* Fix and simplify the garbage collector (it's still not concurrent,
though). In particular it's now much easier to register a GC root. Just place a symlink to whatever store path it is that you want to keep in /nix/var/nix/gcroots.
This commit is contained in:
Eelco Dolstra
parent
59682e6188
commit
c505702265
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@ -23,7 +23,7 @@ for i in "$@"; do
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for j in $storeExprs; do
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echo "store expression is $j" >&2
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done
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outPaths=$(@bindir@/nix-store -qnfv $extraArgs $storeExprs)
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outPaths=$(@bindir@/nix-store -rv $extraArgs $storeExprs)
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for j in $outPaths; do
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echo "$j"
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if test -z "$noLink"; then
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@ -9,7 +9,6 @@ my $storeDir = "@storedir@";
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my %alive;
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my $gcOper = "--delete";
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my $minAge = 0;
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my @roots = ();
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@ -20,33 +19,11 @@ for (my $i = 0; $i < scalar @ARGV; $i++) {
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if ($arg eq "--delete" || $arg eq "--print-live" || $arg eq "--print-dead") {
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$gcOper = $arg;
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}
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elsif ($arg eq "--min-age") {
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$i++;
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$minAge = undef;
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$minAge = $ARGV[$i];
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die "invalid minimum age" unless defined $minAge && $minAge =~ /^\d*$/;
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}
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else { die "unknown argument `$arg'" };
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}
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# Read all GC roots from the given file.
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sub readRoots {
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my $fileName = shift;
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open ROOT, "<$fileName" or die "cannot open `$fileName': $!";
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while (<ROOT>) {
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chomp;
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foreach my $root (split ' ') {
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die "bad root `$root' in file `$fileName'"
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unless $root =~ /^\S+$/;
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push @roots, $root;
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}
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}
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close ROOT;
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}
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# Recursively finds all *.gcroot files in the given directory.
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# Recursively finds all symlinks to the store in the given directory.
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sub findRoots;
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sub findRoots {
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my $followSymlinks = shift;
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@ -58,14 +35,26 @@ sub findRoots {
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foreach my $name (@names) {
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next if $name eq "." || $name eq "..";
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$name = $dir . "/" . $name;
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if ($name =~ /.gcroot$/ && -f $name) {
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readRoots $name;
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}
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elsif (-d $name) {
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if ($followSymlinks || !-l $name) {
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findRoots 0, $name;
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my $path = $dir . "/" . $name;
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if (-l $path) {
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my $target = readlink $path
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or die "cannot read symlink `$path': $!";
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if (substr($target, 0, length $storeDir) eq $storeDir) {
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# We're only interested in the store-level part.
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$target = substr($target, length $storeDir);
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$target = "$storeDir/$target";
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push @roots, $target;
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}
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elsif ($followSymlinks && -d $path) {
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findRoots 0, $path;
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}
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}
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elsif (-d $path) {
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findRoots $followSymlinks, $path;
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}
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}
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@ -77,7 +66,7 @@ findRoots 1, $rootsDir;
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# Run the collector with the roots we found.
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my $pid = open2(">&1", \*WRITE, "@bindir@/nix-store --gc $gcOper --min-age $minAge")
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my $pid = open2(">&1", \*WRITE, "@bindir@/nix-store --gc $gcOper")
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or die "cannot run `nix-store --gc'";
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foreach my $root (@roots) {
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@ -458,7 +458,7 @@ void DerivationGoal::haveStoreExpr()
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i != invalidOutputs.end(); ++i)
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/* Don't bother creating a substitution goal if there are no
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substitutes. */
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if (querySubstitutes(*i).size() > 0)
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if (querySubstitutes(noTxn, *i).size() > 0)
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addWaitee(worker.makeSubstitutionGoal(*i));
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if (waitees.empty()) /* to prevent hang (no wake-up event) */
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@ -1315,7 +1315,7 @@ void SubstitutionGoal::init()
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}
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/* Read the substitutes. */
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subs = querySubstitutes(storePath);
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subs = querySubstitutes(noTxn, storePath);
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/* To maintain the closure invairant, we first have to realise the
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paths referenced by this one. */
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@ -1,12 +1,68 @@
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#include "globals.hh"
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#include "gc.hh"
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#include "build.hh"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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void collectGarbage(const PathSet & roots, GCAction action,
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PathSet & result)
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{
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result.clear();
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/* !!! TODO: Acquire an exclusive lock on the gcroots directory.
