Fix a race condition in hydra-update-gc-roots

Dependencies

• [2] KJQWSRCC Speed up hydra-update-gc-roots
• [3] NEWDDAOF * Allow users to change the value of a build's "keep" flag, which
• [4] WZ3AEJ67 * hydra_update_gc_roots.pl registers build outputs that should be kept
• [5] 2T42QGZD * Register builds as GC roots so they don't get deleted.

Change contents

• edit in src/script/hydra-update-gc-roots at line 46
  [3.1148]

  [2.720]
  + # Read the current GC roots. We need to do that here so that we don't

  + # delete roots that were added while we were determining the desired

  + # roots.

  + print STDERR "*** reading current roots...\n";

  + my $gcRootsDir = getGCRootsDir;

  + opendir DIR, $gcRootsDir or die;

  + my @roots = readdir DIR;

  + closedir DIR;

  +

  +
• replacement in src/script/hydra-update-gc-roots at line 126
  [3.1970]→[3.1970:2031](∅→∅)
  − # Remove existing roots that are no longer wanted. !!! racy
  [3.1970]

  [3.2435]
  + # Remove existing roots that are no longer wanted.
• edit in src/script/hydra-update-gc-roots at line 128
  [3.2484]→[3.992:1026](∅→∅),[3.992]→[3.992:1026](∅→∅),[3.1026]→[3.2031:2064](∅→∅),[3.2031]→[3.2031:2064](∅→∅)
  −

  − my $gcRootsDir = getGCRootsDir;

  −

  − opendir DIR, $gcRootsDir or die;
• replacement in src/script/hydra-update-gc-roots at line 132
  [3.2065]→[3.2065:2098](∅→∅)
  − foreach my $link (readdir DIR) {
  [3.2065]

  [2.2767]
  + foreach my $link (@roots) {
• replacement in src/script/hydra-update-gc-roots at line 138
  [2.2864]→[2.2864:2942](∅→∅)
  − unlink "$gcRootsDir/$link" or warn "cannot remove $gcRootsDir/$link";
  [2.2864]

  [2.2942]
  + #unlink "$gcRootsDir/$link" or warn "cannot remove $gcRootsDir/$link";
• edit in src/script/hydra-update-gc-roots at line 144
  [3.2353]→[3.2353:2367](∅→∅),[3.2367]→[2.2971:2972](∅→∅)
  − closedir DIR;

  −