* Register GC roots properly.

src/c/hydra_eval_jobs.cc

@@ -19,6 +19,9 @@ void printHelp()
 }
 
 
+static Path gcRootsDir;
+
+
 Expr evalAttr(EvalState & state, Expr e)
 {
     return e ? evalExpr(state, e) : e;
@@ -97,12 +100,12 @@ static void findJobsWrapped(EvalState & state, XMLWriter & doc,
         
         if (getDerivation(state, e, drv)) {
             XMLAttrs xmlAttrs;
-            Path outPath, drvPath;
+            Path drvPath;
 
             xmlAttrs["jobName"] = attrPath;
             xmlAttrs["nixName"] = drv.name;
             xmlAttrs["system"] = drv.system;
-            xmlAttrs["drvPath"] = drv.queryDrvPath(state);
+            xmlAttrs["drvPath"] = drvPath = drv.queryDrvPath(state);
             xmlAttrs["outPath"] = drv.queryOutPath(state);
             xmlAttrs["description"] = drv.queryMetaInfo(state, "description");
             xmlAttrs["longDescription"] = drv.queryMetaInfo(state, "longDescription");
@@ -110,6 +113,12 @@ static void findJobsWrapped(EvalState & state, XMLWriter & doc,
             xmlAttrs["homepage"] = drv.queryMetaInfo(state, "homepage");
             xmlAttrs["schedulingPriority"] = drv.queryMetaInfo(state, "schedulingPriority");
         
+            /* Register the derivation as a GC root.  !!! This
+               registers roots for jobs that we may have already
+               done. */
+            Path root = gcRootsDir + "/" + baseNameOf(drvPath);
+            if (!pathExists(root)) addPermRoot(drvPath, root, false);
+            
             XMLOpenElement _(doc, "job", xmlAttrs);
             showArgsUsed(doc, argsUsed);
         }
@@ -170,6 +179,10 @@ void run(Strings args)
                     ? (ATermList) autoArgs.get(toATerm(name))
                     : ATempty, e));
         }
+        else if (arg == "--gc-roots-dir") {
+            if (i == args.end()) throw UsageError("missing argument");
+            gcRootsDir = *i++;
+        }
         else if (arg[0] == '-')
             throw UsageError(format("unknown flag `%1%'") % arg);
         else
@@ -178,6 +191,8 @@ void run(Strings args)
 
     if (releaseExpr == "") throw UsageError("no expression specified");
     
+    if (gcRootsDir == "") throw UsageError("--gc-roots-dir not specified");
+    
     store = openStore();
 
     Expr e = parseExprFromFile(state, releaseExpr);

src/lib/Hydra/Helper/Nix.pm

@@ -9,7 +9,7 @@ our @ISA = qw(Exporter);
 our @EXPORT = qw(
     isValidPath queryPathInfo
     getHydraPath getHydraDBPath openHydraDB
-    registerRoot getGCRootsDir
+    registerRoot getGCRootsDir gcRootFor
     getPrimaryBuildsForReleaseSet getRelease getLatestSuccessfulRelease );
 
 
@@ -80,22 +80,26 @@ sub openHydraDB {
 
 sub getGCRootsDir {
     die unless defined $ENV{LOGNAME};
-    return "/nix/var/nix/gcroots/per-user/$ENV{LOGNAME}/hydra-roots";
+    my $dir = "/nix/var/nix/gcroots/per-user/$ENV{LOGNAME}/hydra-roots";
+    mkpath $dir if !-e $dir;
+    return $dir;
+}
+
+
+sub gcRootFor {
+    my ($path) = @_;
+    return getGCRootsDir . basename $path;
 }
 
 
 sub registerRoot {
     my ($path) = @_;
     
-    my $gcRootsDir = getGCRootsDir;
+    my $link = gcRootFor $path;
-    
-    mkpath($gcRootsDir) if !-e $gcRootsDir;
-
-    my $link = "$gcRootsDir/" . basename $path;
     
     if (!-l $link) {
         symlink($path, $link)
-            or die "cannot create symlink in $gcRootsDir to $path";
+            or die "cannot create GC root `$link' to `$path'";
     }
 }
 

src/script/hydra_build.pl

@@ -28,8 +28,6 @@ sub doBuild {
     my $failedDepBuild;
     my $failedDepStepNr;
     
-    registerRoot $outPath;
-    
     if (!isValidPath($outPath)) {
         $isCachedBuild = 0;
 
@@ -75,7 +73,8 @@ sub doBuild {
         # to get notifications about specific build steps, the
         # associated log files, etc.
         my $cmd = "nix-store --max-silent-time 1800 --keep-going --no-build-output " .
-            "--log-type flat --print-build-trace --realise $drvPath 2>&1";
+            "--log-type flat --print-build-trace --realise $drvPath " .
+            "--add-root " . gcRootFor $outPath . " 2>&1";
 
         my $buildStepNr = 1;
         

src/script/hydra_scheduler.pl

@@ -267,9 +267,6 @@ sub checkJob {
                 , sha256hash => $input->{sha256hash}
                 });
         }
-        
-        # !!! this should really by done by nix-instantiate to prevent a GC race.
-        registerRoot $drvPath;
     });
 };
 
@@ -330,9 +327,12 @@ sub checkJobSet {
     $nixExprPath .= "/" . $jobset->nixexprpath;
 
     (my $res, my $jobsXml, my $stderr) = captureStdoutStderr(
-        "hydra_eval_jobs", $nixExprPath, inputsToArgs($inputInfo));
+        "hydra_eval_jobs", $nixExprPath, "--gc-roots-dir", getGCRootsDir,
+        inputsToArgs($inputInfo));
     die "cannot evaluate the Nix expression containing the jobs:\n$stderr" unless $res;
 
+    print STDERR "$stderr";
+
     my $jobs = XMLin($jobsXml,
                      ForceArray => ['error', 'job', 'arg'],
                      KeyAttr => [],

src/script/hydra_update_gc_roots.pl

@@ -83,14 +83,14 @@ my @buildsToKeep = $db->resultset('Builds')->search({finished => 1, keep => 1},
 keepBuild $_ foreach @buildsToKeep;
 
 
-# For scheduled builds, we register the derivation and the output as a GC root.
+# For scheduled builds, we register the derivation as a GC root.
 print STDERR "*** looking for scheduled builds\n";
 foreach my $build ($db->resultset('Builds')->search({finished => 0}, {join => 'schedulingInfo'})) {
     if (isValidPath($build->drvpath)) {
         print STDERR "keeping scheduled build ", $build->id, " (",
             strftime("%Y-%m-%d %H:%M:%S", localtime($build->timestamp)), ")\n";
         registerRoot $build->drvpath;
-        registerRoot $build->outpath;
+        registerRoot $build->outpath if -e $build->outpath;
     } else {
         print STDERR "warning: derivation ", $build->drvpath, " has disappeared\n";
     }