[Bug libc/15009] New: tdestroy() should allow passing 'NULL' for 'free_node' callback

[Bug libc/15009] New: tdestroy() should allow passing 'NULL' for 'free_node' callback

[ivosh at ivosh dot net]

http://sourceware.org/bugzilla/show_bug.cgi?id=15009

             Bug #: 15009
           Summary: tdestroy() should allow passing 'NULL' for 'free_node'
                    callback
           Product: glibc
           Version: 2.17
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: ivosh@ivosh.net
                CC: drepper.fsp@gmail.com
    Classification: Unclassified


Created attachment 6811
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6811
source code patch proposal

This is a modest enhancement which would make lives of many developers
a bit more cheerful.

Glibc contains function tdestroy() which is not specified by any standard.
This function is very handy because it allows destroying whole binary
search tree at once.

However the 'free_node' callback cannot be NULL even if no work
is necessary (keys are integers, for example).
I can only speculate why it is so. The only valid reason might be performance:
  (*freefct) ((void *) root->key);
could be called directly in tdestroy_recurse() without checking for
non-NULL first.

However that puts unnecessary burden on the application developers,
although the manpage says that 'free_node' in that case must point to
an empty function. Even glibc itself has such empty function (freenop).

Glibc should be more friendly in this case and allow to pass NULL
for 'free_node".

See the attached patch with my proposal.
If the patch will be accepted, documentation and tdestroy()
invocation(s) with empty functions need to be revisited.
I can supply these as well.

------------------------------
Required information:

Glibc version: 2.17
Host/build/target: any

> uname -a
Linux xxxxx 3.2.0-35-generic #55-Ubuntu SMP Wed Dec 5 17:42:16 UTC 2012 x86_64
x86_64 x86_64 GNU/Linux

> gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.6.3-1ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object
--enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686
--with-tune=generic --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5) 

> ld -v
GNU ld (GNU Binutils for Ubuntu) 2.22

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[Bug libc/15009] tdestroy() should allow passing 'NULL' for 'free_node' callback

[schwab@linux-m68k.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=15009

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

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[Bug libc/15009] tdestroy() should allow passing 'NULL' for 'free_node' callback

[ondra at iuuk dot mff.cuni.cz]

http://sourceware.org/bugzilla/show_bug.cgi?id=15009

OndrejBilka <ondra at iuuk dot mff.cuni.cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ondra at iuuk dot
                   |                            |mff.cuni.cz

--- Comment #1 from OndrejBilka <ondra at iuuk dot mff.cuni.cz> 2013-05-21 14:30:09 UTC ---
Could you post this patch to libc-alpha@sourceware.org?

Please read http://sourceware.org/glibc/wiki/Contribution%20checklist for
requirements.

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[Bug libc/15009] tdestroy() should allow passing 'NULL' for 'free_node' callback

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15009

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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