Or You Could Simplify The Error-Recovery Paths

Posted Dec 25, 2014 21:34 UTC (Thu) by cesarb (subscriber, #6266)
In reply to: Or You Could Simplify The Error-Recovery Paths by ldo
Parent article: The "too small to fail" memory-allocation rule

> do {
> if (failure)
> break;
> } while (false);

Wouldn't it be simpler and more readable to use a goto instead of a pseudo-loop?

(The Linux kernel does use the "set pointers to NULL and on error free them if they are not NULL" paradigm, of course using a "goto error" instead of a pseudo-loop, but the error-recovery paths being discussed are not merely "freeing locally allocated memory"; they can also have things like "unlocking a mutex" or "updating the filesystem block allocation structures to mark as free the blocks which had been reserved for this task".)

to post comments

Re: Wouldn't it be simpler and more readable to use a goto instead of a pseudo-loop?

Posted Dec 25, 2014 22:08 UTC (Thu) by ldo (guest, #40946) [Link] (65 responses)

No! No GOTOs. They don’t nest easily, and they lead to spaghetti code. Look at the example code I linked above, and think how it would look with GOTOs all over the place. Avoid GOTOs!

Re: Wouldn't it be simpler and more readable to use a goto instead of a pseudo-loop?

Posted Dec 25, 2014 22:23 UTC (Thu) by mchapman (subscriber, #66589) [Link] (27 responses)

> Look at the example code I linked above, and think how it would look with GOTOs all over the place.

There would be precisely as many "goto" statements as you have "break" statements. It's much of a muchness, in my opinion.

Re: There would be precisely as many "goto" statements

Posted Dec 25, 2014 23:07 UTC (Thu) by ldo (guest, #40946) [Link] (26 responses)

And you would need a different label for each. And the extra visual burden of ensuring that each goto is paired with the right label. Which is unnecessary with a break, since that can only ever terminate one enclosing construct.

And the further burden of getting things wrong when you try refactoring the code.

Like I said: NO GOTOs!

Re: There would be precisely as many "goto" statements

Posted Dec 26, 2014 0:01 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (5 responses)

Except that NOW you have an extra burden to check that break actually breaks out of a right loop.

So, YES to gotos for error handling!

Re: So, YES to gotos for error handling!

Posted Dec 26, 2014 0:37 UTC (Fri) by ldo (guest, #40946) [Link]

Put your money where your mouth is. You have my code; go rewrite it!

Re: There would be precisely as many "goto" statements

Posted Dec 26, 2014 7:38 UTC (Fri) by epa (subscriber, #39769) [Link] (3 responses)

Perl allows 'last' (its equivalent of 'break') to take a loop label. That would be a useful enhancement to C.

Re: There would be precisely as many "goto" statements

Posted Dec 26, 2014 7:43 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link]

That's a different issue - exit from multiple nested loops. In languages lacking labeled loops (C, C++) it's often a place where 'goto' is used.

Re: There would be precisely as many "goto" statements

Posted Jan 16, 2015 5:10 UTC (Fri) by CameronNemo (guest, #94700) [Link]

Rust got that recently. It is interesting, but a little strange/complicated.

Re: There would be precisely as many "goto" statements

Posted Jan 16, 2015 18:23 UTC (Fri) by zlynx (guest, #2285) [Link]

Whenever I got to wanting labeled blocks in C, I sat down (OK,really I was already sitting down) and decided to add another function instead.

That almost always made the code cleaner, and let me exit the block (which was now a function) with a simple "return."

Re: There would be precisely as many "goto" statements

Posted Dec 26, 2014 7:34 UTC (Fri) by WolfWings (subscriber, #56790) [Link] (19 responses)

Um... since when?

if (error1) {
  goto label;
}

/* ... more code ... */

if (error2) {
  goto label;
}

/* ... more code ... */

label: free(pointer);

You can use a single label for any number of goto's, so each label is specifically describing it's use case (freeAndExit perhaps, or whatever semantic name you want to give it) and there's no more/less lines than your do{}while(false); construct but copy-pasting code inside/outside the strcture can't break it as easily.

