Beefy Boxes and Bandwidth Generously Provided by pair Networks
Pathologically Eclectic Rubbish Lister
 
PerlMonks  

Re^5: The implementation of SIGHUP in Win32 Perl

by bulk88 (Priest)
on Sep 04, 2013 at 19:43 UTC ( #1052428=note: print w/ replies, xml ) Need Help??


in reply to Re^4: The implementation of SIGHUP in Win32 Perl
in thread The implementation of SIGHUP in Win32 Perl

The problem with just "sending" a message to the main thread is, what if the main thread is in a blocking syscall, directly from Perl lang or through some XS-ed C library? How do you ensure the responsiveness of the fake-signal if the main thread is blocked in the kernel?

I did once take a C debugger, when the console event hit the 2nd thread, I paused the main thread, let the 2nd thread run to completion and shut down Perl interp struct, and I dont remember (and cant research it ATM, normally I would research it for you but im not at my devel machine this post is from memory), but I think the 2nd thread ended the 2nd thread, I then ran the 1st main thread, now with an almost uninitialized interp struct, and it very quickly called C's exit() and that was it. I also fixed a race condition maybe a year ago between sending a kill 9 from a parent fork thread/fake process to the child fork thread/fake process, where the child thread was still initializing itself in user mode kernel32/ntdll, before calling any process specific code, and when killing the child thread, it would leave the DLL loader lock, locked, by the now gone 2nd thread, when the perl interp trys to exit, the DLL loader from the main thread tried to aquire the DLL loader lock and hung forever.

I've also dispatched events from multi threaded pure C code, using Perl's win32 fake signals dispatch code by setting a 1 in some array in the perl interp struct which corresponds to one of the 2 dozen signals names on Win32 perl, then setting a global flag that there is a pending signal for the interp to dispatch to the perl lang level, and on PERL_ASYNC_CHECK() the fake signal was dispatched, which eventually called a Perl lang sig handler which then called XS code which pulled events off the pure C's event queue. I think I used signal NUM05.

You should ask on the p5p mailing list. You will get more C/interp internal knowledgeable eyes than on PerlMonks. The p5p IRC room has less eyes and less Win32 eyes. Since there arent very many p5p win32 guys. You probably want an answer from steve hay, tony cook, or jan dubois. None of them are active at PM. Also use git blame, for example http://perl5.git.perl.org/perl.git/blame/HEAD:/win32/win32.c and look at the evolution of the code you are wondering about.


Comment on Re^5: The implementation of SIGHUP in Win32 Perl
Re^6: The implementation of SIGHUP in Win32 Perl
by klaten (Novice) on Sep 05, 2013 at 17:27 UTC

    Wow, that's *seriously* deep stuff, you've attempted! I don't think I want to go that deeply into the forest. The quote, "Do not meddle in the affairs of dragons, for you are crunchy and taste good with ketchup" would seem to apply to me regarding the things you tried. Your paragraph beginning with "I did once take a C debugger, . . .," made me smile because it sounded like the beginning of one of the stories an Arthurian knight might have spun. Powerful stuff, nonetheless.

    The next paragraph about the dispatch of events from perked my interest because I can see how that could work to solve the issues you raised in the first paragraph. I'm going to return to that first paragraph because I think it's the most interesting of all.

    Thank you for the advice about the p5p mailing list. I've come to the conclusion that I need to craft my own console control handler in XS and install it on top of Perl's, ensure that it works to my satisfaction, and then I'll be able to make a more acceptable contribution. It sounds like they may be a great source of wisdom in that endeavor. And tracking the evolution of win32.c actually sounds like fun! So I know I'll do that. Thank you, again.

    Now back to that first paragraph (written with a smile)! You wrote:

    How do you ensure the responsiveness of the fake-signal if the main thread is blocked in the kernel?

    One possible answer might be, "you don't." Your other question holds the key to that idea.

    The problem with just "sending" a message to the main thread is, what if the main thread is in a blocking syscall, directly from Perl lang or through some XS-ed C library?

    Isn't Perl5 evolving in that direction, anyway? Aren't those restrictions similar to the limitations of "safe signals"? Are there many things that can *only* be done via blocking syscalls in the main process? It reminds me of the classic "doctor-patient joke:"

    Doctor: Please tell me about your problem.
    Patient: It hurts when I do this.
    Doctor: So don't do that!

    In Perl5 we have many tools to allow the use of multiple processes (in Windows, Linux, and the other platforms as well) to handle the types of things most people would want to use blocking syscalls for anyway. With simple IPC techniques like piped opens and "safe signals" why bother with complex, flawed, and potentially crash prone things like full POSIX signals anyway? I can see that you have the skills and moxie to attack that problem, but I can't help but wonder whether or not the better way is simply to accept Perl5 as a wonderful single-threaded C program (perhaps the greatest, ever) and maybe leave those more complex issues to the Perl6 people.

      Now back to that first paragraph (written with a smile)! You wrote:

      How do you ensure the responsiveness of the fake-signal if the main thread is blocked in the kernel?

      One possible answer might be, "you don't." Your other question holds the key to that idea.

      Then you dont have "signals" at all. die "signals not implemented";
      The problem with just "sending" a message to the main thread is, what if the main thread is in a blocking syscall, directly from Perl lang or through some XS-ed C library?

