The fact that queryPathInfo() is synchronous meant that we needed a
thread for every concurrent binary cache lookup, even though they end
up being handled by the same download thread. Requiring hundreds of
threads is not a good idea. So now there is an asynchronous version of
queryPathInfo() that takes a callback function to process the
result. Similarly, enqueueDownload() now takes a callback rather than
returning a future.
Thus, a command like
nix path-info --store https://cache.nixos.org/ -r /nix/store/slljrzwmpygy1daay14kjszsr9xix063-nixos-16.09beta231.dccf8c5
that returns 4941 paths now takes 1.87s using only 2 threads (the main
thread and the downloader thread). (This is with a prewarmed
CloudFront.)
It's a slight misnomer now because it actually limits *all* downloads,
not just binary cache lookups.
Also add a "enable-http2" option to allow disabling use of HTTP/2
(enabled by default).
The binary cache store can now use HTTP/2 to do lookups. This is much
more efficient than HTTP/1.1 due to multiplexing: we can issue many
requests in parallel over a single TCP connection. Thus it's no longer
necessary to use a bunch of concurrent TCP connections (25 by
default).
For example, downloading 802 .narinfo files from
https://cache.nixos.org/, using a single TCP connection, takes 11.8s
with HTTP/1.1, but only 0.61s with HTTP/2.
This did require a fairly substantial rewrite of the Downloader class
to use the curl multi interface, because otherwise curl wouldn't be
able to do multiplexing for us. As a bonus, we get connection reuse
even with HTTP/1.1. All downloads are now handled by a single worker
thread. Clients call Downloader::enqueueDownload() to tell the worker
thread to start the download, getting a std::future to the result.
This largely reverts c68e5913c7. Running
builds as root breaks "cp -p", since when running as root, "cp -p"
assumes that it can succesfully chown() files. But that's not actually
the case since the user namespace doesn't provide a complete uid
mapping. So it barfs with a fatal error message ("cp: failed to
preserve ownership for 'foo': Invalid argument").
This fixes an assertion failure in "assert(goal);" in
Worker::waitForInput() after a substitution goal is cancelled by the
termination of another goal. The problem was the line
//worker.childTerminated(shared_from_this()); // FIXME
in the SubstitutionGoal destructor. This was disabled because
shared_from_this() obviously doesn't work from a destructor. So we now
use a real pointer for object identity.
The inner lambda was returning a SQLite-internal char * rather than a
std::string, leading to Hydra errors liks
Caught exception in Hydra::Controller::Root->narinfo "path âø£â is not in the Nix store at /nix/store/6mvvyb8fgwj23miyal5mdr8ik4ixk15w-hydra-0.1.1234.abcdef/libexec/hydra/lib/Hydra/Controller/Root.pm line 352."
For example, you can now say:
configureFlags = "--prefix=${placeholder "out"} --includedir=${placeholder "dev"}";
The strings returned by the ‘placeholder’ builtin are replaced at
build time by the actual store paths corresponding to the specified
outputs.
Previously, you had to work around the inability to self-reference by doing stuff like:
preConfigure = ''
configureFlags+=" --prefix $out --includedir=$dev"
'';
or rely on ad-hoc variable interpolation semantics in Autoconf or Make
(e.g. --prefix=\$(out)), which doesn't always work.
This makes it easier to create a diverted store, i.e.
NIX_REMOTE="local?root=/tmp/root"
instead of
NIX_REMOTE="local?real=/tmp/root/nix/store&state=/tmp/root/nix/var/nix" NIX_LOG_DIR=/tmp/root/nix/var/log
For one particular NixOS configuration, this cut the runtime of
"nix-store -r --dry-run" from 6m51s to 3.4s. It also fixes a bug in
the size calculation that was causing certain paths to be counted
twice, e.g. before:
these paths will be fetched (1249.98 MiB download, 2995.74 MiB unpacked):
and after:
these paths will be fetched (1219.56 MiB download, 2862.17 MiB unpacked):
This way, all builds appear to have a uid/gid of 0 inside the
chroot. In the future, this may allow using programs like
systemd-nspawn inside builds, but that will require assigning a larger
UID/GID map to the build.
Issue #625.
This allows an unprivileged user to perform builds on a diverted store
(i.e. where the physical store location differs from the logical
location).
Example:
$ NIX_LOG_DIR=/tmp/log NIX_REMOTE="local?real=/tmp/store&state=/tmp/var" nix-build -E \
'with import <nixpkgs> {}; runCommand "foo" { buildInputs = [procps nettools]; } "id; ps; ifconfig; echo $out > $out"'
will do a build in the Nix store physically in /tmp/store but
logically in /nix/store (and thus using substituters for the latter).