Just saying you're wrong about the claim of needing a billion labels, goto is many-to-one not one-to-one in that regard.

Re: you're wrong about the claim of needing a billion labels

Posted Dec 26, 2014 21:15 UTC (Fri) by ldo (guest, #40946) [Link] (17 responses)

Fine. Try reworking the example I gave above, then. That has allocations nested up to three levels deep, as well as loops. See how well that works using GOTOs.

Re: you're wrong about the claim of needing a billion labels

Posted Dec 27, 2014 0:47 UTC (Sat) by reubenhwk (guest, #75803) [Link] (7 responses)

GOTO statements are fine. I like them and find it leads to cleaner, easier to understand code. The speghetti code thing is a myth with plenty of examples to disprove it in the Linux kernel.

The deeply nested allocations example *should* be solved by factoring out local/static helper functions...In other words: if your code is too complicated to use GOTO's properly for cleanup, then your code is too complicated.

Re: deeply nested allocations example should be solved by factoring out

Posted Dec 27, 2014 20:42 UTC (Sat) by ldo (guest, #40946) [Link] (6 responses)

Fine. I have offered my example; feel free to rewrite it to prove your point, and then we can compare.

Re: deeply nested allocations example should be solved by factoring out

Posted Dec 27, 2014 20:56 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

I rewrote a sample. It's shorter and easier to read and understand. I provided you a sample of non-trivial cleanup logic from a big project.

What else do you want?

Re: What else do you want?

Posted Dec 27, 2014 21:33 UTC (Sat) by ldo (guest, #40946) [Link]

An example that proves that you can deal gracefully with all the cases that my code manages.

Re: deeply nested allocations example should be solved by factoring out

Posted Jan 1, 2015 0:27 UTC (Thu) by reubenhwk (guest, #75803) [Link] (3 responses)

Please keep an eye out for pull requests...

https://github.com/ldo/dvd_menu_animator/pull/2

Re: deeply nested allocations example should be solved by factoring out

Posted Jan 1, 2015 4:23 UTC (Thu) by flussence (guest, #85566) [Link] (1 responses)

Methinks the crank is polishing his résumé to go apply for GNOME commit access.

Re: deeply nested allocations example should be solved by factoring out

Posted Jan 1, 2015 4:40 UTC (Thu) by reubenhwk (guest, #75803) [Link]

Is there an open position?

Re: deeply nested allocations example should be solved by factoring out

Posted May 23, 2017 13:10 UTC (Tue) by mirabilos (subscriber, #84359) [Link]

Interestingly enough, this got *deleted* (probably by ldo?).

goto bike shed

Posted Dec 27, 2014 17:44 UTC (Sat) by itvirta (guest, #49997) [Link] (8 responses)

> No! No GOTOs. They don’t nest easily, and they lead to spaghetti code. Look at the
> example code I linked above, and think how it would look with GOTOs all over the place.
> Avoid GOTOs!

> for(...) {
> if (PyErr_Occurred()) break;
> }
> if (PyErr_Occurred()) break;

I'm not sure I'd agree that breaking out of a loop just to test the same error condition,
to then only break out of another loop is any clearer than just jumping out directly.

Like someone mentioned, some other programming languages have dedicated constructs
(like exceptions) that can break out of multiple loops. It's not very different from what goto
was recommended for in this case.

(The thing with absolute rules is, that they absolutely forbid one from thinking. That usually
doesn't lead to anything good, so I would advise against it.)

> Fine. Try reworking the example I gave above, then. That has allocations nested up to three levels
> deep, as well as loops. See how well that works using GOTOs.

Reducing the nesting level and using a less space-hungry indenting style would be what I'd start with,
if I were to do this exercise for you.