      Isn't Perl5 evolving in that direction, anyway? Aren't those restrictions similar to the limitations of "safe signals"? Are there many things that can *only* be done via blocking syscalls in the main process?

      Evolving? IMO Perl 5 doesn't evolve. Many people with decision making power see Perl 5 as being in "maintenance mode" for legacy code, and back-compat is above all else.

      What are safe signals? That is a term that Perl 5 created to mean a queue and deferred execution of signals at safe points. It isn't an OS feature. Non-blocking and async IO support in the core language is hit or miss on all the different platforms that Perl runs on. On Win32 Perl, sockets are the only non-synchronous IO. I've never seen any evidence of anyone using the native Win32 API (XS) in Perl for non-synchronous IO except me. The XS code for GUI toolkits on Perl sometimes disable (Glib) with a comment in the code saying to use "native" Perl IO instead. In other cases the toolkits (QT) do blocking IO in an fresh OS thread, which is incompatible with Perl's architecture since OS specific non-syncronous IO is so hit or miss that the toolkit authors gave on it. Or, its not implemented in the toolkit on windows, Perl Tk. Or not implemented at all, (WX).

      In Perl5 we have many tools to allow the use of multiple processes (in Windows, Linux, and the other platforms as well) to handle the types of things most people would want to use blocking syscalls for anyway. With simple IPC techniques like piped opens and "safe signals" why bother with complex, flawed, and potentially crash prone things like full POSIX signals anyway? I can see that you have the skills and moxie to attack that problem, but I can't help but wonder whether or not the better way is simply to accept Perl5 as a wonderful single-threaded C program (perhaps the greatest, ever) and maybe leave those more complex issues to the Perl6 people.

      Perl 6 is not Perl 5, and never claimed to be syntax compatible. Is C# the successor of C++? Your piped open will block on windows when there is no data from the child process in the pipe.

        Thank you so much for taking the time of day with me. Your posts are entertaining and enlightening. You wrote "I break dragons every day, they are much better for transporation than horses," that really made me smile, you really are quite the "code warrior." You also wrote, "if you haven't figured it out yet, I'm a p5per." That explains the scorch marks on your dragon shield (smiling). Thank you. Folks like you keep Perl5 fun for folks like me.

        I think we have some philosophical differences about Perl5 and that's fine, it's part of what makes life so interesting. I'm (like many folks these days) "financially distressed" (smiling), I mention that because I think it has changed the way I think of many things including Perl5. When you're poor, but resourceful (I like to think of myself that way), you look at individual things around you and see, not its age and specks of rust, but instead, its utility. Perl5 is still the "Swiss army chainsaw" to me. I expect there will be scant few problems in this life I can't solve with Perl and C (world peace, anyone).

        Much of the Perl5 community seems dispirited these days. I read comments similar to "many people with decision making power see Perl 5 as being in "maintenance mode" for legacy code, and back-compat is above all else," in a lot of places and it seems tinged with regret. Well, I certainly don't have any "decision making power," but I like the idea of Perl5 being in "maintenance mode." You could probably say the same thing of the "C" language; wouldn't it be cool if Perl5 because the dynamic language equivalent of "C"?

        When I wrote:

        With simple IPC techniques like piped opens and "safe signals" why bother with complex, flawed, and potentially crash prone things like full POSIX signals anyway?

        and

        Are there many things that can *only* be done via blocking syscalls in the main process?

        You replied:

        What are safe signals? That is a term that Perl 5 created to mean a queue and deferred execution of signals at safe points. It isn't an OS feature. Non-blocking and async IO support in the core language is hit or miss on all the different platforms that Perl runs on.

        and

        Your piped open will block on windows when there is no data from the child process in the pipe.

        Sure, I get that. But, now that I have these "fakey," "pseudo," "signal-message hybrid things" in my toolbox, I could:

        1. Send a signal from child to parent to indicate I have a line to read,
        2. Read the line in the parent,
        3. Send a signal from parent to child to say "got it, send me another."

        Goodbye blocking, hello crude but effective flow control. I love TIMTOWTDI, problems usually reduce themselves down to finding the "appropriate" technique to apply.

        One of my favorite Perl books is Mastering Perl/Tk because they took the shortcomings of Win32 and found workarounds. No fileevent? No problem, let's try memory-mapped files, instead. Cool! I wish the Perl community would stop feeling sorry for itself, embrace TIMTOWTDI enthusiastically, and help us "pikers" use some of these more obscure "attachments" to the "chainsaw" to cut through our own problems. But come to think of it, that's what PerlMonks is, isn't it? I have no Python/Ruby envy at all, they'll have to pry Perl5 from my "cold, dead, hands"! Cheer up, everybody. Perl5 is still great!

        One of the craziest things to me about modern society is the notion of "obsolescence." I find it insane that folks toss away perfectly good smartphones simply because they can't talk to Siri. Well, Perl5 may not be able to talk to Siri (yet!), but it can do just about anything else most of us "mere mortals" need to do. Please keep slaying dragons, there are plenty of us who happen to like living in this "village" and need folks like you to keep us safe there.

        I've never seen any evidence of anyone using the native Win32 API (XS) in Perl for non-synchronous IO except me.

        Where can I see that?

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1052428]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others making s'mores by the fire in the courtyard of the Monastery: (13)
As of 2014-07-11 18:38 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    When choosing user names for websites, I prefer to use:








    Results (235 votes), past polls