ccache-swig(1) ccache-swig(1)
NAME
ccache-swig - a fast compiler cache
SYNOPSIS
ccache-swig [OPTION]
ccache-swig <compiler> [COMPILER OPTIONS]
<compiler> [COMPILER OPTIONS]
DESCRIPTION
ccache-swig is a compiler cache. It speeds up re-compilation of C/C++/SWIG code by caching previous compiles
and detecting when the same compile is being done again. ccache-swig is ccache plus support for SWIG. ccache
and ccache-swig are used interchangeably in this document.
OPTIONS SUMMARY
Here is a summary of the options to ccache-swig.
-s show statistics summary
-z zero statistics
-c run a cache cleanup
-C clear the cache completely
-F <n> set maximum files in cache
-M <n> set maximum size of cache (use G, M or K)
-h this help page
-V print version number
OPTIONS
These options only apply when you invoke ccache as "ccache-swig". When invoked as a compiler none of these
options apply. In that case your normal compiler options apply and you should refer to your compilers documen‐
tation.
-h Print a options summary page
-s Print the current statistics summary for the cache. The statistics are stored spread across the subdi‐
rectories of the cache. Using "ccache-swig -s" adds up the statistics across all subdirectories and
prints the totals.
-z Zero the cache statistics.
-V Print the ccache version number
-c Clean the cache and re-calculate the cache file count and size totals. Normally the -c option should
not be necessary as ccache keeps the cache below the specified limits at runtime and keeps statistics
up to date on each compile. This option is mostly useful if you manually modify the cache contents or
believe that the cache size statistics may be inaccurate.
-C Clear the entire cache, removing all cached files.
-F <maxfiles>
This sets the maximum number of files allowed in the cache. The value is stored inside the cache direc‐
tory and applies to all future compiles. Due to the way the value is stored the actual value used is
always rounded down to the nearest multiple of 16.
To install for the second method do something like this:
cp ccache-swig /usr/local/bin/
ln -s /usr/local/bin/ccache-swig /usr/local/bin/gcc
ln -s /usr/local/bin/ccache-swig /usr/local/bin/g++
ln -s /usr/local/bin/ccache-swig /usr/local/bin/cc
ln -s /usr/local/bin/ccache-swig /usr/local/bin/swig
This will work as long as /usr/local/bin comes before the path to gcc (which is usually in /usr/bin). After
installing you may wish to run "which gcc" to make sure that the correct link is being used.
Note! Do not use a hard link, use a symbolic link. A hardlink will cause "interesting" problems.
EXTRA OPTIONS
When run as a compiler front end ccache usually just takes the same command line options as the compiler you
are using. The only exception to this is the option ’--ccache-skip’. That option can be used to tell ccache
that the next option is definitely not a input filename, and should be passed along to the compiler as-is.
The reason this can be important is that ccache does need to parse the command line and determine what is an
input filename and what is a compiler option, as it needs the input filename to determine the name of the
resulting object file (among other things). The heuristic ccache uses in this parse is that any string on the
command line that exists as a file is treated as an input file name (usually a C file). By using --ccache-skip
you can force an option to not be treated as an input file name and instead be passed along to the compiler as
a command line option.
ENVIRONMENT VARIABLES
ccache uses a number of environment variables to control operation. In most cases you won’t need any of these
as the defaults will be fine.
CCACHE_DIR
the CCACHE_DIR environment variable specifies where ccache will keep its cached compiler output. The
default is "$HOME/.ccache".
CCACHE_TEMPDIR
the CCACHE_TEMPDIR environment variable specifies where ccache will put temporary files. The default is
the same as CCACHE_DIR. Note that the CCACHE_TEMPDIR path must be on the same filesystem as the
CCACHE_DIR path, so that renames of files between the two directories can work.
CCACHE_LOGFILE
If you set the CCACHE_LOGFILE environment variable then ccache will write some log information on cache
hits and misses in that file. This is useful for tracking down problems.
CCACHE_VERBOSE
If you set the CCACHE_VERBOSE environment variable then ccache will display on stdout all the compiler
invocations that it makes. This can useful for debugging unexpected problems.
CCACHE_PATH
You can optionally set CCACHE_PATH to a colon separated path where ccache will look for the real com‐
pilers. If you don’t do this then ccache will look for the first executable matching the compiler name
in the normal PATH that isn’t a symbolic link to ccache itself.
CCACHE_CC
You can optionally set CCACHE_CC to force the name of the compiler to use. If you don’t do this then
but not to try to add anything new to the cache. If you are using this because your CCACHE_DIR is
read-only, then you may find that you also need to set CCACHE_TEMPDIR as otherwise ccache will fail to
create the temporary files.
CCACHE_CPP2
If you set the environment variable CCACHE_CPP2 then ccache will not use the optimisation of avoiding
the 2nd call to the pre-processor by compiling the pre-processed output that was used for finding the
hash in the case of a cache miss. This is primarily a debugging option, although it is possible that
some unusual compilers will have problems with the intermediate filename extensions used in this opti‐
misation, in which case this option could allow ccache to be used.
CCACHE_NOCOMPRESS
If you set the environment variable CCACHE_NOCOMPRESS then there is no compression used on files that
go into the cache. However, this setting has no effect on how files are retrieved from the cache, com‐
pressed results will still be usable.
CCACHE_NOSTATS
If you set the environment variable CCACHE_NOSTATS then ccache will not update the statistics files on
each compile.
CCACHE_NLEVELS
The environment variable CCACHE_NLEVELS allows you to choose the number of levels of hash in the cache
directory. The default is 2. The minimum is 1 and the maximum is 8.
