This Week on p5p 1999/12/12

Dec 12, 1999 by Mark-Jason Dominus

Notes

This report covers the week of the release of 5.005_63, so traffic suddenly surged. Catching up by Sunday now looks unlikely, but I am getting closer.

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5.005_63 Released

Sarathy’s Announcement includes a list of changes and a substantial TODO list for 5.005_64.

There was the usual collection of bug reports that follows a new release, mostly concerning compilation and configuration issues.

Dan Sugalski: Too late to slip in support for open(RW, "| foo |")? Sarathy: Yes, unless you can convince me that it’s life-threatening. :-)

Tom also posted a to-do list about messages that are in the source but not documented in perldiag.

Sarathy and Dan Sugalski’s discussion of the new threading model continued. Read about it.

Development Continues on Ilya’s Patches

Regex Optimizations

Sarathy’s failure case for Regex Optimization Patch does not fail when Ilya tries it. Ilya suspects version slippage. It looks like this did make it into 5.005_63.

PREPARE

Sarathy and Ilya discussed the PREPARE patch. Unfortunately, I cannot evaluate the discussion yet. Ilya did submit an additional patch to fix a bug about which Sarathy had said ``I don’t know how this could have ever worked at your end.”

PREPARE did not get into 5.005_63.

XSLoader

Sarathy supplied a patch to eliminate the many warnings caused by replacement of DynaLoader.pm with XSLoader.pm. The XSLoader stuff went into 5.005_63.

Change to xsubpp

In spite of the favorable test reports from last week, Ilya’s xsubpp patch did not get into 5.005_63. I was not quite clear on why not. Sarathy said that the patch was incomplete and not robust, but only specified that there was a lack of documentation and that there was no way to disable the change. Ilya protested that there are zillions of xsubpp features that cannot be disabled.

Patch Location

Ilya made up packages of his patches that were not accepted for 5.005_63. Read about it.

New Improved File::Find

Helmut Jarausch contributed a new and improved version of File::Find. Here is Helmut’s original message, which summarizes the new features. (Or see perldelta in 5.005_63.)

DB_File Locking Technique

Paul Marquess reported that the file locking strategy suggested by the DB_File documentation didn’t work. It suggested something like this:

    $db = tie(%db, 'DB_File', ...) or die ...;
    $fd = $db->fd;
    open(DB_FH, "+<&=$fd") or die ...;
    flock (DB_FH, LOCK_EX) or die ...;
    ...
    flock(DB_FH, LOCK_UN);
    undef $db;

Problem: The tie itself opens the file, which causes the stdio library to read and cache some data from the database. But this occurs before the file is locked. Therefore there is a race condition here. This method also appears in the Camel and Ram books. Paul posted a message describing the problem in detail, including solutions. One of these solutions is to simply lock some other file instead of the database file itself; this is also a general solution to many similar problems.

David Harris was the person who originally reported this problem to Paul. He has a detailed description of it online.

Some other miscellaneous discussion of locking followed. Raphael Manfredi posted a new version of his LockFile::Simple module that provides simple lock and unlock functions to do advisory locking. This did not appear in 5.005_63.

use Parameters in XS Module Initializations

Ilya posed this problem: He has a module, Math::Pari, which is dynamically loaded. He wants to be able to say

    use Math::Pari qw(:primelimit=1e8 :stack=20e6 :prec=128);

and have the qw(...) items affect the initialization of the Math::Pari module, which is done when it is bootstrapped. But the items are passed to the import() function, which is called after the module is loaded, bootstrapped, and initialized, and therefore too late. One possibility, advocated by Joshua Pritikin, is to ask the user to write this instead:

    use Math::Pari::Init qw(:primelimit=1e8 :stack=20e6 :prec=128);
    use Math::Pari;

Ilya does not like that.

Larry suggested that

    use Math::Pari qw(:primelimit=1e8 :stack=20e6 :prec=128);

could be made to mean

    BEGIN {
        local @Math::Pari::ARGV = qw(:primelimit=1e8 :stack=20e6 :prec=128);
        require Math::Pari;
        Math::Pari->import(@Math::Pari::ARGV);
    }

next in XS-invoked Perl subroutines

Gisle Aas and Michael A. Chase report that if you try to use next in a Perl subroutine that was invoked from an XS procedure, Perl dumps core. No news on this this week.

-Dp improvement

The -Dp option prints debugging information for parsing and tokenizing. It is extremely verbose, so you would like to use

    BEGIN { $^D |= 1 }
    somecode
    END  { $^D &=  ~1 }

to enable -Dp just for the code of interest. Formerly, this worked for tokenizing but not for parsing; Stéphane Payrard submitted a patch to make it work for parsing also.

Log::Agent

Raphael Manfredi announced his Log::Agent module, which allows modules to issue log messages in the way that the main application directs. The same module might log to a file, to nowhere, or to syslog, depending on the wishes of the application into which it is embedded.

I think this is a good idea. It can be very difficult to get modules to shut up. I identified this as one of the Sins of Perl in my article last month.

It did not appear in 5.005_63.

Getopt::Long Documentation

Johan Vromans rewrote the Getopt::Long documentation.

lex_fakebrack Horrors

Last week, Mike Guy complained that the lexing of forms involving ${a[0]} and ${h{k}} was inconsistent. (These are in there so that you can force Perl to interpret the [0-9] in /...$a[0-9]/ as an array subscript rather then a character class.) Larry supplied a patch.

Larry: I’m working on this one, in case anyone else was thinking about it. Basically, lex_fakebrack needs to go away. Ilya: Thanks. There are not so many totally incomprehensible places in toke.c, andlex_fakebrack is one of them.

I wanted to include the relevant code so that everyone would have a chance to see what it was that Ilya considers totally incomprehensible. But of course this is impossible, because if it were a small, compact piece of code then it would not have been totally incomprehensible. Instead it riddled toke.c like a small but virulent fungus.

dmake is a version of make for win32 systems. The README.win32 file in the perl distribution refers people to a copy of the sources in one of Sarathy’s personal directories at University of Michigan; Elaine Ashton asked why there was no link to the official site. Sarathy explained that the copy on the official site was severely broken but that his copy worked properly. Elaine also asked why Sarathy’s version wasn’t in his CPAN directory; Sarathy said he had not been sure about whether to put it there or not since it was not directly related to Perl.

Mike Guy pointed out that it would not set a new precedent to put such things on CPAN and suggested that it would be a good idea to put it there.

defined Bug?

Helmut Jarausch points out that

    print "is defined\n"  if defined($H{'x'}++);

does in fact print the message. There was no discussion and I did not see a patch. The behavior persists in 5.005_63.

strict vars Fails to Detect $a and $b

I wouldn’t mention this, except that Robin Berjon suggested compiling a list of the ten most frequently reported non-bugs. I am interested in doing this. It would be useful to me if people would suggest things that I should watch out for. The aforementioned strict vars non-failure is one, and the various localtime Y2Knonbugs are some others. If you have suggestions, please send them to me.

Various

A large collection of bug reports, bug fixes, non-bug reports, questions, and answers. No spam this week, but several people sent messages to the list asking how to unsubscribe, and this prompted an apparently fruitless discussion of how this might be avoided in the future.

Until next time (probably Sunday) I remain, your humble and obedient servant,

Mark-Jason Dominus

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