Re: not sure I'd agree that breaking out of a loop just to test the same error condition

Posted Dec 27, 2014 20:46 UTC (Sat) by ldo (guest, #40946) [Link] (7 responses)

If you look at my code, you will see that each nested level has to do its own cleanup before propagating the error condition onwards. That is the whole point of the nesting.

Re: not sure I'd agree that breaking out of a loop just to test the same error condition

Posted Dec 27, 2014 20:57 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

Really? What cleanup is performed here: https://github.com/ldo/dvd_menu_animator/blob/master/spuh... ?

Or here: https://github.com/ldo/dvd_menu_animator/blob/master/spuh... ?

I actually don't see complicated cleanups anywhere in your code.

Re: What cleanup is performed here:

Posted Dec 27, 2014 21:36 UTC (Sat) by ldo (guest, #40946) [Link]

Try here or here.

Re: not sure I'd agree that breaking out of a loop just to test the same error condition

Posted Dec 28, 2014 3:27 UTC (Sun) by reubenhwk (guest, #75803) [Link] (4 responses)

>> If you look at my code, you will see that each nested level has to do its own cleanup before
>> propagating the error condition onwards. That is the whole point of the nesting.

Better yet, use a function for each of those nested levels. Worried about spaghetti code? Then factor out the nesting and call smaller functions with less looping and less nested resource management. Use the return value to propagate error conditions onward.

Re: Better yet, use a function for each of those nested levels.

Posted Dec 28, 2014 6:34 UTC (Sun) by ldo (guest, #40946) [Link] (3 responses)

Fine. Rewrite some suitably representative part of my code to show us an example of what you mean. There seems to be an enormous reluctance among you so-called programmers to actually do this. Perhaps because every time you try it, you get it wrong.

Re: Better yet, use a function for each of those nested levels.

Posted Dec 29, 2014 2:58 UTC (Mon) by reubenhwk (guest, #75803) [Link]

Perhaps we're on vacation and, even if we weren't, we have better things to do..

Re: Better yet, use a function for each of those nested levels.

Posted Dec 29, 2014 3:19 UTC (Mon) by bronson (guest, #4806) [Link] (1 responses)

Interesting use of the word "us". The royal we?

Re: Better yet, use a function for each of those nested levels.

Posted Dec 29, 2014 17:30 UTC (Mon) by nix (subscriber, #2304) [Link]

Probably the millions of lurkers who support him in email, using his fabulously readable coding style. I know I've encountered it everywhere! (... wait, that should be "nowhere".)

The argument from popularity is not a good one, but if something is not popular it is not terribly wise to imply that in fact it is.

Re: There would be precisely as many "goto" statements

Posted May 23, 2017 13:09 UTC (Tue) by mirabilos (subscriber, #84359) [Link]

It’d even be _easier_ in the case of nested loops, as something like shell’s “break 2” does not exist in C. A sole goto, to the shared exit path.

Avoiding GOTO at all cost is overreacting. The “rule” is probably good to teach to novice programmers, but experts are beyond it. Error handling is *the* prime example in favour of GOTO, although I agree there may be others.

Re: Wouldn't it be simpler and more readable to use a goto instead of a pseudo-loop?

Posted Dec 25, 2014 22:36 UTC (Thu) by vonbrand (subscriber, #4458) [Link] (7 responses)

Please, no knee-jerk "no goto ever" reactions, go read Knuth's "Structured programming with goto statements", ACM Computing Surveys 6(4), dec 1974, pp 261-301. Check how goto is used in the kernel, write up gotoless code doing the same. You'll find that the gotoless code is easier to understand and often significantly more efficient.

Re: Please, no knee-jerk "no goto ever" reactions

Posted Dec 25, 2014 23:08 UTC (Thu) by ldo (guest, #40946) [Link] (6 responses)

Fine. Go and rewrite my code to use GOTOs, and see how you do.

