in parallel. Hooks are more efficient: locks on output paths are
only acquired when the hook says that it is willing to accept a
build job. Hooks now work in two phases. First, they should first
tell Nix whether they are willing to accept a job. Nix guarantuees
that no two hooks will ever be in the first phase at the same time
(this simplifies the implementation of hooks, since they don't have
to perform locking (?)). Second, if they accept a job, they are
then responsible for building it (on the remote system), and copying
the result back. These can be run in parallel with other hooks and
locally executed jobs.
The implementation is a bit messy right now, though.
* The directory `distributed' shows a (hacky) example of a hook that
distributes build jobs over a set of machines listed in a
configuration file.
parallel as possible (similar to GNU Make's `-j' switch). This is
useful on SMP systems, but it is especially useful for doing builds
on multiple machines. The idea is that a large derivation is
initiated on one master machine, which then distributes
sub-derivations to any number of slave machines. This should not
happen synchronously or in lock-step, so the master must be capable
of dealing with multiple parallel build jobs. We now have the
infrastructure to support this.
TODO: substitutes are currently broken.
This is because the contents of these symlinks are not incorporated
into the hashes of derivations, and could therefore cause a mismatch
between the build system and the target system. E.g., if
`/nix/store' is a symlink to `/data/nix/store', then a builder could
expand this path and store the result. If on the target system
`/nix/store' is not a symlink, or is a symlink that points somewhere
else, we have a dangling pointer.
The trigger for this change is that gcc 3.3.3 does exactly that (it
applies realpath() to some files, such as libraries, which causes
our impurity checker to bail out.)
An annoying side-effect of this change is that it makes it harder to
move the Nix store to a different file system. On Linux, bind
mounts can be used instead of symlink for this purpose (e.g., `mount
-o bind /data/nix/store /nix/store').
writes to stderr:
- `pretty': the old nested style (default)
- `escapes': uses escape codes to indicate nesting and message
level; can be processed using `log2xml'
- `flat': just plain text, no nesting
These can be set using `--log-type TYPE' or the NIX_LOG_TYPE
environment variable.
* Do not create stuff in localstatedir when doing `make install'
(since we may not have write access). In general, installation of
constant code/data should be separate from the initialisation of
mutable state.
chroot() environment.
* A operation `--validpath' to register path validity. Useful for
bootstrapping in a pure Nix environment.
* Safety checks: ensure that files involved in store operations are in
the store.
Nix. This is to prevent Berkeley DB from becoming wedged.
Unfortunately it is not possible to throw C++ exceptions from a
signal handler. In fact, you can't do much of anything except
change variables of type `volatile sig_atomic_t'. So we set an
interrupt flag in the signal handler and check it at various
strategic locations in the code (by calling checkInterrupt()).
Since this is unlikely to cover all cases (e.g., (semi-)infinite
loops), sometimes SIGTERM may now be required to kill Nix.
turned out to be a huge performance bottleneck (the text to printed
would always be evaluated, even when it was above the verbosity
level). This reduces fix-ng execution time by over 50%.
gprof(1) is very useful. :-)
