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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
      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.





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      -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++



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 ccache-swig(1)                                               ccache-swig(1)




        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 wont 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.




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      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 dont do
           this then ccache will look for the first executable matching the
           compiler name in the normal PATH that isnt 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 dont 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



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           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



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           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 doesnt 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.



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 ccache-swig(1)                                               ccache-swig(1)






      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.





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 ccache-swig(1)                                               ccache-swig(1)




      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 files 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 Eriks scripts.



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 ccache-swig(1)                                               ccache-swig(1)




      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 Eriks 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.




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