Re: Please, no knee-jerk "no goto ever" reactions

Posted Dec 30, 2014 2:10 UTC (Tue) by filipjoelsson (guest, #2622) [Link] (2 responses)

I thought it would be a fun exercise to rewrite your code with the exact same structure that you used. But instead of the do { /* code */ } while (false); construct - I'd use goto cleanup. The point of this would have been to prove to you that what you are doing is in fact to use goto, but in a circumspect manner.

You do realize that your construct will optimize to exactly the same code, when compiled, right? So, that all you do is add empty words and pointless levels of indent, that may or may not help compilers and other programmers understand what you mean?

So I took a dive into your code, stripped out all the comments and newlines, ran it through indent, and tried again.

And I must say that I believe that do { /* code */ } while (false); is one of your smaller sins!

Why the f*ck do you for instance do things like this?

for (i=0;;) { 

if (i == nrcolors) break; 

/* code */ 

++i;

}

Breaking expectations like that do not anything of value, and makes sure nobody else will want to bother helping out on your project.

You also have nuggets like:

if (nrhistentries <= 4 || /* other condition */)

      {

        if (nrhistentries > 0) {

          histogram[0].index = 0;

          if (nrhistentries > 1) {

            histogram[1].index = 1;

            if (nrhistentries > 2) {

              histogram[2].index = 2;

              if (nrhistentries > 3) {

                histogram[3].index = 3;

              }

            }

          }

        }

Which I would like to replace with:


int max_histentries = (nrhistentries>4)?4:nrhistentries;

for (i=0; i<max_histentries; ++i) {

    histogram[i].index = i;

}

I also wonder what the point is of putting semicolons after comments.

In conclusion: I was in your camp until this discussion started - I really never ever use goto. You, however, have convinced me that there are reasonable exceptions to that rule.

Re: Why the f*ck do you for instance do things like this?

Posted Dec 30, 2014 20:42 UTC (Tue) by ldo (guest, #40946) [Link] (1 responses)

I have this convention: if one of the exits from a loop is via an explicit break, then all exits from the loop shall be via explicit breaks. That way you don’t have to look for more than one kind of termination condition, just look for the breaks. Only if there are none will there be something like a for-loop termination condition. Never mix the two.

Re: Why the f*ck do you for instance do things like this?

Posted Dec 30, 2014 21:12 UTC (Tue) by filipjoelsson (guest, #2622) [Link]

Then don't use a for-loop for that. Use a do-while-loop. A for-loop is for iterating until a certain condition is met. The compiler is built to warn on relevant error patterns. Since you use the for-loop in this unexpected way - no one but you can contribute to your project. In effect it's only so much dead code.

Is there any construct that you use as intended?

Re: Please, no knee-jerk "no goto ever" reactions

Posted Dec 30, 2014 3:00 UTC (Tue) by flussence (guest, #85566) [Link] (2 responses)

Your code already uses gotos - albeit each one rendered with an indented, gaudy costume of do-break-while-0 euphemism.

But the compiler can see your royal highness is stark naked. And so can we.

Re: Please, no knee-jerk "no goto ever" reactions

Posted Dec 30, 2014 9:47 UTC (Tue) by anselm (subscriber, #2796) [Link] (1 responses)

GOTO used to be a real problem when it was all that people had for control flow (think 1960s-era FORTRAN).

Right now with the proper discipline I don't have a huge problem with “goto” in C. As far as I'm concerned it is way less of a problem for program structure than the style that ldo is advocating. ldo's style also seems to presuppose that “cleanup” consists exclusively of undoing earlier things in reverse order; in general one might have to do things in an error branch that one might not have to do during normal flow, and sorting these cases out just serves to make the code even more convoluted on top of all the extraneous “do { … } while (0)” and “if (…) break” constructs.

I teach programming as my day job (some of the time, anyway), and I can guarantee that anybody who came to me with code like ldo's would get a very stern talking-to.

