the range of tens of thousands of messages being processed per second on the server side. But for now, a single worker thread design will be just fine. It's better to have something working first. Thanks a lot for the encouraging information. It's time for some implementation now... > I pity the fool that uses select(). :-) > Cheers, > M > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v2.0.10 (Darwin) > > iEYEARECAAYFAknaXbYACgkQqVAj6JpR7t6AugCffFzkZHLIv8tkL9dSPPY/W1Cn > qesAnjvSt6VYnyKeeSN65d4gA94c4ikw > =csm1 > -----END PGP SIGNATURE----- _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: Double Fault Causes?
by Eli Bach 06 Apr '09

06 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:from:to :in-reply-to:content-type:content-transfer-encoding:subject :mime-version:date:references:x-mailer; bh=Z/dHN7LnuCer86OaXdIpjfcKsH7gEmCe1LaTe73uimI=; b=aP13B1svlTTLajJY+HrI5BeDt62JRaSP2wfXp8dmrrQyuVm98cpWgy98tGrFHqAG2z 9dCrunNZ0HqZAy+LZFlZpPkyRvyN+mhwQVF9vqvK0I/AfLOTNzTvMj3XYdRfVntc9JI1 DmaOd3TtIf66+8deqxslf2sy3Inco84POvSZc= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:from:to:in-reply-to:content-type :content-transfer-encoding:subject:mime-version:date:references :x-mailer; b=Dr5WFHbJKwtHI/lhXfEgAoVvEE/ppovbX5vjxpmJgAs7fcfDhNDpwTDCAal34PgrHN F2+kOAVlUrob3yVjdcTUFtil2tGePOpKT+2VcmSmbBGZAG5BJRsjyuJ61GD0hYkAeNpN baaYwmDmLm/YTHxIJe5AVK+k/hF3ZgiSi7/RQ= On Apr 6, 2009, at 11:38 AM, Duane Murphy wrote: >From a bit of archive reading, it appears that a double fault is classically a stack overflow. However, the stack that the double fault is reported on is clearly not overflowed. The resulting back trace is actually very reasonable. Eli _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… What other problems should I be looking for in determining the cause of the double fault? I recall from my University days that the 'classic' reason for a double-fault in a disk driver would be that the OS is processes a page fault by paging in some VM from disk, and when the disk driver actually tries to read it in, the driver touches some memory which causes another page fault (hence, a double-page fault). Could some memory your driver wants to use not be locked in RAM (gah, I forget the right term for this)? This email sent to site_archiver(a)lists.apple.com

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Unsubscribe
by Don Witt 06 Apr '09