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This prevents the set of live paths from increasing after this
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point. */
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/* Determine the live paths which is just the closure of the
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roots under the `references' relation. */
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PathSet livePaths;
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for (PathSet::const_iterator i = roots.begin(); i != roots.end(); ++i)
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computeFSClosure(canonPath(*i), livePaths);
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if (action == gcReturnLive) {
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result = livePaths;
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return;
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}
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/* !!! TODO: Try to acquire (without blocking) exclusive locks on
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the files in the `pending' directory. Delete all files for
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which we managed to acquire such a lock (since if we could get
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such a lock, that means that the process that owned the file
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has died). */
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/* !!! TODO: Acquire shared locks on all files in the pending
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directories. This prevents the set of pending paths from
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increasing while we are garbage-collecting. Read the set of
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pending paths from those files. */
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/* Read the Nix store directory to find all currently existing
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paths. */
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Strings storeNames = readDirectory(nixStore);
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for (Strings::iterator i = storeNames.begin(); i != storeNames.end(); ++i) {
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Path path = canonPath(nixStore + "/" + *i);
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if (livePaths.find(path) != livePaths.end()) {
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debug(format("live path `%1%'") % path);
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continue;
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}
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debug(format("dead path `%1%'") % path);
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result.insert(path);
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if (action == gcDeleteDead) {
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printMsg(lvlInfo, format("deleting `%1%'") % path);
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deleteFromStore(path);
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}
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}
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}
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#if 0
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void followLivePaths(Path nePath, PathSet & live)
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{
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@ -3,24 +3,15 @@
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#include "util.hh"
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/* Garbage collector operation. */
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typedef enum { gcReturnLive, gcReturnDead, gcDeleteDead } GCAction;
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/* Determine the set of "live" store paths, given a set of root store
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expressions. The live store paths are those that are reachable
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from the roots. The roots are reachable by definition. Any path
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mentioned in a reachable store expression is also reachable. If a
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derivation store expression is reachable, then its successor (if it
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exists) if also reachable. It is not an error for store
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expressions not to exist (since this can happen on derivation store
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expressions, for instance, due to the substitute mechanism), but
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successor links are followed even for non-existant derivations. */
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PathSet findLivePaths(const Paths & roots);
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/* Given a set of "live" store paths, determine the set of "dead"
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store paths (which are simply all store paths that are not in the
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live set). The value `minAge' specifies the minimum age in seconds
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for an unreachable file to be considered dead (0 meaning that any
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unreachable file is dead). */
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PathSet findDeadPaths(const PathSet & live, time_t minAge);
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/* If `action' is set to `soReturnLive', return the set of paths
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reachable from (i.e. in the closure of) the specified roots. If
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`action' is `soReturnDead', return the set of paths not reachable
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from the roots. If `action' is `soDeleteDead', actually delete the
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latter set. */
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void collectGarbage(const PathSet & roots, GCAction action,
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PathSet & result);
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#endif /* !__GC_H */
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@ -363,9 +363,9 @@ void registerSubstitute(const Transaction & txn,
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}
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Substitutes querySubstitutes(const Path & srcPath)
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Substitutes querySubstitutes(const Transaction & txn, const Path & srcPath)
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{
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return readSubstitutes(noTxn, srcPath);
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return readSubstitutes(txn, srcPath);
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}
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@ -411,6 +411,13 @@ static void invalidatePath(const Path & path, Transaction & txn)
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debug(format("unregistering path `%1%'") % path);
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nixDB.delPair(txn, dbValidPaths, path);
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/* Clear the `references' entry for this path, as well as the
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inverse `referers' entries; but only if there are no
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substitutes for this path. This maintains the cleanup
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invariant. */
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if (querySubstitutes(txn, path).size() == 0)
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setReferences(txn, path, PathSet());
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}
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@ -45,7 +45,7 @@ void registerSubstitute(const Transaction & txn,
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const Path & srcPath, const Substitute & sub);
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/* Return the substitutes for the given path. */
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Substitutes querySubstitutes(const Path & srcPath);
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Substitutes querySubstitutes(const Transaction & txn, const Path & srcPath);
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/* Deregister all substitutes. */
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void clearSubstitutes();
