On multi-developer software projects, you can sometimes speed up every developer's builds a lot by allowing them to share the derived files that they build. SCons makes this easy, as well as reliable.
To enable sharing of derived files,
in any SConscript file:
Note that the directory you specify must already exist and be readable and writable by all developers who will be sharing derived files. It should also be in some central location that all builds will be able to access. In environments where developers are using separate systems (like individual workstations) for builds, this directory would typically be on a shared or NFS-mounted file system.
Here's what happens:
When a build has a
every time a file is built,
it is stored in the shared cache directory
along with its MD5 build signature.
On subsequent builds,
before an action is invoked to build a file,
SCons will check the shared cache directory
to see if a file with the exact same build
signature already exists.
If so, the derived file will not be built locally,
but will be copied into the local build directory
from the shared cache directory,
% scons -Q cc -o hello.o -c hello.c cc -o hello hello.o % scons -Q -c Removed hello.o Removed hello % scons -Q Retrieved `hello.o' from cache Retrieved `hello' from cache
Note that the
CacheDir feature still calculates
MD5 build sigantures for the shared cache file names
even if you configure SCons to use timestamps
to decide if files are up to date.
(See the Chapter 6
chapter for information about the
CacheDir may reduce or eliminate any
potential performance improvements
from using timestamps for up-to-date decisions.
Actually, the MD5 signature is used as the name of the file in the shared cache directory in which the contents are stored.