f90cache.1

.TH "f90cache" "1" "Aug 2015" "" ""

.SH "NAME"
f90cache \- a Fortran 90 compiler cache

.SH "VERSION"
0.96 \- Aug\&. 2015

.SH "SYNOPSIS"
f90cache [OPTION]
.PP
f90cache <compiler> [COMPILER OPTIONS]

.SH "DESCRIPTION"
f90cache is a compiler cache\&. It speeds up re-compilation of Fortran code
by caching previous compiles and detecting when the same compile is
being done again\&.

.SH "OPTIONS SUMMARY"
Here is a summary of the options to f90cache\&.
.PP

.nf
-s                show statistics summary
-z                zero statistics
-c                run a cache cleanup
-C                clear the cache completely
-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
.fi

.SH "OPTIONS"
These options only apply when you invoke f90cache as "f90cache"\&. 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\&.
.PP
.IP "\fB-h\fP"
Print a options summary page
.IP
.IP "\fB-s\fP"
Print the current statistics summary for the cache\&. The
statistics are stored spread across the subdirectories of the
cache\&. Using "f90cache -s" adds up the statistics across all
subdirectories and prints the totals\&.
.IP
.IP "\fB-z\fP"
Zero the cache statistics\&.
.IP
.IP "\fB-V\fP"
Print the f90cache version number
.IP
.IP "\fB-c\fP"
Clean the cache and re-calculate the cache file count and
size totals\&. Normally the -c option should not be necessary as f90cache
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\&.
.IP
.IP "\fB-C\fP"
Clear the entire cache, removing all cached files\&.
.IP
.IP "\fB-F maxfiles\fP"
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\&.
.IP
.IP "\fB-M maxsize\fP"
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\&.
.IP

.SH "INSTALLATION"
There are two ways to use f90cache\&. You can either prefix your compile
commands with "f90cache" or you can create a symbolic link between
f90cache and the names of your compilers\&. The first method is most
convenient if you just want to try out f90cache or wish to use it for
some specific projects\&. The second method is most useful for when you
wish to use f90cache for all your compiles\&.
.PP
To install for usage by the first method just copy f90cache to somewhere
in your path\&.
.PP
To install for the second method do something like this:

.nf
  cp f90cache /usr/local/bin/
  ln -s /usr/local/bin/f90cache /usr/local/bin/gfortran
.fi

This will work as long as /usr/local/bin comes before the path to gfortran\&.
After installing you may wish to run
"which gfortran" to make sure that the correct link is being used\&.
.PP
Note! Do not use a hard link, use a symbolic link\&.

.SH "EXTRA OPTIONS"
When run as a compiler front end "f90cache" usually just takes the same
command line options as the compiler you are using\&. The exceptions to this
rule are: \&(i\&) the option \&'--f90cache-skip\&'\&; that option can be used
to tell f90cache that the next option is definitely not an input filename, and
should be passed along to the compiler as-is\&. \&(ii\&) the option
\&'--f90cache-depmod\&'\&; that option takes one argument which must be
a precompiled Fortran module file which will be considered as a dependence
for the current source file\&.
.PP
Concerning the exception (i), the reason why this can be important is that
f90cache 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 f90cache uses in this parsing is that any string on the command
line that exists as a file is treated as an input file name (usually a
Fortran file)\&. By using \&'--f90cache-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\&.

