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Yet another rewrite of the garbage collector

Browse source 
But this time it's *obviously* correct!  No more segfaults due to
infinite recursions for sure, etc.

Also, move directories to /nix/store/trash instead of renaming them to
/nix/store/bla-gc-<pid>.  Then we can just delete /nix/store/trash at
the end.
This commit is contained in:
Eelco Dolstra 2012-12-20 17:32:15 +01:00
parent 9c29a2ed35
commit 06f62defe6
2 changed files with 145 additions and 138 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

273
src/libstore/gc.cc
View file

@ -396,24 +396,17 @@ struct LocalStore::GCState
GCResults & results;
PathSet roots;
PathSet tempRoots;
PathSet deleted;
PathSet live;
PathSet busy;
PathSet invalidated;
PathSet dead;
PathSet alive;
bool gcKeepOutputs;
bool gcKeepDerivations;
unsigned long long bytesInvalidated;
Path trashDir;
bool shouldDelete;
GCState(GCResults & results_) : results(results_), bytesInvalidated(0) { }
};
static bool shouldDelete(GCOptions::GCAction action)
{
return action == GCOptions::gcDeleteDead
|| action == GCOptions::gcDeleteSpecific;
}
bool LocalStore::isActiveTempFile(const GCState & state,
const Path & path, const string & suffix)
{
@ -424,154 +417,150 @@ bool LocalStore::isActiveTempFile(const GCState & state,
void LocalStore::deleteGarbage(GCState & state, const Path & path)
{
printMsg(lvlInfo, format("deleting `%1%'") % path);
unsigned long long bytesFreed;
deletePathWrapped(path, bytesFreed);
state.results.bytesFreed += bytesFreed;
}
bool LocalStore::tryToDelete(GCState & state, const Path & path)
void LocalStore::deletePathRecursive(GCState & state, const Path & path)
{
checkInterrupt();
if (path == linksDir) return true;
unsigned long long size = 0;
if (isValidPath(path)) {
PathSet referrers;
queryReferrers(path, referrers);
foreach (PathSet::iterator, i, referrers)
if (*i != path) deletePathRecursive(state, *i);
size = queryPathInfo(path).narSize;
invalidatePathChecked(path);
}
struct stat st;
if (lstat(path.c_str(), &st)) {
if (errno == ENOENT) return true;
if (errno == ENOENT) return;
throw SysError(format("getting status of %1%") % path);
}
if (state.deleted.find(path) != state.deleted.end()) return true;
if (state.live.find(path) != state.live.end()) return false;
printMsg(lvlInfo, format("deleting `%1%'") % path);
startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path);
/* If gc-keep-outputs and gc-keep-derivations are both set, we can
have cycles in the liveness graph, so we need to treat such
strongly connected components as a single unit (‘paths’). That
is, we can delete the elements of ‘paths’ only if all referrers
of ‘paths’ are garbage. */
PathSet paths, referrers;
Paths pathsSorted;
if (isValidPath(path)) {
/* Add derivers and outputs of ‘path’ to ‘paths’. */
PathSet todo;
todo.insert(path);
while (!todo.empty()) {
Path p = *todo.begin();
assertStorePath(p);
todo.erase(p);
if (paths.find(p) != paths.end()) continue;
paths.insert(p);
/* If gc-keep-derivations is set and this is a derivation,
then don't delete the derivation if any of the outputs
are live. */
if (state.gcKeepDerivations && isDerivation(p)) {
PathSet outputs = queryDerivationOutputs(p);
foreach (PathSet::iterator, i, outputs)
if (isValidPath(*i) && queryDeriver(*i) == p) todo.insert(*i);
}
/* If gc-keep-outputs is set, then don't delete this path
if there are derivers of this path that are not
garbage. */
if (state.gcKeepOutputs) {
PathSet derivers = queryValidDerivers(p);
foreach (PathSet::iterator, i, derivers) todo.insert(*i);
}
}
}
else {
/* A lock file belonging to a path that we're building right
now isn't garbage. */
if (isActiveTempFile(state, path, ".lock")) return false;
/* Don't delete .chroot directories for derivations that are
currently being built. */
if (isActiveTempFile(state, path, ".chroot")) return false;
paths.insert(path);
}
/* Check if any path in ‘paths’ is a root. */
foreach (PathSet::iterator, i, paths)
if (state.roots.find(*i) != state.roots.end()) {
printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % *i);
