479e9172b3
Note that this will only work if the client has a very recent Nix
version (post 15e1b2c223), otherwise the
--option flag will just be ignored.
Fixes #50.
299 lines
10 KiB
Perl
Executable file
299 lines
10 KiB
Perl
Executable file
#! @perl@ -w @perlFlags@
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use Fcntl qw(:DEFAULT :flock);
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use English '-no_match_vars';
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use IO::Handle;
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use Nix::Config;
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use Nix::SSH qw/sshOpts openSSHConnection/;
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use Nix::CopyClosure;
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use Nix::Store;
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no warnings('once');
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# General operation:
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#
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# Try to find a free machine of type $neededSystem. We do this as
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# follows:
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# - We acquire an exclusive lock on $currentLoad/main-lock.
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# - For each machine $machine of type $neededSystem and for each $slot
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# less than the maximum load for that machine, we try to get an
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# exclusive lock on $currentLoad/$machine-$slot (without blocking).
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# If we get such a lock, we send "accept" to the caller. Otherwise,
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# we send "postpone" and exit.
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# - We release the exclusive lock on $currentLoad/main-lock.
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# - We perform the build on $neededSystem.
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# - We release the exclusive lock on $currentLoad/$machine-$slot.
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#
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# The nice thing about this scheme is that if we die prematurely, the
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# locks are released automatically.
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# Make sure that we don't get any SSH passphrase or host key popups -
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# if there is any problem it should fail, not do something
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# interactive.
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$ENV{"DISPLAY"} = "";
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$ENV{"SSH_ASKPASS"} = "";
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sub sendReply {
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my $reply = shift;
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print STDERR "# $reply\n";
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}
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sub all { $_ || return 0 for @_; 1 }
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# Initialisation.
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my $loadIncreased = 0;
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my ($localSystem, $maxSilentTime, $printBuildTrace, $buildTimeout) = @ARGV;
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my $currentLoad = $ENV{"NIX_CURRENT_LOAD"};
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my $conf = $ENV{"NIX_REMOTE_SYSTEMS"};
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sub openSlotLock {
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my ($machine, $slot) = @_;
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my $slotLockFn = "$currentLoad/" . (join '+', @{$machine->{systemTypes}}) . "-" . $machine->{hostName} . "-$slot";
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my $slotLock = new IO::Handle;
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sysopen $slotLock, "$slotLockFn", O_RDWR|O_CREAT, 0600 or die;
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return $slotLock;
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}
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# Read the list of machines.
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my @machines;
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if (defined $conf && -e $conf) {
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open CONF, "<$conf" or die;
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while (<CONF>) {
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chomp;
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s/\#.*$//g;
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next if /^\s*$/;
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my @tokens = split /\s/, $_;
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my @supportedFeatures = split(/,/, $tokens[5] || "");
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my @mandatoryFeatures = split(/,/, $tokens[6] || "");
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push @machines,
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{ hostName => $tokens[0]
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, systemTypes => [ split(/,/, $tokens[1]) ]
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, sshKeys => $tokens[2]
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, maxJobs => int($tokens[3])
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, speedFactor => 1.0 * (defined $tokens[4] ? int($tokens[4]) : 1)
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, supportedFeatures => [ @supportedFeatures, @mandatoryFeatures ]
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, mandatoryFeatures => [ @mandatoryFeatures ]
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, enabled => 1
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};
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}
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close CONF;
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}
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# Wait for the calling process to ask us whether we can build some derivation.
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my ($drvPath, $hostName, $slotLock);
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REQ: while (1) {
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$_ = <STDIN> || exit 0;
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(my $amWilling, my $neededSystem, $drvPath, my $requiredFeatures) = split;
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my @requiredFeatures = split /,/, $requiredFeatures;
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my $canBuildLocally = $amWilling && ($localSystem eq $neededSystem);
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if (!defined $currentLoad) {
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sendReply "decline";
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next;
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}
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# Acquire the exclusive lock on $currentLoad/main-lock.