06 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Organization: Cylogistics Thread-index: Acm26nzZ3qR3xSnbR6ezQoFGwnGpVgAADbjg -----Original Message----- From: darwin-dev-bounces+witt=cylogistics.com(a)lists.apple.com [mailto:darwin-dev-bounces+witt=cylogistics.com@lists.apple.com] On Behalf Of darwin-dev-request(a)lists.apple.com Sent: Monday, April 06, 2009 12:04 PM To: darwin-dev(a)lists.apple.com Subject: Darwin-dev Digest, Vol 6, Issue 84 Send Darwin-dev mailing list submissions to darwin-dev(a)lists.apple.com To subscribe or unsubscribe via the World Wide Web, visit http://lists.apple.com/mailman/listinfo/darwin-dev or, via email, send a message with subject or body 'help' to darwin-dev-request(a)lists.apple.com You can reach the person managing the list at darwin-dev-owner(a)lists.apple.com When replying, please edit your Subject line so it is more specific than "Re: Contents of Darwin-dev digest..." Today's Topics: 1. Re: Run daemon from installer as root (Iceberg-Dev) 2. Re: Run daemon from installer as root (Rakesh Singhal) 3. Re: Are kqueue events "round robin"? (P?hl Melin) 4. Re: Run daemon from installer as root (Rakesh Singhal) 5. Double Fault Causes? (Duane Murphy) ---------------------------------------------------------------------- Message: 1 Date: Mon, 6 Apr 2009 00:54:41 +0200 From: Iceberg-Dev <dev.iceberg(a)gmail.com> Subject: Re: Run daemon from installer as root To: Darwin Dev <darwin-dev(a)lists.apple.com> Message-ID: <9E1D99CF-85BA-42C3-A264-B63A03474AEA(a)gmail.com> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed On Apr 5, 2009, at 5:27 PM, Duane Murphy wrote: > --- At Sun, 5 Apr 2009 20:03:42 +0530, Rakesh Singhal wrote: > >> Hi all, >> >> I have created an installer for my daemon application. I want my >> daemon >> to run as root after installation. Before installation I used to run >> daemon using "sudo launchctl load /Library/LaunchDaemons/ >> com.mycompany.mydaemon.plist". In installer I tried using run >> command or >> run script but it works only in 10.4.11 ppc but not with 10.5.4 >> intel. I >> want to set some file permissions/ownerships also but it doesnt work. >> Installer can be run only from admin users. Is there anyway to run >> daemon as root using command or script? > > This is not a limitation of the installer. This is a limitation of the > sh (and perl). Well, not really a limitation, it's a security feature. > Some script interpreters will refuse to run a script as root as a > security precaution. I don't recall the exact details about when this > choice is made or how to overcome it. > > My choice for overcoming the problem was to choose a different > interpreter (python). I suppose it's just a matter of time before that > door is closed also. > > I'd like to know what the alternatives are so that scripts within an > installer can be run with Administrator/root privileges. Just in case, a simple solution is probably to: 1) Be sure that the installer requires an admon/root authentication. 2) Use sudo to call launchctl even from the shell script. ------------------------------ Message: 2 Date: Mon, 6 Apr 2009 12:25:51 +0530 From: Rakesh Singhal <rakesh.singhal(a)gmail.com> Subject: Re: Run daemon from installer as root To: duanemurphy(a)mac.com, darwin-dev(a)lists.apple.com Message-ID: <bbf18850904052355q42fa27aauace063307cbe036d(a)mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" Hi Duane, I am using InstallAnyWhere to create installer. I am trying using excuting commands or script but I am not able to do it. But I think, I will have to use "sudo launchctl load /Library/LaunchDaemons/com.mycompany.mydaemon.plist" to load my daemon and run it. Is it possible that when installer execute this command or script, it can pop-up for authentication? Please advice me. Regards Date: Sun, 5 Apr 2009 08:27:48 -0700 From: "Duane Murphy" <duanemurphy(a)mac.com> Subject: Re: Run daemon from installer as root To: "Darwin Dev" <darwin-dev(a)lists.apple.com> Message-ID: <20090405152748.1674996337(a)mini.internal.murphyslogic.com> Content-Type: text/plain; charset=ISO-8859-1 --- At Sun, 5 Apr 2009 20:03:42 +0530, Rakesh Singhal wrote: >Hi all, > >I have created an installer for my daemon application. I want my daemon >to run as root after installation. Before installation I used to run >daemon using "sudo launchctl load /Library/LaunchDaemons/ >com.mycompany.mydaemon.plist". In installer I tried using run command or >run script but it works only in 10.4.11 ppc but not with 10.5.4 intel. I >want to set some file permissions/ownerships also but it doesnt work. >Installer can be run only from admin users. Is there anyway to run >daemon as root using command or script? This is not a limitation of the installer. This is a limitation of the sh (and perl). Well, not really a limitation, it's a security feature. Some script interpreters will refuse to run a script as root as a security precaution. I don't recall the exact details about when this choice is made or how to overcome it. My choice for overcoming the problem was to choose a different interpreter (python). I suppose it's just a matter of time before that door is closed also. I'd like to know what the alternatives are so that scripts within an installer can be run with Administrator/root privileges. ...Duane