Re: in general one might have to do things in an error branch that one might not have to do during normal flow

Posted Dec 30, 2014 20:53 UTC (Tue) by ldo (guest, #40946) [Link]

I believe this is another instance of the “cleanup” versus “rollback” argument made elsewhere. See my comments about idempotency of deallocation routines and NULLing subsumed pointers.

Re: Wouldn't it be simpler and more readable to use a goto instead of a pseudo-loop?

Posted Dec 25, 2014 22:41 UTC (Thu) by viro (subscriber, #7872) [Link] (28 responses)

Don't get religious, please. goto can easily be abused, but your cute trick with do-while(false) is no better - it avoids the Bad Word(tm), but it's limited to idempotent cleanups (i.e. you'll end up breeding a bunch of flags for "do I need to drop this lock", etc., and it makes for hard-to-verify logics just as easy as goto abuse) *and* it's asking for trouble when you modify the code around that break. E.g. a loop or switch added, with location in question ending up inside the body.

It's both unidiomatic and brittle. Avoiding goto is generally a good idea, but this isn't a good way to do it.

Re: E.g. a loop or switch added,

Posted Dec 25, 2014 23:10 UTC (Thu) by ldo (guest, #40946) [Link] (27 responses)

That code already has plenty of loops in it, and you can see for yourself how to keep the interactions simple in that situation.

This isn’t a question of “religion”, it’s one of “bitter experience”. Learn from it!

Re: E.g. a loop or switch added,

Posted Dec 26, 2014 0:03 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (26 responses)

Actually, no. That's a religion.

Experience shows that idiomatic "goto error_exit" is far better than the alternatives with fake loops and flags.

Re: Experience shows that idiomatic "goto error_exit" is far better than the alternatives with fake loops and flags.

Posted Dec 26, 2014 0:36 UTC (Fri) by ldo (guest, #40946) [Link] (25 responses)

Prove it. You have my code. Go rewrite it.

Re: Experience shows that idiomatic "goto error_exit" is far better than the alternatives with fake loops and flags.

Posted Dec 26, 2014 1:32 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (24 responses)

This particular piece? In ANSI C it'll be something like the code below. In a more sane language I'd use automatic resource management (even in C with GCC extensions).

I won't bother to rewrite all of the code, so only for ParseColorTuple: https://gist.github.com/Cyberax/4546471dcb026c141369 (sorry for possible issues with indentation).

It's now 10 lines less and much more concise (WTF are you incrementing the for-loop variable manually and then manually check conditions?).

I've also fixed a bug in line 246 (failure to check error immediately).

Re: I won't bother to rewrite all of the code, so only for ParseColorTuple:

Posted Dec 26, 2014 2:12 UTC (Fri) by ldo (guest, #40946) [Link] (23 responses)

At least you made the effort, even if you “fixed” a non-bug and succeeded in introducing a real bug.

This was a simple, almost trivial case. Now try a more complex one. Elsewhere you will see do-once constructs nested up to 3 deep. And then there’s loops. Try and see how well your goto constructs scale up to those complexities.

Re: I won't bother to rewrite all of the code, so only for ParseColorTuple:

Posted Dec 26, 2014 4:59 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (22 responses)

> and succeeded in introducing a real bug.
Where?

> This was a simple, almost trivial case. Now try a more complex one.
You can do it _automatically_ by rewriting do-nothing loops into 'goto cleanup' and merging cleanup actions if needed.

> Elsewhere you will see do-once constructs nested up to 3 deep.
That's not something to be proud of, you know. It means that you've failed to decompose your logic into smaller fragments.

And the rest of your code...

It pretty much falls into the 'unmaintainable crap' bin. Everything is just perfect: eclectic code style, exotic constructs (inner functions in... C?), profligate usage of goto disguised as do..nothing loops, functions spanning hundreds of lines, etc.

Re: It pretty much falls into the 'unmaintainable crap' bin

Posted Dec 26, 2014 5:34 UTC (Fri) by ldo (guest, #40946) [Link] (20 responses)

Too bad, that your programming ideas only work with toy examples, not with real-world code.

