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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 documentation.

       -h     Print a options summary page

       -s     Print the current statistics summary for  the  cache.  The  statistics  are  stored
              spread  across  the subdirectories 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 directory 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 useful 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  compilers. 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, bypassing 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 optimisation, 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, compressed 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 distinguish 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 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 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  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 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 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 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

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

                                                                                   ccache-swig(1)