This Week on p5p 2000/11/14

Nov 14, 2000 by Simon Cozens

Notes
stat vs. lstat
Threads and POSIX
PerlIO
README.Solaris
Locales
Integer handling revisited
=head3
Little fixes
Various

Notes

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There were 348 messages this week.

Dominus mentioned this during his tenure, but now it’s my turn: these reports are only made possible due to the generosity of O’Reilly and Associates, who keep me in caffeine.

stat vs. lstat

David Dyck was using find2perl and turned up a couple of problems with lstat. The problem is that lstat _ produces a warning because it thinks that _ is a filehandle, and you can’t lstat a filehandle. (Only a filename)

David produced a patch to take care of this, but then discovered that lstat and the -l filetest were acting differently; you shouldn’t be allowed to follow stat('something') with lstat _. Again, David produced another patch to cause a fatal error if you try.

He also noticed that -l FH dies, whereas lstat FH doesn’t, but nobody has looked into that yet.

Also in the “file tests” area, Rich Morin quoted the camel book:

“Because Perl has to read a file to do the -T test, you don’t want to use -T on special files that might hang or give you other kinds of grief.”

and commented that maybe Perl should test to see whether someone is planning to do a -T or a -B test on a special file, and “keep itself out of trouble”.

Kurt Starsinic pointed out that there were times when you do want to test, for example, a named pipe, and Perl shouldn’t restrict the programmer from doing so. Nick said it’ll all be OK when we have PerlIO working.

Threads and POSIX

Kurt was indulging in bug archaeology and turned up something spooky relating to signals and threads. He asked for an explanation of how the signal model changes between nonthreaded and threaded Perl, which Dan Sugalski duly provided. The rest of that thread (ho, ho) is worth reading, if you’re interested in how threads work with Perl.

PerlIO

As usual, there’s a lot of good work going on with PerlIO, and quite a lot of the bulk of this week’s traffic was taken up with PerlIO-related test results, bug reports and discussion.

To remind you, PerlIO is going to be a complete IO library for Perl, which, among other things, allows us to insert filters at various stages of the input and output process. This means that, for instance, data can be transparently converted to UTF8 from other character sets.

Nick mentioned that he’d like to test PerlIO a lot, so it would be appreciated if those following the Perl development sources could do something like the following:

    ./Configure -Duseperlio -d
    make
    ...
    PERLIO=stdio  make test
    PERLIO=perlio make test
    PERLIO=mmap   make test

and report results. ( mmap may not be available, depending on platform.) Dominic Dunlop fixed the MachTen hints to stop it for claiming to support mmap, since any attempt to use the function just causes the program to abort due to an error.

Robin Barker found that PerlIO-over- stdio breaks large file support; Nick found that this was a problem with 64-bit support and that Perl was using fseek where it should have been using fseeko.

Nicholas Clark did some work on IO::Handle and some other IO calls, and found that the return values weren’t particularly intuitive; Perl was reporting the raw return values from stdio rather than true or false. This becomes problematic, of course, when the IO model isn’t stdio. He produced some fixes for ungetc and getpos, and he also noted that if we’re using sfio then we shouldn’t treat sftell as if it were ftell, as there’s yet another return value inconsistency.

Nicholas also came up with a “dumb shell”to allow a shell with a per-process current directory on systems that don’t have one, which should make dealing with subdirectories during building easier, and might also help with cross-compiling Perl.

Nick Ing-Simmons also asked

Now that PerlIO is in the mainline I _really_ need to know what to do next in terms of making it useful.

This means knowing what it “should” look like to perl5

There followed a useful discussion of the proposed API; Read about it.

It was also determined that one should open a file containing Latin data as follows:

[ XL indementum tum biguttam tum latin-1 inquementum tum LatinFile inquementum evolute meo fho morive errorum. ]

and that Perl programs dealing with data in Japanese are implicity permitted to seppuku.

README.Solaris

Andy Dougherty produced a README.Solaris, which Jarkko, Russ, Alan and many others looked over and improved; later on, he produced a final version to be integrated, along with some other Solaris fixes. This was applied to the tree, and then some people picked over it a little more. Read about it.

Locales

Jarkko’s old nemesis was out in force this week. Robin Barker and Larry Virden found that the UTF8 locales didn’t work properly - this was not really a surprise, since Jarkko had disabled the tests as they require the fabled polymorphic regular expression support. (This means that /(.)/ should be equally happy capturing a UTF8 character as a non-UTF8 character.) Lupe Christoph found that most of the tests work OK, as there’s only two that require polymorphic regexes. Jarkko grudgingly re-enabled them - locales are Not His Friend.

Vadim Konovalov produced a little fix to make the locale tests work, and added a test for the MS-DOS Russian code page; seems like Perl is now happy to speak Russian even on MS-DOS systems.

Integer handling revisited

If you remember a month ago, there was a discussion on integer and floating point handling, in which it was suggested that adding two integers together at run-time should result in an integer, rather than a floating point.

Jarkko and Nicholas Clark have been looking into this, and Jarkko produced a patch; it looked to me like the complexity of determining whether it’s possible to sum two integers without overflowing is going to cause a slowdown, and Perl usually trades space for speed.

However, Nicholas mentioned that on the StrongARM architecture, floating points are all emulated, and thus keeping everything integer might actually speed it up.

=head3

Casey Tweten produced a patch that allowed Pod::Man to deal with =head3 and above. Russ Allbery disapproved, on the grounds that the man translator should not be singled out - if we’re going to do this, we should change the documentation for POD, and all the other translators. Andy pointed out that it’s OK to update the translators one at a time, since it’s not really reasonable to blitz through them all in one go. However, perlpod.pod should be updated. (Nobody’s done this yet.)

Tim Jenness pointed out that the LaTeX translator already deals with =head3 and =head4.

Little fixes

Since last week, I concentrated on things that nobody fixed, this time we’ll have a whirlwind tour of things that people did get fixed.

The VMS and Cygwin flock fix we mentioned last week were implemented, thanks to Craig Berry and Andy Dougherty.

Eric Fifer brought the Cygwin port up to date with Cygwin 1.1.5. (Great work as ever, Eric!)

Harold Morris, one of the Amdahl UTS people produced some patches to help Perl run under UTS; Lupe Christoph had some of the regular expression-test suite explain why it was failing if it did. Lots of people fixed up documentation, so I won’t mention them all. Casey Tweten did some good work, including adding an import method to Class::Struct. Nicholas Clark fixed some FreeBSD stdio declarations. Robin Barker picked up some dodgy casts between pointers and integers.