Come back when you’ve learned a bit more about programming.

Re: It pretty much falls into the 'unmaintainable crap' bin

Posted Dec 26, 2014 5:40 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (13 responses)

> Too bad, that your programming ideas only work with toy examples, not with _real-world code_.
Like... I don't know, say an OS kernel?

Or perhaps an audio codec? Nah, can't write those with gotos: https://git.xiph.org/?p=opus.git;a=blob;f=src/opus_encoder.c;...

Re: Or perhaps an audio codec?

Posted Dec 26, 2014 21:21 UTC (Fri) by ldo (guest, #40946) [Link] (12 responses)

While I’m sure it is quite complex code, it doesn’t seem to do much with dynamic storage: I found just two calls to opus_free in those 2500-odd lines.

While my example is half that size, it has 39 calls to PY_{,X}DECREF.

Come back when you can cope with that kind of complexity.

Re: Or perhaps an audio codec?

Posted Dec 26, 2014 21:25 UTC (Fri) by Cyberax (✭ supporter ✭, #52523) [Link] (11 responses)

Your wish is my command: http://lxr.free-electrons.com/source/drivers/net/tun.c#L1741

Re: Your wish is my command

Posted Dec 27, 2014 20:56 UTC (Sat) by ldo (guest, #40946) [Link] (10 responses)

Now try one with a loop.

Re: Your wish is my command

Posted Dec 27, 2014 20:58 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link] (9 responses)

What do you mean by "with a loop"? And feel free to try it yourself, since you're such a religious fanatic of do-nothing loops.

Re: What do you mean by "with a loop"?

Posted Dec 27, 2014 21:43 UTC (Sat) by ldo (guest, #40946) [Link] (8 responses)

My code has examples of loops where errors can occur in them. So I need to deal gracefully with that. Let’s see you offer an example that does the same.

And while we’re at it, your tun.c example fails to recover if it cannot create its sysfs device files.

Re: What do you mean by "with a loop"?

Posted Dec 27, 2014 22:01 UTC (Sat) by Cyberax (✭ supporter ✭, #52523) [Link] (7 responses)

> My code has examples of loops where errors can occur in them. So I need to deal gracefully with that.
No you don't. Just split them up into free-standing functions, instead of 300-line monstrosities.

The Linux kernel manages to do that just fine, somehow.

In particular, your block near line 480 will look like this:
https://gist.github.com/Cyberax/3a7796231be66d0f64cc
(no, I'm not going to check it in details). It's pretty clear that simply by splitting some logic into a function you can decrease nesting level by 3.

And let me reiterate, your code is a mess. For example, you use 'break' to normally exit the outer loop from within the 'if' statement here: https://github.com/ldo/dvd_menu_animator/blob/master/spuh...

Why do you even bother with 'for' loops?

Re: And let me reiterate, your code is a mess.

Posted Dec 28, 2014 6:29 UTC (Sun) by ldo (guest, #40946) [Link] (6 responses)

At least it works, unlike your code.

Your for-loop will never iterate.
Where is PixBuf supposed to be local to?

Pot calling the kettle black, as it were?

Re: And let me reiterate, your code is a mess.

Posted Dec 28, 2014 6:31 UTC (Sun) by Cyberax (✭ supporter ✭, #52523) [Link] (5 responses)

I have not claimed that my code works (as I wrote it on a dumb web form without even automatic indentation). But it's far easier to understand and fix than your mess of twisty little loops, all alike.

Re: I have not claimed that my code works

Posted Dec 28, 2014 6:36 UTC (Sun) by ldo (guest, #40946) [Link] (4 responses)

Then what is the point? I thought you were trying to demonstrate that you could do the same thing more simply and/or clearly than I could. But instead you have totally stuffed it up.