goto isLive;
}
/* Recursively try to delete the referrers of this strongly
connected component. If any referrer can't be deleted, then
these paths can't be deleted either. */
foreach (PathSet::iterator, i, paths)
if (isValidPath(*i)) queryReferrers(*i, referrers);
foreach (PathSet::iterator, i, referrers)
if (paths.find(*i) == paths.end() && !tryToDelete(state, *i)) {
printMsg(lvlDebug, format("cannot delete `%1%' because it has live referrers") % *i);
goto isLive;
}
/* The paths are garbage, so delete them. */
pathsSorted = topoSortPaths(*this, paths);
foreach (Paths::iterator, i, pathsSorted) {
if (shouldDelete(state.options.action)) {
/* If it's a valid path that's not a regular file or
symlink, invalidate it, rename it, and schedule it for
deletion. The renaming is to ensure that later (when
we're not holding the global GC lock) we can delete the
path without being afraid that the path has become
alive again. Otherwise delete it right away. */
if (isValidPath(*i)) {
/* If the path is not a regular file or symlink, move it to the
trash directory. The move is to ensure that later (when we're
not holding the global GC lock) we can delete the path without
being afraid that the path has become alive again. Otherwise
delete it right away. */
if (S_ISDIR(st.st_mode)) {
printMsg(lvlInfo, format("invalidating `%1%'") % *i);
// Estimate the amount freed using the narSize field.
state.bytesInvalidated += queryPathInfo(*i).narSize;
invalidatePathChecked(*i);
makeMutable(i->c_str());
// Estimate the amount freed using the narSize field. FIXME:
// if the path was not valid, need to determine the actual
// size.
state.bytesInvalidated += size;
makeMutable(path.c_str());
// Mac OS X cannot rename directories if they are read-only.
if (chmod(i->c_str(), st.st_mode | S_IWUSR) == -1)
throw SysError(format("making `%1%' writable") % *i);
Path tmp = (format("%1%-gc-%2%") % *i % getpid()).str();
if (rename(i->c_str(), tmp.c_str()))
throw SysError(format("unable to rename `%1%' to `%2%'") % *i % tmp);
state.invalidated.insert(tmp);
} else {
invalidatePathChecked(*i);
deleteGarbage(state, *i);
}
if (chmod(path.c_str(), st.st_mode | S_IWUSR) == -1)
throw SysError(format("making `%1%' writable") % path);
Path tmp = state.trashDir + "/" + baseNameOf(path);
if (rename(path.c_str(), tmp.c_str()))
throw SysError(format("unable to rename `%1%' to `%2%'") % path % tmp);
} else
deleteGarbage(state, *i);
deleteGarbage(state, path);
if (state.results.bytesFreed + state.bytesInvalidated > state.options.maxFreed) {
printMsg(lvlInfo, format("deleted or invalidated more than %1% bytes; stopping") % state.options.maxFreed);
throw GCLimitReached();
}
} else
printMsg(lvlTalkative, format("would delete `%1%'") % *i);
state.deleted.insert(*i);
if (state.options.action != GCOptions::gcReturnLive)
state.results.paths.insert(*i);
}
bool LocalStore::canReachRoot(GCState & state, PathSet & visited, const Path & path)
{
if (visited.find(path) != visited.end()) return false;
if (state.alive.find(path) != state.alive.end()) {
return true;
isLive:
foreach (PathSet::iterator, i, paths) {
state.live.insert(*i);
if (state.options.action == GCOptions::gcReturnLive)
state.results.paths.insert(*i);
}
if (state.dead.find(path) != state.dead.end()) {
return false;
}
if (state.roots.find(path) != state.roots.end()) {
printMsg(lvlDebug, format("cannot delete `%1%' because it's a root") % path);
state.alive.insert(path);
return true;
}
visited.insert(path);
if (!isValidPath(path)) return false;
PathSet incoming;
/* Don't delete this path if any of its referrers are alive. */
queryReferrers(path, incoming);
/* If gc-keep-derivations is set and this is a derivation, then
don't delete the derivation if any of the outputs are alive. */
if (state.gcKeepDerivations && isDerivation(path)) {
PathSet outputs = queryDerivationOutputs(path);
foreach (PathSet::iterator, i, outputs)
if (isValidPath(*i) && queryDeriver(*i) == path)
incoming.insert(*i);
}
/* If gc-keep-outputs is set, then don't delete this path if there
are derivers of this path that are not garbage. */
if (state.gcKeepOutputs) {
