compiler cache and I wanted to remove some of the limitations of the
shell-script version.
-Installation
-------------
+Please see the manual page and documentation at
+http://ccache.samba.org/
-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:
-
- 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.
-
-Setting cache limits
---------------------
-
-Run "ccache -h" to see a list of options. The main ones you may wish
-to look at are "ccache -M" and "ccache -F" for setting the cache size
-limits.
-
-You can use "ccache -s" to look at the cache hit/miss statistics.
-
-Configuration
--------------
-
-Configuration of ccache is done via a number of environment variables
-and via ccache commands. 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_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_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 in the normal PATH that isn't a link
- to ccache itself.
-
-
- CCACHE_DISABLE
-
- If you set the environment variable CCACHE_DISABLE then ccache will
- just call the real compiler, bypassing the cache completely.
-
-
-Differences
-----------
-The biggest differences between Erik's compilercache script and ccache
-are:
-
-- ccache is written in C, which makes it a bit faster (calling out to
- external programs is mostly what slowed down the scripts).
-
-- ccache can automatically find the real compiler
-
-- ccache keeps statistics on hits/misses
-
-- ccache can do automatic cache management
-
-- ccache can cache compiler output that includes warnings. In many
- cases this gives ccache a much higher cache hit rate.
-
-- ccache can handle argument lists with spaces
-
-- compilercache does much smarter token unification using a C
- lexer. This means that reformatting of source code is much more
- likely to result in a cache miss with ccache than with
- compilercache. I may add this in future, although it is perhaps
- debatable whether the much slower parsing is worth it.
-
-Note however that ccache is a very new piece of code (as of March
-2002) whereas Erik's scripts have had a *lot* more testing.
-
-The overall speedup compared to compilercache is quite dramatic. For
-compiling rsync I get:
-
- normal build 20.74 seconds
-
- compilercache uncached 28.9 seconds
- compilercache cached 10.5 seconds
-
- ccache uncached 24.6 seconds
- ccache cached 4.6 seconds
-
-Cleaning 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.
-
-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:
-
- - the pre-processor output from running the compiler with -E
- - the command line options
- - the real compilers size and modification time
- - 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.
-
-===================
Andrew Tridgell
http://samba.org/~tridge/
bugs@ccache.samba.org
-March 2002
projects / thirdparty / ccache.git / commitdiff