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Double Fault Causes?
by Duane Murphy 06 Apr '09

06 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com I'm getting a double fault in a disk driver that I am building. I'm working on more detailed debugging. >From a bit of archive reading, it appears that a double fault is classically a stack overflow. However, the stack that the double fault is reported on is clearly not overflowed. The resulting back trace is actually very reasonable. What other problems should I be looking for in determining the cause of the double fault? A few more details. This only happens at boot time and is 100% reproducible at the same location every time. ...Duane ps Sorry, I can't post the actual back trace due to license restrictions (please draw your own conclusions. :-) _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: Run daemon from installer as root
by Rakesh Singhal 06 Apr '09

06 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:date:message-id:subject :from:to:content-type; bh=nAkh/FVbgVg/eJ3TcMTnEEeclZ2G0dkgX9erfhvVuuo=; b=MitDGyb4rilMUWM2coI3/rF5/z3uHAeNEOiCtb3SsiqkaxBLHExmuqAyFn0axIbcyr 70I1vxvkKUUN/IGyjd6AJLDgYQ3CoYs3bAhJ/WKX+cl2V/9ZfCKNE0ehlJ23Mc94joUr FsqcAqc+gXV7DJgfdt8V9GIDZPtpyxZKkUXw8= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=kDveNTnAC+GdxnvWZlbTcm1ZF2K6OycEJeqb6SB8lNiRtOpNNSTld1AJjGOXTMh7dJ +n3huzA5N49f2tfpp/3zpnkf2BeYcViPD5JkfpI6B4OIdpza+Z3brrItAB6Fwfk2YN5+ fVVbvstmh2Bg9QXrzf3Nqgx9IRYo2KHy8FgRk= --- At Sun, 5 Apr 2009 20:03:42 +0530, Rakesh Singhal wrote: Hi all, This is not a limitation of the installer. This is a limitation of the sh (and perl). Well, not really a limitation, it's a security feature. Some script interpreters will refuse to run a script as root as a security precaution. I don't recall the exact details about when this choice is made or how to overcome it. My choice for overcoming the problem was to choose a different interpreter (python). I suppose it's just a matter of time before that door is closed also. I'd like to know what the alternatives are so that scripts within an installer can be run with Administrator/root privileges. Just in case, a simple solution is probably to: 1) Be sure that the installer requires an admon/root authentication. 2) Use sudo to call launchctl even from the shell script. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com I have created an installer for my daemon application. I want my daemon to run as root after installation. Before installation I used to run daemon using "sudo launchctl load /Library/LaunchDaemons/ com.mycompany.mydaemon.plist". In installer I tried using run command or run script but it works only in 10.4.11 ppc but not with 10.5.4 intel. I want to set some file permissions/ownerships also but it doesnt work. Installer can be run only from admin users. Is there anyway to run daemon as root using command or script?

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Re: Are kqueue events "round robin"?
by Påhl Melin 06 Apr '09

