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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.


       -M <maxsize>
              This sets the maximum cache size. You can specify a  value  in  gigabytes,  megabytes  or  kilobytes  by
              appending a G, M or K to the value. The default is gigabytes. The actual value stored is rounded down to
              the nearest multiple of 16 kilobytes.


INSTALLATION
       There are two ways to use ccache. You can either prefix your compile commands with  "ccache-swig"  or  you  can
       create a symbolic link between ccache-swig and the names of your compilers. The first method is most convenient
       if you just want to try out ccache or wish to use it for some specific projects. The second method is most use-
       ful for when you wish to use ccache for all your compiles.

       To install for usage by the first method just copy ccache-swig to somewhere in your path.

       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 compil-
              ers. 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
              ccache works it out from the command line.


       CCACHE_PREFIX
              This option adds a prefix to the command line that ccache runs when invoking the compiler. Also see  the
              section below on using ccache with distcc.


       CCACHE_DISABLE
              If you set the environment variable CCACHE_DISABLE then ccache will just call the real compiler, bypass-
              ing the cache completely.


       CCACHE_READONLY
              the CCACHE_READONLY environment variable tells ccache to attempt to use existing  cached  object  files,
              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 optimi-
              sation, 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 set-
              ting this environment variable loses a little bit of speed, but it means that ccache can take  advantage
              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 incorrect line
              number information in compiler warning messages.


       CCACHE_EXTENSION
              Normally ccache tries to automatically determine the extension to use for intermediate  C  pre-processor
              files  based  on the type of file being compiled. Unfortunately this sometimes doesn't work, for example
              when using the aCC compiler on HP-UX. On systems like this you can use the  CCACHE_EXTENSION  option  to
              override the default. On HP-UX set this environment variable to "i" if you use the aCC compiler.


       CCACHE_STRIPC
              If you set the environment variable CCACHE_STRIPC then ccache will strip the -c option when invoking the
              preprocessor. This option is primarily for the Sun Workshop C++  compiler  as  without  this  option  an
              unwarranted warning is displayed: CC: Warning: "-E" redefines product from "object" to "source (stdout)"
              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 dif-
       ferent 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 com-
       piled 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 without
       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 com-
       mand '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
       results  in  false dependencies to be triggered by timestamp-based build systems whenever another user links to
       an existing file. Typically, users will see that their libraries and binaries are relinked without reason.   To
       share a cache without side effects, the following conditions need to be met:


       o      Use the same CCACHE_DIR environment variable setting

       o      Unset the CCACHE_HARDLINK environment variable

       o      Make sure everyone sets the CCACHE_UMASK environment variable to 002, this ensures that cached files are
              accessible to everyone in the group.

       o      Make sure that all users have write permission in the entire cache directory (and  that  you  trust  all
              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 com-
              pression.



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

       ccache  is  released  under  the GNU General Public License version 2 or later. Please see the file COPYING for
       license details.





                                                                ccache-swig(1)