Re: Alarm signal and recv system call
Matthew Fluet <[email protected]> Thu, 15 Nov 2018 16:57:32 -0500
| Newsgroups | gmane.comp.lang.ml.mlton.user |
|---|---|
| Message-ID | <CAMrhFL73+gAMX_FX_QL-xQWRt5W6PwSWtANOTN+jwJbVRX+euQ@mail.gmail.com> |
--===============7241781668761474021== Content-Type: multipart/alternative; boundary="000000000000ed09d2057abb2320" --000000000000ed09d2057abb2320 Content-Type: text/plain; charset="UTF-8" In addition to Henry's comments, there is a little more to the story. It is true that at the libc level, an interrupted system call will typically return immediately with -1 and errno set to EINTR. MLton's implementation of the Basis Library chooses to restart most such libc functions. However, this is configurable via `val MLton.Signal.restart : bool ref`. See the "Interruptible System Calls" section of http://mlton.org/MLtonSignal. The default (of restarting system calls) makes sense for some uses of signals (e.g., profiling or asking a long-running program to save state in response to a periodic signal). Also, in the context of high-level operations, performing something like BinIO.output with a very large output vector could result in multiple system calls (as buffers are filled), so it may be almost impossible to handle the OS.SysError exception and resume so that no output is lost. On Thu, Nov 15, 2018 at 11:32 AM Henry Cejtin <[email protected]> wrote: > You have to remember that MLton signal handlers are running in a > separate thread. It gets passed the thread that was interrupted and > returns the thread to run when the handler is finished. The result of > Handler.simple returns the thread it was called with, and hence restarts > the interrupted thread. > > If you want the Socket.recvVec (or whatever) to be `aborted', then you > can't use Handler.simple to make the handler. Instead you have to have > some other thread to resume, or, if you want the program to terminate, > you have to terminate it in the handler. You can do the latter with, > for example, OS.Process.exit. > > Doing this, your sample program would look like this: > > fun h = let val () = print "Alarm sig\n" > in OS.Process.exit OS.Process.failure > end > val () = MLton.Signal.setHandler (Posix.Signal.arm, > MLton.Signal.Handler.simple h) > val () = Posix.Process.Alarm (Time.fromSeconds (Int.toLarge 3)) > val r = Socket.recvVec (socket, 1024) > val () = print "Done\n" > On Thu, Nov 15, 2018 at 5:54 AM Kostirya <[email protected]> wrote: > > > > I was surprised to find that Alarm signal do not abort recvVec function. > > How is this possible? > > I thought recv was always aborted on signal. > > > > > > I use for test: > > > > val _ = MLton.Signal.setHandler(Posix.Signal.alrm, > > MLton.Signal.Handler.simple (fn _ => print "Alarm sig\n")) > > val _ = Posix.Process.alarm (Time.fromSeconds (Int.toLarge 3)) > > val r = Socket.recvVec (socket, 1024) > > val _ = print "Done\n" > > > > -- > > You received this message because you are subscribed to the Google > Groups "MLton-user" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to [email protected]. > > > > > > > > _______________________________________________ > > MLton-user mailing list > > [email protected]; [email protected] > > https://lists.sourceforge.net/lists/listinfo/mlton-user > > -- > You received this message because you are subscribed to the Google Groups > "MLton-user" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > > > > _______________________________________________ > MLton-user mailing list > [email protected]; [email protected] > https://lists.sourceforge.net/lists/listinfo/mlton-user > -- You received this message because you are subscribed to the Google Groups "MLton-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. --000000000000ed09d2057abb2320 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div dir=3D"ltr"><div class=3D"gmail_default" style=3D"fon= t-family:"courier new",monospace;font-size:large">In addition to = Henry's comments, there is a little more to the story.=C2=A0 It is true= that at the libc level, an interrupted system call will typically return i= mmediately with -1 and errno set to EINTR.=C2=A0 MLton's implementation= of the Basis Library chooses to restart most such libc functions.=C2=A0 Ho= wever, this is configurable via `val MLton.Signal.restart : bool ref`.=C2= =A0 See the "Interruptible System Calls" section of=C2=A0<a href= =3D"http://mlton.org/MLtonSignal">http://mlton.org/MLtonSignal</a>.=C2=A0 T= he default (of restarting system calls) makes sense for some uses of signal= s (e.g., profiling or asking a long-running program to save state in respon= se to a periodic signal).