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authorEelco Dolstra <e.dolstra@tudelft.nl>2011-12-21T18·59+0000
committerEelco Dolstra <e.dolstra@tudelft.nl>2011-12-21T18·59+0000
commit69d6f0936a59da5cc35040407f4b667437d61add (patch)
tree359468ac775b4f2851a806f7e00d1838bd5c5650 /scripts
parent38776198880d06dc6af0fbdfa7cb2c053000112a (diff)
* Use a lock to ensure that only one build-remote instance can copy a
  closure to a given machine at the same time.  This prevents the case
  where multiple instances try to copy the same missing store path to
  the target machine, which is very wasteful.

Diffstat (limited to 'scripts')
-rwxr-xr-xscripts/build-remote.pl.in11
1 files changed, 10 insertions, 1 deletions
diff --git a/scripts/build-remote.pl.in b/scripts/build-remote.pl.in
index c805d6740ef3..6a6515756163 100755
--- a/scripts/build-remote.pl.in
+++ b/scripts/build-remote.pl.in
@@ -225,8 +225,17 @@ sub removeRoots {
 }
 
 
-# Copy the derivation and its dependencies to the build machine.
+# Copy the derivation and its dependencies to the build machine.  This
+# is guarded by an exclusive lock per machine to prevent multiple
+# build-remote instances from copying to a machine simultaneously.
+# That's undesirable because we may end up with N instances uploading
+# the same missing path simultaneously, causing the effective network
+# bandwidth and target disk speed to be divided by N.
+my $uploadLock = "$currentLoad/$hostName.upload-lock";
+open MAINLOCK, ">>$uploadLock" or die;
+flock(MAINLOCK, LOCK_EX) or die;
 Nix::CopyClosure::copyTo($hostName, [ @sshOpts ], [ $drvPath, @inputs ], "", "", 0, 0, $maybeSign ne "");
+close MAINLOCK;
 
 
 # Perform the build.