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mkdir $currentLoad, 0777 or die unless -d $currentLoad;
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my $mainLock = "$currentLoad/main-lock";
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sysopen MAINLOCK, "$mainLock", O_RDWR|O_CREAT, 0600 or die;
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flock(MAINLOCK, LOCK_EX) or die;
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while (1) {
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# Find all machine that can execute this build, i.e., that
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# support builds for the given platform and features, and are
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# not at their job limit.
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my $rightType = 0;
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my @available = ();
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LOOP: foreach my $cur (@machines) {
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if ($cur->{enabled}
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&& (grep { $neededSystem eq $_ } @{$cur->{systemTypes}})
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&& all(map { my $f = $_; 0 != grep { $f eq $_ } @{$cur->{supportedFeatures}} } (@requiredFeatures, @mandatoryFeatures))
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&& all(map { my $f = $_; 0 != grep { $f eq $_ } @requiredFeatures } @{$cur->{mandatoryFeatures}})
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)
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{
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$rightType = 1;
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# We have a machine of the right type. Determine the load on
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# the machine.
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my $slot = 0;
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my $load = 0;
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my $free;
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while ($slot < $cur->{maxJobs}) {
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my $slotLock = openSlotLock($cur, $slot);
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if (flock($slotLock, LOCK_EX | LOCK_NB)) {
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$free = $slot unless defined $free;
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flock($slotLock, LOCK_UN) or die;
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} else {
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$load++;
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}
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close $slotLock;
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$slot++;
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}
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push @available, { machine => $cur, load => $load, free => $free }
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if $load < $cur->{maxJobs};
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}
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}
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if (defined $ENV{NIX_DEBUG_HOOK}) {
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print STDERR "load on " . $_->{machine}->{hostName} . " = " . $_->{load} . "\n"
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foreach @available;
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}
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# Didn't find any available machine? Then decline or postpone.
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if (scalar @available == 0) {
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# Postpone if we have a machine of the right type, except
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# if the local system can and wants to do the build.
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if ($rightType && !$canBuildLocally) {
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sendReply "postpone";
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} else {
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sendReply "decline";
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}
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close MAINLOCK;
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next REQ;
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}
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# Prioritise the available machines as follows:
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# - First by load divided by speed factor, rounded to the nearest
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# integer. This causes fast machines to be preferred over slow
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# machines with similar loads.
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# - Then by speed factor.
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# - Finally by load.
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sub lf { my $x = shift; return int($x->{load} / $x->{machine}->{speedFactor} + 0.4999); }
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@available = sort
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{ lf($a) <=> lf($b)
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|| $b->{machine}->{speedFactor} <=> $a->{machine}->{speedFactor}
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|| $a->{load} <=> $b->{load}
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} @available;
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# Select the best available machine and lock a free slot.
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my $selected = $available[0];
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my $machine = $selected->{machine};
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$slotLock = openSlotLock($machine, $selected->{free});
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flock($slotLock, LOCK_EX | LOCK_NB) or die;
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utime undef, undef, $slotLock;
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close MAINLOCK;
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# Connect to the selected machine.
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@sshOpts = ("-i", $machine->{sshKeys}, "-x");
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$hostName = $machine->{hostName};
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last REQ if openSSHConnection $hostName;
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warn "unable to open SSH connection to $hostName, trying other available machines...\n";
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$machine->{enabled} = 0;
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}
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}
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# Tell Nix we've accepted the build.
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sendReply "accept";
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my @inputs = split /\s/, readline(STDIN);
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my @outputs = split /\s/, readline(STDIN);
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print STDERR "building `$drvPath' on `$hostName'\n";
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print STDERR "@ build-remote $drvPath $hostName\n" if $printBuildTrace;
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my $maybeSign = "";
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$maybeSign = "--sign" if -e "$Nix::Config::confDir/signing-key.sec";
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# Register the derivation as a temporary GC root. Note that $PPID is
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# the PID of the remote SSH process, which, due to the use of a
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# persistant SSH connection, should be the same across all remote
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# command invocations for this session.