PathSet derivers = queryValidDerivers(path);
foreach (PathSet::iterator, i, derivers)
incoming.insert(*i);
}
foreach (PathSet::iterator, i, incoming)
if (*i != path)
if (canReachRoot(state, visited, *i)) {
state.alive.insert(path);
return true;
}
return false;
}
void LocalStore::tryToDelete(GCState & state, const Path & path)
{
checkInterrupt();
if (path == linksDir || path == state.trashDir) return;
startNest(nest, lvlDebug, format("considering whether to delete `%1%'") % path);
if (!isValidPath(path)) {
/* A lock file belonging to a path that we're building right
now isn't garbage. */
if (isActiveTempFile(state, path, ".lock")) return;
/* Don't delete .chroot directories for derivations that are
currently being built. */
if (isActiveTempFile(state, path, ".chroot")) return;
}
PathSet visited;
if (canReachRoot(state, visited, path)) {
printMsg(lvlDebug, format("cannot delete `%1%' because it's still reachable") % path);
} else {
/* No path we visited was a root, so everything is garbage.
But we only delete ‘path’ and its referrers here so that
‘nix-store --delete’ doesn't have the unexpected effect of
recursing into derivations and outputs. */
state.dead.insert(visited.begin(), visited.end());
if (state.shouldDelete)
deletePathRecursive(state, path);
}
}
/* Unlink all files in /nix/store/.links that have a link count of 1,
which indicates that there are no other links and so they can be
@ -625,7 +614,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
{
GCState state(results);
state.options = options;
state.trashDir = settings.nixStore + "/trash";
state.gcKeepOutputs = settings.gcKeepOutputs;
state.gcKeepDerivations = settings.gcKeepDerivations;
@ -638,6 +627,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
state.gcKeepDerivations = false;
}
state.shouldDelete = options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific;
/* Acquire the global GC root. This prevents
a) New roots from being added.
b) Processes from creating new temporary root files. */
@ -668,6 +659,8 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
increase, since we hold locks on everything. So everything
that is not reachable from `roots'. */
if (state.shouldDelete) createDirs(state.trashDir);
/* Now either delete all garbage paths, or just the specified
paths (for gcDeleteSpecific). */
@ -675,13 +668,14 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
foreach (PathSet::iterator, i, options.pathsToDelete) {
assertStorePath(*i);
if (!tryToDelete(state, *i))
tryToDelete(state, *i);
if (state.dead.find(*i) == state.dead.end())
throw Error(format("cannot delete path `%1%' since it is still alive") % *i);
}
} else if (options.maxFreed > 0) {
if (shouldDelete(state.options.action))
if (state.shouldDelete)
printMsg(lvlError, format("deleting garbage..."));
else
printMsg(lvlError, format("determining live/dead paths..."));
@ -727,13 +721,22 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
}
}
if (state.options.action == GCOptions::gcReturnLive) {
state.results.paths = state.alive;
return;
}
if (state.options.action == GCOptions::gcReturnDead) {
state.results.paths = state.dead;
return;
}
/* Allow other processes to add to the store from here on. */
fdGCLock.close();
/* Delete the invalidated paths now that the lock has been
released. */
foreach (PathSet::iterator, i, state.invalidated)
deleteGarbage(state, *i);
/* Delete the trash directory. */
printMsg(lvlInfo, format("deleting `%1%'") % state.trashDir);
deleteGarbage(state, state.trashDir);
/* Clean up the links directory. */
if (options.action == GCOptions::gcDeleteDead || options.action == GCOptions::gcDeleteSpecific) {

6
src/libstore/local-store.hh
View file

@ -276,7 +276,11 @@ private:
void deleteGarbage(GCState & state, const Path & path);
bool tryToDelete(GCState & state, const Path & path);
void tryToDelete(GCState & state, const Path & path);
bool canReachRoot(GCState & state, PathSet & visited, const Path & path);
void deletePathRecursive(GCState & state, const Path & path);
bool isActiveTempFile(const GCState & state,
const Path & path, const string & suffix);