=C2=A0 Also, in the context of high-level operatio= ns, performing something like BinIO.output with a very large output vector = could result in multiple system calls (as buffers are filled), so it may be= almost impossible to handle the OS.SysError exception and resume so that n= o output is lost.</div><br><div class=3D"gmail_quote"><div dir=3D"ltr">On T= hu, Nov 15, 2018 at 11:32 AM Henry Cejtin <<a href=3D"mailto:henry.cejti= [email protected]">[email protected]</a>> wrote:<br></div><blockquote cla= ss=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid = rgb(204,204,204);padding-left:1ex">You=C2=A0 have=C2=A0 to=C2=A0 remember= =C2=A0 that=C2=A0 MLton=C2=A0 signal=C2=A0 handlers=C2=A0 are running in a<= br> separate thread.=C2=A0 It gets passed the thread=C2=A0 that=C2=A0 was=C2=A0= interrupted=C2=A0 and<br> returns=C2=A0 the=C2=A0 thread to run when the handler is finished.=C2=A0 T= he result of<br> Handler.simple returns the thread it was called with, and hence restarts<br= > the interrupted thread.<br> <br> If=C2=A0 you=C2=A0 want the Socket.recvVec (or whatever) to be `aborted'= ;, then you<br> can't use Handler.simple to make the handler.=C2=A0 Instead you have to= =C2=A0 have<br> some=C2=A0 other=C2=A0 thread to resume, or, if you want the program to ter= minate,<br> you have to terminate it in the handler.=C2=A0 You can do=C2=A0 the=C2=A0 l= atter=C2=A0 with,<br> for example, OS.Process.exit.<br> <br> Doing this, your sample program would look like this:<br> <br> =C2=A0 =C2=A0 fun h =3D let val () =3D print "Alarm sig\n"<br> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 in OS.Process.exit OS.Process.fai= lure<br> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 end<br> =C2=A0 =C2=A0 val () =3D MLton.Signal.setHandler (Posix.Signal.arm,<br> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 MLton.Signal.Ha= ndler.simple h)<br> =C2=A0 =C2=A0 val () =3D Posix.Process.Alarm (Time.fromSeconds (Int.toLarge= 3))<br> =C2=A0 =C2=A0 val r =3D Socket.recvVec (socket, 1024)<br> =C2=A0 =C2=A0 val () =3D print "Done\n"<br> On Thu, Nov 15, 2018 at 5:54 AM Kostirya <<a href=3D"mailto:kostirya@gma= il.com" target=3D"_blank">[email protected]</a>> wrote:<br> ><br> > I was surprised to find that Alarm signal do not abort recvVec functio= n.<br> > How is this possible?<br> > I thought recv was always aborted on signal.<br> ><br> ><br> > I use for test:<br> ><br> > val _ =3D MLton.Signal.setHandler(Posix.Signal.alrm,<br> > MLton.Signal.Handler.simple (fn _ =3D> print "Alarm sig\n"= ;))<br> > val _ =3D Posix.Process.alarm (Time.fromSeconds (Int.toLarge 3))<br> > val r =3D Socket.recvVec (socket, 1024)<br> > val _ =3D print "Done\n"<br> ><br> > --<br> > You received this message because you are subscribed to the Google Gro= ups "MLton-user" group.<br> > To unsubscribe from this group and stop receiving emails from it, send= an email to <a href=3D"mailto:mlton-user%[email protected]" target= =3D"_blank">[email protected]</a>.<br> ><br> ><br> ><br> > _______________________________________________<br> > MLton-user mailing list<br> > <a href=3D"mailto:[email protected]" target=3D"_blank">= [email protected]</a>; <a href=3D"mailto:[email protected]= g" target=3D"_blank">[email protected]</a><br> > <a href=3D"https://lists.sourceforge.net/lists/listinfo/mlton-user" re= l=3D"noreferrer" target=3D"_blank">https://lists.sourceforge.net/lists/list= info/mlton-user</a><br> <br> -- <br> You received this message because you are subscribed to the Google Groups &= quot;MLton-user" group.<br> To unsubscribe from this group and stop receiving emails from it, send an e= mail to <a href=3D"mailto:mlton-user%[email protected]" target=3D"_bl= ank">[email protected]</a>.<br> <br> <br> <br> _______________________________________________<br> MLton-user mailing list<br> <a href=3D"mailto:[email protected]" target=3D"_blank">MLton= [email protected]</a>; <a href=3D"mailto:[email protected]" ta= rget=3D"_blank">[email protected]</a><br> <a href=3D"https://lists.sourceforge.net/lists/listinfo/mlton-user" rel=3D"= noreferrer" target=3D"_blank">https://lists.sourceforge.net/lists/listinfo/= mlton-user</a><br> </blockquote></div></div></div> <p></p> -- <br /> You received this message because you are subscribed to the Google Groups &= quot;MLton-user" group.<br /> To unsubscribe from this group and stop receiving emails from it, send an e= mail to <a href=3D"mailto:[email protected]">mlton-user+unsu= [email protected]</a>.<br /> --000000000000ed09d2057abb2320-- --===============7241781668761474021== Content-Type: text/plain; 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