ccache/ccache.yo

mailto(bugs@ccache.samba.org)
manpage(ccache)(1)(April 2002)()()
manpagename(ccache)(a fast compiler cache)
manpagesynopsis()

ccache [OPTION]

ccache <compiler> [COMPILER OPTIONS]

<compiler> [COMPILER OPTIONS]

manpagedescription()

ccache is a compiler cache. It speeds up re-compilation of C/C++ code 
by caching previous compiles and detecting when the same compile is
being done again.

manpagesection(OPTIONS SUMMARY)

Here is a summary of the options to ccache.

verb(
-s                      show statistics summary
-z                      zero statistics
-c                      run a cache cleanup
-F <maxfiles>           set maximum files in cache
-M <maxsize>            set maximum size of cache (use G, M or K)
-h                      this help page
-V                      print version number
)

manpageoptions()

These options only apply when you invoke ccache as "ccache". 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.

startdit()
dit(bf(-h)) Print a options summary page

dit(bf(-s)) Print the current statistics summary for the cache. The
statistics are stored spread across the subdirectories of the
cache. Using "ccache -s" adds up the statistics across all
subdirectories and prints the totals.

dit(bf(-z)) Zero the cache statistics. 

dit(bf(-V)) Print the ccache version number

dit(bf(-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.

dit(bf(-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.

dit(bf(-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.

enddit()

manpagesection(INSTALLATION)

There are two ways to use ccache. You can either prefix your compile
commands with "ccache" or you can create a symbolic link between
ccache 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 to somewhere
in your path. 

To install for the second method do something like this:
verb(
  cp ccache /usr/local/bin/
  ln -s /usr/local/bin/ccache /usr/local/bin/gcc
  ln -s /usr/local/bin/ccache /usr/local/bin/cc
)
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.

manpagesection(ENVIRONMENT VARIABLES)

ccache used a number of environment variables to control operation. In
most cases you won't need any of these as the defaults will be fine.

startdit()

dit(bf(CCACHE_DIR)) the CCACHE_DIR environment variable specifies
where ccache will keep its cached compiler output. The default is
"$HOME/.ccache".

dit(bf(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.

dit(bf(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.

dit(bf(CCACHE_DISABLE)) If you set the environment variable
CCACHE_DISABLE then ccache will just call the real compiler,
bypassing the cache completely.

dit(bf(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.

dit(bf(CCACHE_NOSTATS)) If you set the environment variable
CCACHE_NOSTATS then ccache will not update the statistics files on
each compile.

dit(bf(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. 

dit(bf(CCACHE_NOLINK)) If you set the environment variable
CCACHE_NOLINK then ccache will not use hard links from the cache
directory when creating the compiler output and will do a file copy
instead. The main reason for setting this option is to avoid the
update of the modification time on object files that are the result of
the same compilation in a different directory.

dit(bf(CCACHE_NOUNIFY)) If you set the environment variable
CCACHE_NOUNIFY then ccache will not use the C/C++ unifier when hashing
the pre-processor output. The unifier is slower than a normal hash, so
setting this environment variable gains a little bit of speed, but it
means that ccache can't take advantage of not recompiling when the
changes to the source code consist of reformatting only. Note that
using CCACHE_NOUNIFY changes the hash, so cached compiles with
CCACHE_NOUNIFY set cannot be used when CCACHE_NOUNIFY is not set and
vice versa.

enddit()

manpagesection(CACHE SIZE MANAGEMENT)

By default ccache has no limit on the cache size. You can set a 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.

manpagesection(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:

itemize(
  it() the pre-processor output from running the compiler with -E
  it() the command line options
  it() the real compilers size and modification time
  it() 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.

manpagesection(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 
url(http://www.erikyyy.de/compilercache/)(http://www.erikyyy.de/compilercache/)
for the Erik's scripts.

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.

manpagesection(DIFFERENCES FROM COMPILERCACHE)

The biggest differences between Erik's compilercache script and ccache
are:
itemize(
it() ccache is written in C, which makes it a bit faster (calling out to
  external programs is mostly what slowed down the scripts).
it() ccache can automatically find the real compiler
it() ccache keeps statistics on hits/misses
it() ccache can do automatic cache management
it() ccache can cache compiler output that includes warnings. In many
  cases this gives ccache a much higher cache hit rate.
it() ccache can handle a much wider ranger of compiler options
it() ccache avoids a double call to cpp on a cache miss
)

manpagesection(CREDITS)

Thanks to the following people for their contributions to ccache
itemize(
 it() Erik Thiele for the original compilercache script
 it() Luciano Rocha for the idea of compiling the pre-processor output
 to avoid a 2nd cpp pass
 it() Paul Russell for many suggestions and the debian packaging
)

manpageauthor()

ccache was written by Andrew Tridgell
url(http://samba.org/~tridge/)(http://samba.org/~tridge/)

If you wish to report a problem or make a suggestion then please email
bugs@ccache.samba.org

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