Re: I have not claimed that my code works

Posted Dec 28, 2014 6:41 UTC (Sun) by Cyberax (✭ supporter ✭, #52523) [Link] (3 responses)

I don't really care to try to understand what your code actually means. It's so convoluted that it's absolute unmaintainable.

If you can make a reasonable description of what it does - I can guarantee that it's possible to write it far cleaner then what you have.

Re: If you can make a reasonable description of what it does

Posted Dec 28, 2014 21:33 UTC (Sun) by ldo (guest, #40946) [Link] (2 responses)

Did you not read the comments? There are even Python docstrings; did you not see those?

Re: If you can make a reasonable description of what it does

Posted Dec 28, 2014 22:37 UTC (Sun) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

No, they don't describe the algorithm. Please, provide a coherent description in a natural language (I understand English, Russian, Ukrainian, German and Polish) then I can provide you its implementation that will be more compact and easy-to-understand than yours.

Re: Please, provide a coherent description

Posted Dec 29, 2014 17:26 UTC (Mon) by ldo (guest, #40946) [Link]

Funny, I didn’t see any such thing in the code examples you saw fit to refer me to. Yet you expected me to cope with them. And my code already has far more comments than they did.

What’s good for the goose, eh?

Re: It pretty much falls into the 'unmaintainable crap' bin

Posted Dec 26, 2014 16:14 UTC (Fri) by mb (subscriber, #50428) [Link] (5 responses)

>Too bad, that your programming ideas only work with toy examples, not with real-world code.

This is like the guy complaining about _all_ those damn ghost drivers on the highway.

Huge projects use goto for error handling successfully. See the Linux kernel for instance.
And your "nested pseudo loops error handler" argument is void, because thouse unmaintainable monsters should be split into sub-routines anyway. And then it can use plain gotos. Which gains the additional opportunity to write structured error paths instead of "one must handle all errors" error paths.

Re: Huge projects use goto for error handling successfully

Posted Dec 26, 2014 21:15 UTC (Fri) by ldo (guest, #40946) [Link] (4 responses)

Or perhaps not so successfully. Otherwise we would not have this article.

Re: Huge projects use goto for error handling successfully

Posted Dec 27, 2014 11:32 UTC (Sat) by mb (subscriber, #50428) [Link] (3 responses)

The article talks (as a side note) about untested error paths.
Your complex pseudo-loop can't help here at all. It just adds extra complexity. The error paths will still be untested.

Re: The error paths will still be untested.

Posted Dec 27, 2014 20:40 UTC (Sat) by ldo (guest, #40946) [Link] (2 responses)

It makes them easier to see. That helps in writing the code in the first place.

Re: The error paths will still be untested.

Posted Dec 27, 2014 23:14 UTC (Sat) by vonbrand (subscriber, #4458) [Link] (1 responses)

The pseudo-loops hide the error processing in a structure that could be anything else, and which BTW I haven't seen anywhere else either. ln comparison, the "label: <error handling code>" pattern is easy to spot.

Re: The pseudo-loops hide the error processing

Posted Dec 28, 2014 6:33 UTC (Sun) by ldo (guest, #40946) [Link]

No, the cleanups always happen after the do-once constructs. That’s how you can be sure they will always be executed.

Re: I won't bother to rewrite all of the code, so only for ParseColorTuple:

Posted Dec 26, 2014 16:30 UTC (Fri) by nix (subscriber, #2304) [Link]

(do/once constructs nested up to three deep)

That's not something to be proud of, you know. It means that you've failed to decompose your logic into smaller fragments.

Actually it means he's probably trying to do multiple things which need unwinding, but because he can't use three goto labels and rely on fallthrough he has to add a layer of almost-entirely-redundant nesting for each one.

This is not something that you'd call out as an advantage and a sign of great experience unless you didn't actually have much. (But it's been worth reading this thread anyway: it's not every day you see people telling Al Viro that he doesn't have enough experience to judge the relative worth of exception-handling goto versus other techniques!)

Or You Could Simplify The Error-Recovery Paths