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@ -573,7 +573,7 @@ static void opQuery(Globals & globals,
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Strings columns;
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if (printStatus) {
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Substitutes subs = querySubstitutes(i->drvPath);
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Substitutes subs = querySubstitutes(noTxn, i->drvPath);
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columns.push_back(
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(string) (installedPaths.find(i->outPath)
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!= installedPaths.end() ? "I" : "-")
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@ -62,11 +62,11 @@ Generations findGenerations(Path profile, int & curGen)
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static void makeNames(const Path & profile, unsigned int num,
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Path & generation, Path & gcrootDrv)
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Path & outLink, Path & drvLink)
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{
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Path prefix = (format("%1%-%2%") % profile % num).str();
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generation = prefix + "-link";
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gcrootDrv = prefix + "-drv.gcroot";
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outLink = prefix + "-output";
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drvLink = prefix + "-drv";
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}
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@ -79,20 +79,21 @@ Path createGeneration(Path profile, Path outPath, Path drvPath)
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unsigned int num = gens.size() > 0 ? gens.front().number : 0;
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/* Create the new generation. */
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Path generation, gcrootDrv;
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Path outLink, drvLink;
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while (1) {
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makeNames(profile, num, generation, gcrootDrv);
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if (symlink(outPath.c_str(), generation.c_str()) == 0) break;
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makeNames(profile, num, outLink, drvLink);
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if (symlink(outPath.c_str(), outLink.c_str()) == 0) break;
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if (errno != EEXIST)
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throw SysError(format("creating symlink `%1%'") % generation);
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throw SysError(format("creating symlink `%1%'") % outLink);
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/* Somebody beat us to it, retry with a higher number. */
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num++;
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}
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writeStringToFile(gcrootDrv, drvPath);
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if (symlink(drvPath.c_str(), drvLink.c_str()) != 0)
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throw SysError(format("creating symlink `%1%'") % drvLink);
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return generation;
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return outLink;
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}
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@ -274,61 +274,32 @@ static void opIsValid(Strings opFlags, Strings opArgs)
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static void opGC(Strings opFlags, Strings opArgs)
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{
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#if 0
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GCAction action;
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/* Do what? */
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enum { soPrintLive, soPrintDead, soDelete } subOp;
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time_t minAge = 0;
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for (Strings::iterator i = opFlags.begin();
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i != opFlags.end(); ++i)
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if (*i == "--print-live") subOp = soPrintLive;
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else if (*i == "--print-dead") subOp = soPrintDead;
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else if (*i == "--delete") subOp = soDelete;
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else if (*i == "--min-age") {
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int n;
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if (opArgs.size() == 0 || !string2Int(opArgs.front(), n))
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throw UsageError("`--min-age' requires an integer argument");
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minAge = n;
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}
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if (*i == "--print-live") action = gcReturnLive;
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else if (*i == "--print-dead") action = gcReturnDead;
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else if (*i == "--delete") action = gcDeleteDead;
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else throw UsageError(format("bad sub-operation `%1%' in GC") % *i);
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Paths roots;
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/* Read the roots. */
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PathSet roots;
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while (1) {
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Path root;
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getline(cin, root);
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if (cin.eof()) break;
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roots.push_back(root);
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roots.insert(root);
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}
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PathSet live = findLivePaths(roots);
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PathSet result;
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collectGarbage(roots, action, result);
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if (subOp == soPrintLive) {
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for (PathSet::iterator i = live.begin(); i != live.end(); ++i)
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if (action != gcDeleteDead) {
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for (PathSet::iterator i = result.begin(); i != result.end(); ++i)
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cout << *i << endl;
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return;
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}
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PathSet dead = findDeadPaths(live, minAge * 3600);
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if (subOp == soPrintDead) {
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for (PathSet::iterator i = dead.begin(); i != dead.end(); ++i)
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cout << *i << endl;
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return;
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}
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if (subOp == soDelete) {
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/* !!! What happens if the garbage collector run is aborted
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halfway through? In particular, dead paths can always
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become live again (through re-instantiation), and might
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then refer to deleted paths. => check instantiation
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invariants */
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for (PathSet::iterator i = dead.begin(); i != dead.end(); ++i) {
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printMsg(lvlInfo, format("deleting `%1%'") % *i);
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deleteFromStore(*i);
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}
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}
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#endif
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}
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