I agree, unless I use setjmp/longjmp for that. Besides error recovery, there are occasionally other times when we want to locally "return" to a common state and start "from the top" again. I find such uses very clear in their intent, and if commented well, not hard to follow at all - as long as there is not more than one "top" :) On 03/09/2023 04:21 PM, Warner Losh wrote:

Oh also sometimes for breaking out of multiple levels of while/for loops. The alternatives are often worse. Warner On Thu, Mar 9, 2023, 4:31 PM Luther Johnson <luther(a)makerlisp.com> wrote:

On Thu, Mar 9, 2023, 5:55 PM segaloco <segaloco(a)protonmail.com> wrote: Yea. I recall a proposal to add break label; and the label could only be at the end of a loop. The objection was why bloat the compiler with another goto... I developed my restricted lack of fear after a stint in Java with its multilevel break... Warner Now doing some research, more languages support GOTO than I thought,

Ralph Corderoy <ralph(a)inputplus.co.uk> wrote: C predates the Bourne shell by several years. Remember too that the C compiler had to fit in a small space; having multilevel or labelled breaks requires more bookkeeping. The idea of labelled loops is not at all new, Ada had them in the 80s and it wasn't new then. IIRC Go also provides them. Arnold

Ralph Corderoy <ralph(a)inputplus.co.uk> wrote: Yes, since you have to keep track of a label in a table somewhere that you can look up. Is it *that* much more that the PDP-11 C compiler could not have handled it? I don't know. Arnold

Ralph Corderoy <ralph(a)inputplus.co.uk> wrote: Those would undoubtedly be easier. I asssume a "stack the address" sort of implementation a la BWK's ratfor, but I could be wrong, as I'm not familiar with the PDP-11 C compiler. Arnold

Dave Horsfall wrote in &lt;alpine.BSF.2.21.9999.2303101657460.4881(a)aneurin.horsfall.org&gt;: |On Thu, 9 Mar 2023, Warner Losh wrote: |> In C I use it all the time to do goto err for common error recovery |> because C doesn't have anything better. | |<AOL> |Me too :-) |</AOL> | |Seriously, I also use setjmp()/longjmp() for a more elegant exit from a That is sheer unbelievable, really? _So_ expensive! |deeply-nested loop; "break N" to break out of "N" loops, anyone? I |haven't found that yet... Very often i find myself needing a restart necessity, so "continue N" would that be. Then again when "N" is a number instead of a label this is a (let alone maintainance) mess but for shortest code paths. All the "replacements", like closures, plain inner functions, even more contorted conditionals (i think in the last seven days i saw at least three fixes fly by due to logic errors in contorted conditionals, tiny C compiler, OpenBSD i think bpf/bgpd?, and some FreeBSD commit, which sums up as "Pascal: no"), and "state machine indicating variables" are not as elegant and cheap, and do not allow an as human-receivable control flow (imho), as a simple jump can be. Like my always quoted exampe that adds unnecessary conditionals which evaluate over and over again for nothing if(defined($nl = $self->begin_line)){ $self->begin_line(undef); $self->seen_endl(1); $ogoditisanewperl = 1 #goto jumpin; } while($ogoditisanewperl || ($nl = readline $self->infh)){ if(!$ogoditisanewperl){ ++${$self->__lineno}; $self->seen_endl($nl =~ s/(.*?)\s+$/$1/) } $ogoditisanewperl = 0; #jumpin: |Of course, in those days it was setexit() etc :-) ENTRY(setexit, 0) movab setsav,r0 movq r6,(r0)+ movq r8,(r0)+ movq r10,(r0)+ movq 8(fp),(r0)+ # ap, fp movab 4(ap),(r0)+ # sp movl 16(fp),(r0) # pc clrl r0 ret ENTRY(reset, 0) movl 4(ap),r0 # returned value movab setsav,r1 movq (r1)+,r6 movq (r1)+,r8 movq (r1)+,r10 movq (r1)+,r12 movl (r1)+,sp jmp *(r1) setsav: .space 10*4 .text Cheap it is not. But maybe cheaper than calling a closure or inner function with all the (repeated) stack setup and unwinding. |-- Dave --End of &lt;alpine.BSF.2.21.9999.2303101657460.4881(a)aneurin.horsfall.org&gt; --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)

On Fri, 10 Mar 2023, Steffen Nurpmeso wrote: How often would you call setjmp()/longjmp()? -- Dave