.SH "ENVIRONMENT VARIABLES"
f90cache uses a number of environment variables to control operations\&. In
most cases you won\&'t need any of these as the defaults will be fine\&.
.PP
.IP
.IP "\fBF90CACHE_DIR\fP"
the F90CACHE_DIR environment variable specifies
where f90cache will keep its cached compiler output\&. The default is
"$HOME/\&.f90cache"\&.
.IP
.IP "\fBF90CACHE_TEMPDIR\fP"
the F90CACHE_TEMPDIR environment variable specifies
where f90cache will put temporary files\&. The default is the same as
F90CACHE_DIR\&. Note that the F90CACHE_TEMPDIR path must be on the same
filesystem as the F90CACHE_DIR path, so that renames of files between
the two directories can work\&.
.IP
.IP "\fBF90CACHE_LOGFILE\fP"
If you set the F90CACHE_LOGFILE environment
variable then f90cache will write some log information on cache hits
and misses in that file\&. This is useful for tracking down problems\&.
.IP
.IP "\fBF90CACHE_PATH\fP"
You can optionally set F90CACHE_PATH to a colon
separated path where f90cache will look for the real compilers\&. If you
don\&'t do this then f90cache will look for the first executable matching
the compiler name in the normal PATH that isn\&'t a symbolic link to
f90cache itself\&.
.IP
.IP "\fBF90CACHE_FC\fP"
You can optionally set F90CACHE_FC to force the name
of the compiler to use\&. If you don\&'t do this then f90cache works it out
from the command line\&.
.IP
.IP "\fBF90CACHE_PREFIX\fP"
This option adds a prefix to the command line
that f90cache runs when invoking the compiler\&.
.IP
.IP "\fBF90CACHE_DISABLE\fP"
If you set the environment variable
F90CACHE_DISABLE then f90cache will just call the real compiler,
bypassing the cache completely\&.
.IP
.IP "\fBF90CACHE_READONLY\fP"
the F90CACHE_READONLY environment variable
tells f90cache 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 F90CACHE_DIR is read-only, then you may find that you also need to
set F90CACHE_TEMPDIR as otherwise f90cache will fail to create the
temporary files\&.
.IP
.IP "\fBF90CACHE_FPP2\fP"
If you set the environment variable F90CACHE_FPP2
then f90cache 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 f90cache to be
used\&.
.IP
.IP "\fBF90CACHE_NOSTATS\fP"
If you set the environment variable
F90CACHE_NOSTATS then f90cache will not update the statistics files on
each compile\&.
.IP
.IP "\fBF90CACHE_NLEVELS\fP"
The environment variable F90CACHE_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\&.
.IP
.IP "\fBF90CACHE_HARDLINK\fP"
If you set the environment variable
F90CACHE_HARDLINK then f90cache 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\&.
.IP
.IP "\fBF90CACHE_RECACHE\fP"
This forces f90cache to not use any cached
results, even if it finds them\&. New results are still cached, but
existing cache entries are ignored\&.
.IP
.IP "\fBF90CACHE_UMASK\fP"
This sets the umask for f90cache 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\&.
.IP
.IP "\fBF90CACHE_HASHDIR\fP"
This tells f90cache 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
f90cache 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\&.
.IP

.SH "CACHE SIZE MANAGEMENT"
By default f90cache has a one gigabyte limit on the cache size and no
maximum number of files\&. You can set a different limit using the
"f90cache -M" and "f90cache -F" options, which set the size and number of
files limits\&.
.PP
When these limits are reached f90cache will reduce the cache to 20%
below the numbers you specified in order to avoid doing the cache
clean operation too often\&.

.SH "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\&. We detect
that it is the same code by forming a hash of:
.PP
.IP o
the source file given or (if applicable) the pre-processor output from
running the compiler with -E;
.IP o
some precompiled Fortran module files, whom the current source
file depends on (each module file must be given as an argument
of the '--f90cache-depmod' option);
.IP o
the command line options;
.IP o
the real compilers size and modification time\&.
.PP
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 f90cache is able to supply the correct compiler output (including
all warnings etc) from the cache\&.
.PP
Three kind of information are kept inside the cache:
.IP o
the object binary file;
.IP o
the precompiled module file (if any);
.IP o
the stderr output generated by the compiler\&.
.PP
f90cache 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 f90cache changes the output of your compiler then
please let me know\&.

.SH "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:
.PP
.IP o
Use the same \fBF90CACHE_DIR\fP environment variable setting
.IP o
Set the \fBF90CACHE_NOLINK\fP environment variable
.IP o
Make sure everyone sets the \fBF90CACHE_UMASK\fP environment variable
to 002, this ensures that cached files are accessible to everyone in
the group\&.
.IP o
Make sure that all users have write permission in the entire
cache directory (and that you trust all users of the shared cache)\&.
.IP 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 $F90CACHE_DIR -type d`" might
be useful for this\&.

.SH "HISTORY"
f90cache comes from ccache written by Andrew Tridgell\&. See the man page of
ccache for more information\&.
.PP

.SH "BUGS OR LIMITATIONS"
The full path of the working directory must not contain any blank character\&.

For GNU-GCC gfortran compilers, the actual name of the compiler must be
gfortran-x.y (e.g. \fBgfortran-4.8\fP, \fBgfortran-5.1\fP, ...). Releases
4.3 to 5.2 are supported. You may create symbolic links to fulfill this
requirement.

.SH "AUTHOR"
f90cache has been adapted from ccache by Édouard Canot (from 2009):
http://people\&.irisa\&.fr/Edouard\&.Canot
.PP
If you wish to report a problem or make a suggestion then please email
Edouard.Canot@irisa\&.fr