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my $rootsDir = "@localstatedir@/nix/gcroots/tmp";
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system("ssh $hostName @sshOpts 'mkdir -m 1777 -p $rootsDir; ln -sfn $drvPath $rootsDir/\$PPID.drv'");
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sub removeRoots {
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system("ssh $hostName @sshOpts 'rm -f $rootsDir/\$PPID.drv $rootsDir/\$PPID.out'");
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}
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# Copy the derivation and its dependencies to the build machine. This
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# is guarded by an exclusive lock per machine to prevent multiple
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# build-remote instances from copying to a machine simultaneously.
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# That's undesirable because we may end up with N instances uploading
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# the same missing path simultaneously, causing the effective network
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# bandwidth and target disk speed to be divided by N.
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my $uploadLock = "$currentLoad/$hostName.upload-lock";
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sysopen UPLOADLOCK, "$uploadLock", O_RDWR|O_CREAT, 0600 or die;
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eval {
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local $SIG{ALRM} = sub { die "alarm\n" };
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# Don't wait forever, so that a process that gets stuck while
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# holding the lock doesn't block everybody else indefinitely.
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# It's safe to continue after a timeout, just (potentially)
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# inefficient.
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alarm 15 * 60;
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flock(UPLOADLOCK, LOCK_EX);
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alarm 0;
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};
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if ($@) {
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die unless $@ eq "alarm\n";
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print STDERR "somebody is hogging $uploadLock, continuing...\n";
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unlink $uploadLock;
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}
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Nix::CopyClosure::copyTo($hostName, [ @sshOpts ], [ $drvPath, @inputs ], "", "", 0, 0, $maybeSign ne "", "");
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close UPLOADLOCK;
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# Perform the build.
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my $buildFlags =
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"--max-silent-time $maxSilentTime --option build-timeout $buildTimeout "
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. "--fallback --add-root $rootsDir/\$PPID.out --option verbosity 0";
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# We let the remote side kill its process group when the connection is
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# closed unexpectedly. This is necessary to ensure that no processes
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# are left running on the remote system if the local Nix process is
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# killed. (SSH itself doesn't kill child processes if the connection
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# is interrupted unless the `-tt' flag is used to force a pseudo-tty,
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# in which case every child receives SIGHUP; however, `-tt' doesn't
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# work on some platforms when connection sharing is used.)
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pipe STDIN, DUMMY; # make sure we have a readable STDIN
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if (system("exec ssh $hostName @sshOpts '(read; kill -INT -\$\$) <&0 & nix-store -r $drvPath $buildFlags > /dev/null' 2>&4") != 0) {
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# Note that if we get exit code 100 from `nix-store -r', it
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# denotes a permanent build failure (as opposed to an SSH problem
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# or a temporary Nix problem). We propagate this to the caller to
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# allow it to distinguish between transient and permanent
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# failures.
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my $res = $? >> 8;
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print STDERR "build of `$drvPath' on `$hostName' failed with exit code $res\n";
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removeRoots;
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exit $res;
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}
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#print "build of `$drvPath' on `$hostName' succeeded\n";
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# Copy the output from the build machine.
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foreach my $output (@outputs) {
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my $maybeSignRemote = "";
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$maybeSignRemote = "--sign" if $UID != 0;
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next if isValidPath($output);
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system("exec ssh $hostName @sshOpts 'nix-store --export $maybeSignRemote $output'" .
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"| NIX_HELD_LOCKS=$output @bindir@/nix-store --import > /dev/null") == 0
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or die "cannot copy $output from $hostName: $?";
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}
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# Get rid of the temporary GC roots.
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removeRoots;
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