Warner Losh wrote in &lt;CANCZdfqOZ3wrHktZGk3BrHV5ZdbkDyRPGxH61Mq87TVDQRQh7A(a)mail.gmail.com&gt;: |On Sun, Mar 12, 2023, 2:47 PM Dave Horsfall &lt;dave(a)horsfall.org&gt; wrote: |> On Fri, 10 Mar 2023, Steffen Nurpmeso wrote: |> |>>|Seriously, I also use setjmp()/longjmp() for a more elegant exit from a |>> |>> That is sheer unbelievable, really? _So_ expensive! |> |> How often would you call setjmp()/longjmp() Only on a Sunday! I never used these myself of free will. (And never regulary at all until i took maintainership of a BSD Mail clone, which is the examplary piece of software to show that BSD signal handling and SA_RESTART are a terrible misconception, especially as soon as the software gets larger. .. In my opinion. Once it was able to run "24/6" i counted the number of system calls necessary for signal block / release and installation / removal over a week, and i think the number was way in the six digits. System calls them all! I should have taken the OpenBSD variant instead, and simply take over what "was good", and it would be much, much better by now. They did the work and reduced the very messy part to two exactly locatable system call points of interest. (I looked i guess 2014-<2017.) A very bad decision. But if i live long enough i will make it, and another one i would really long for.) |Cheap enough for occasional error handling, way too expensive for a generic |exception handling system... processors with lots of registers were more of |a problem... Even on a x86(-32) i have gnashed with my teeth. And that with a Cyrix from 1996 .. and not to think about i386 or even earlier processors with so few memory and speed. I remember _for sure_ looking at the jmpbuf structure by then, and the assembler files (sheer magic by then) and x86 instructions. "Some" jpeg library used jump buffers to signal errors. (I got rid of most sources for things that will never come true, but i do have libjpeg-turbo ball due to package dependencies, and they also use that internally, but looking at it it seems to be a different thing.) That is maybe ok since image processing is maybe expensive enough by itself to simply say they do not care about proper error paths along the way but take a "dead-end exit". (But it was i think not like that with the jpeg i have in mind.) --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)

Dave Horsfall wrote in &lt;alpine.BSF.2.21.9999.2303131331350.67613(a)aneurin.horsfall.org&gt;: |[ Followups to COFF, as this is rapidly becoming a Unix tutorial ] .. |On Sun, 12 Mar 2023, Steffen Nurpmeso wrote: ... |> Even on a x86(-32) i have gnashed with my teeth. And that with ... |You can read X86 assembler? I can only do that after a few stiff Unfortunately i stopped my ambitions (nasm was non-portable but fun). I never stepped to ARM, i hate that, i read according Net and FreeBSD commits with lots of interest. Many years ago there was a thrilling commit series for string and memory ops on NetBSD that i sometimes still speak of ... Matt Thomas i think it was. ("Thrilling" it was for me; by then.) |drinks... I did buy the book (in order to debug a floating bug defect |in the optimiser -- hey, let's optimise this instruction right out! -- and But floating-point i run away. |I've never trusted optimisers since). | |[*] |Cue the saying about it being impossible to design a foolproof system. | |-- Dave, the iconoclast "Dawn Of The Iconoclast"; Lisa Gerrard is also an Aussie and nuclear she is, isn't she. (Shown with unforgotten Klaus Schulze at the Loreley -- since most of the UNIX beards are surely some kind of long haired beauties this could even go to TUHS.) Yeah, signals, no. Problems anywhere. But i have a command PKILL_TMUX "pkill -CONT tmux" in my ~/.cwmrc (when Linux sends ^Z to the wrong for whatever reason), and enough ptys to go to when ogg123 again gets an interruption wrong and hangs deadly, only killable via -KILL. I think setting a flag plus EINTR is a way, but ERESTART is not handable if you sit on something blocking but have to act upon the signal; message passing -- if you do have an event loop based program then this is nice; then again i woke up with horrors for the (first) Linux thread library (i have looked in) over twenty years ago, and they used a worker and serialization via such as a regular thing; also owed to Butenhof's POSIX thread design of course, which is too "free" in my eyes (i'd rather have a dedicated main thread plus workers); just like C++ exceptions (i saw software which "throws char*"). --End of &lt;alpine.BSF.2.21.9999.2303131331350.67613(a)aneurin.horsfall.org&gt; --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)