CCACHE_HARDLINK
If you set the environment variable CCACHE_HARDLINK then ccache will attempt to use hard links from the
cache directory when creating the compiler output rather than using a file copy. Using hard links is
faster, but can confuse programs like ’make’ that rely on modification times. Hard links are never made
for compressed cache files.
CCACHE_RECACHE
This forces ccache to not use any cached results, even if it finds them. New results are still cached,
but existing cache entries are ignored.
CCACHE_UMASK
This sets the umask for ccache and all child processes (such as the compiler). This is mostly useful
when you wish to share your cache with other users. Note that this also affects the file permissions
set on the object files created from your compilations.
CCACHE_HASHDIR
This tells ccache to hash the current working directory when calculating the hash that is used to dis‐
tinguish two compiles. This prevents a problem with the storage of the current working directory in the
debug info of a object file, which can lead ccache to give a cached object file that has the working
directory in the debug info set incorrectly. This option is off by default as the incorrect setting of
this debug info rarely causes problems. If you strike problems with gdb not using the correct directory
then enable this option.
CCACHE_UNIFY
If you set the environment variable CCACHE_UNIFY then ccache will use the C/C++ unifier when hashing
the pre-processor output if -g is not used in the compile. The unifier is slower than a normal hash, so
setting this environment variable loses a little bit of speed, but it means that ccache can take advan‐
tage of not recompiling when the changes to the source code consist of reformatting only. Note that
using CCACHE_UNIFY changes the hash, so cached compiles with CCACHE_UNIFY set cannot be used when
CCACHE_UNIFY is not set and vice versa. The reason the unifier is off by default is that it can give
out)" when -E and -c is used together.
CCACHE_SWIG
When using SWIG as the compiler and it does not have ’swig’ in the executable name, then the
CCACHE_SWIG environment variable needs to be set in order for ccache to work correctly with SWIG. The
use of CCACHE_CPP2 is also recommended for SWIG due to some preprocessor quirks, however, use of
CCACHE_CPP2 can often be skipped -- check your generated code with and without this option set. Known
problems are using preprocessor directives within %inline blocks and the use of ’#pragma SWIG’.
CACHE SIZE MANAGEMENT
By default ccache has a one gigabyte limit on the cache size and no maximum number of files. You can set a
different limit using the "ccache -M" and "ccache -F" options, which set the size and number of files limits.
When these limits are reached ccache will reduce the cache to 20% below the numbers you specified in order to
avoid doing the cache clean operation too often.
CACHE COMPRESSION
By default on most platforms ccache will compress all files it puts into the cache using the zlib compression.
While this involves a negligible performance slowdown, it significantly increases the number of files that fit
in the cache. You can turn off compression setting the CCACHE_NOCOMPRESS environment variable.
HOW IT WORKS
The basic idea is to detect when you are compiling exactly the same code a 2nd time and use the previously
compiled output. You detect that it is the same code by forming a hash of:
o the pre-processor output from running the compiler with -E
o the command line options
o the real compilers size and modification time
o any stderr output generated by the compiler
These are hashed using md4 (a strong hash) and a cache file is formed based on that hash result. When the same
compilation is done a second time ccache is able to supply the correct compiler output (including all warnings
etc) from the cache.
ccache has been carefully written to always produce exactly the same compiler output that you would get with‐
out the cache. If you ever discover a case where ccache changes the output of your compiler then please let me
know.
USING CCACHE WITH DISTCC
distcc is a very useful program for distributing compilation across a range of compiler servers. It is often
useful to combine distcc with ccache, so that compiles that are done are sped up by distcc, but that ccache
avoids the compile completely where possible.
To use distcc with ccache I recommend using the CCACHE_PREFIX option. You just need to set the environment
variable CCACHE_PREFIX to ’distcc’ and ccache will prefix the command line used with the compiler with the
command ’distcc’.
SHARING A CACHE
A group of developers can increase the cache hit rate by sharing a cache directory. The hard links however
cause unwanted side effects, as all links to a cached file share the file’s modification timestamp. This
users of the shared cache).
o Make sure that the setgid bit is set on all directories in the cache. This tells the filesystem to
inherit group ownership for new directories. The command "chmod g+s `find $CCACHE_DIR -type d`" might
be useful for this.
o Set CCACHE_NOCOMPRESS for all users, if there are users with versions of ccache that do not support
compression.
HISTORY
ccache was inspired by the compilercache shell script script written by Erik Thiele and I would like to thank
him for an excellent piece of work. See http://www.erikyyy.de/compilercache/ for the Erik’s scripts.
ccache-swig is a port of the original ccache with support added for use with SWIG.
I wrote ccache because I wanted to get a bit more speed out of a compiler cache and I wanted to remove some of
the limitations of the shell-script version.
DIFFERENCES FROM COMPILERCACHE
The biggest differences between Erik’s compilercache script and ccache are:
o ccache is written in C, which makes it a bit faster (calling out to external programs is mostly what
slowed down the scripts).
o ccache can automatically find the real compiler
o ccache keeps statistics on hits/misses
o ccache can do automatic cache management
o ccache can cache compiler output that includes warnings. In many cases this gives ccache a much higher
cache hit rate.
o ccache can handle a much wider ranger of compiler options
o ccache avoids a double call to cpp on a cache miss
CREDITS
Thanks to the following people for their contributions to ccache
o Erik Thiele for the original compilercache script
o Luciano Rocha for the idea of compiling the pre-processor output to avoid a 2nd cpp pass
o Paul Russell for many suggestions and the debian packaging
AUTHOR
ccache was written by Andrew Tridgell http://samba.org/~tridge/. ccache was adapted to create ccache-swig for
use with SWIG by William Fulton.
If you wish to report a problem or make a suggestion then please email the SWIG developers on the swig-devel
mailing list, see http://www.swig.org/mail.html
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