HP-UX 11i September 2001 Release Notes

Programming
Libraries
Chapter 13
204
Two defects were fixed in nftw():
• When the FTW_CHDIR option is set, directories are considered unreadable unless they
have both read and execute permissions. (The old nftw() would try to chdir() into
a directory without execute permissions and then abort the walk with an error).
• When the FTW_CHDIR option is set, a directory object is reported to the user function
before it is chdir()'ed into.
nftw() improvements vary depending on options provided, with the most significant
improvements seen in UNIX95 standard mode with the FTW_PHYS option not set, or
when a very large number of directories exist in the file tree being traversed.
Documentation Change The ftw (3C) and nftw (3C) manpages have been updated,
particularly with respect to the two defect fixes and means of achieving best concurrency
in threaded applications.
Other Issues The code size of ftw() and nftw() has increased by about 40%, but the
heap requirements are reduced by 50% or more.
If you relied on the FTW_CHDIR defects which were mentioned above, there may need to
be an application change.
Performance Issues Minimally, you should find that ftw() operates about 6% faster
and nftw() 4% faster. On very large file trees where the number of tracked inodes is in
the tens of thousands or more, the performance gain of nftw() could be 30% to 40% or
more.
Performance Improvements to libc’s malloc(3C)
A new environment variable, _M_CACHE_OPTS, is available to help tune malloc()
performance in kernel-threaded applications. This environment variable configures a
thread-private cache for malloc’ed blocks. If cache is configured, malloc’ed blocks are
placed into a thread's private cache when free() is called, and may thereafter be
allocated from cache when malloc() is called. Having such a cache potentially improves
speed performance for some kernel-threaded applications, by reducing mutex contention
among threads and by deferring coalescence of blocks.
The thread-private cache is only available for kernel-threaded applications, i.e. those
linked with the pthread library. The installed shared pthread library version must be
PHCO_19666 or later, or the application must be statically linked with an archive
pthread library that is version PHCO_19666 or later, or else cache is not available.
By default cache is not active and must be activated by setting _M_CACHE_OPTS to a
legal value. If _M_CACHE_OPTS is set to any out of range values, it is ignored and cache
remains disabled.
There are two portions to the thread private cache: one for ordinary blocks and one for
small blocks. Small blocks are blocks that are allocated by the small block allocator
(SBA), which is configured with the environment variable _M_SBA_OPTS or by calls to
mallopt(3C). The small block cache is automatically active whenever both the ordinary
block cache and the SBA are active. The ordinary block cache is active only when it is
configured by setting _M_CACHE_OPTS. There are no mallopt() options to configure the
thread-private cache.
The following shows _M_CACHE_OPTS’s subparameters and their meaning:
_M_CACHE_OPTS= <bucket_size> : <buckets> : <retirement_age>