06 Apr '09

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type :content-transfer-encoding; bh=QOeQ7am4wNTGStQrM31YtMkPhPQLuXenbUW2EW7s5Rg=; b=R56Y2nIAH/MgInOfxqTZtUAbyQYG5tlWwh+4a0iaYge+6mvUs77SYqssuBU534SQEd Ia/HbyWuUHUUYUpmtWVn8pXwGjA+8My3eUy/E4l4MRsnzb5LNtKimL0LiAr+wecfUot0 7mb62Q3lG1obYxfwE0F9NU+vHxGurGMjUPYWk= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type:content-transfer-encoding; b=ixmyp8Y4O9jgSpqHTquLel5TXI+7ay3DTG7wAOJ33VyO92r7YpX4703zm8voBh8kyy rAmhLd8RJoFQf8h5jGLoRAO2CZbhy/3lbLRI3fmXO5lWHaYV/UKSIOxFH+5MsZBYX9lz 5O4AQlFyPbJ53bU1rkyoUUuPVv3FkOLW7U/38= 2009/4/2 A.M. <agentm(a)themactionfaction.com>: > On Apr 2, 2009, at 11:07 AM, Påhl Melin wrote: >> Hi all, >> >> I have a question regarding the order events are returned from a >> kevent() call on a kqueue, if I only supply one event in the event >> list and no events are changed? Is there a predefined order in which >> the filters are processed and returned as events when there are >> multiple events available at the same time? >> >> For example if I have two filters, one EVFILT_READ filter and one >> EVFILT_WRITE filter and there is available room in both the read and >> the write buffers. If I make four subsequent calls, in what order will >> the events be returned? Will I get EVFILT_READ, EVFILT_WRITE, >> EVFILT_READ, EVFILT_WRITE? Or will I e.g. get one of the events >> repeatedly until that buffer is empty/full, like EVFILT_READ until I >> have read everything in the read buffer? Or is random or some other >> algorithm? >> >> What I want to do is to alternate between read and write events to get >> good responsiveness. I suppose I could change the events in the kqueue >> but it would be easier to rely on some guaranteed behavior. > > The order you receive is the order that the kernel put the events in the > queue- that is, after all, what makes it a k*queue*. If this is socket > communications, you will get spammed with EVFILT_WRITE events as long as the > socket buffer is full; however, this does not imply that you will get no > read events in between. But you should selectively enable and disable > EVFILT_WRITE events based on whether or not you actually have stuffed the > socket buffer (when the non-blocking socket I/O returns fewer bytes than > what you passed in). I'm writing a messaging framework that sends asynchronous messages between processes on a local machine using Unix Domain Sockets and between machines using normal TCP/IP sockets. My idea was to use a design where I keep an open socket between two nodes and have one "service" thread handling the communication on the socket using a kqueue and looping around a kevent() call. When there are outgoing commands present, the thread enables the EVFILT_WRITE filter and waits for available space in the write buffer. When all commands are written to the socket, the EVFILT_WRITE filter is disabled. At the same time I also would have a EVFILT_READ enabled, receiving incoming replies for the commands and also asynchronous incoming messages. In a very simplified form without error checking, my loop would look like this: for (;;) { numberOfEvents = kevent(kq, NULL, 0, &event, 1, NUL); if (event.filter == EVFILT_READ) { // handle read events } else if (event.filter == EVFILT_WRITE) { // handle write events } } In the read and write event handling I would read or write a few bytes for the current command and I would then continue the loop waiting in the kevent() statement again. When I have multiple commands and replies I assume that the kevent() would return immediately with the data member containing the remaining bytes to be read (or space left in the write buffer). I would expect the kqueue not to be filled up with EVFILT_READ and EVFILT_WRITE events, but to have only one of each whenever the buffers are "ready". But the question is if I'm guaranteed to have alternating read and write events? Or if I get starvation of any kind? I don't see anything about this matter in the man pages so I'm curious if it's specified at all? > I haven't experienced any event starvation situation, but in case you have, > the best approach would be to implement an array over kqueue. Simply read > more than one event into your own queue and you can algortithmically decide > which events to process (and then remove them from the array- obviously it's > no longer a queue). But don't waste time implementing this approach unless > you are indeed experiencing starvation. Thanks, I hadn't really considered returning multiple events and make my own decision. But it would of course be easier if a reasonable decision was already made by the kevent() call. > Since one thread can only do so much, if you have lots of socket or sources, > then you may want to break their processing into separate thread (kqueue is > thread-safe and works well across multiple threads). Even a single socket > read and write events could be broken out across threads. That's interesting. I what sense is kqueue thread safe? Can I wait on the same kqueue in two different threads, each calling kevent() or do I make two kqueue:s, one with a read filter and the other queue with a write event on the same socket descriptor? > Cheers, > M _______________________________________________ Do not post admin requests to the list. They will be ignored. 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Re: Run daemon from installer as root
by Rakesh Singhal 06 Apr '09

06 Apr '09

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