lix/src/libstore/gc.cc

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#include "globals.hh"
#include "misc.hh"
#include "pathlocks.hh"
#include "local-store.hh"
#include <boost/shared_ptr.hpp>
#include <functional>
#include <queue>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
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#ifdef __CYGWIN__
#include <windows.h>
#include <sys/cygwin.h>
#endif
namespace nix {
static string gcLockName = "gc.lock";
static string tempRootsDir = "temproots";
static string gcRootsDir = "gcroots";
static const int defaultGcLevel = 1000;
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/* Acquire the global GC lock. This is used to prevent new Nix
processes from starting after the temporary root files have been
read. To be precise: when they try to create a new temporary root
file, they will block until the garbage collector has finished /
yielded the GC lock. */
static int openGCLock(LockType lockType)
{
Path fnGCLock = (format("%1%/%2%")
% nixStateDir % gcLockName).str();
debug(format("acquiring global GC lock `%1%'") % fnGCLock);
AutoCloseFD fdGCLock = open(fnGCLock.c_str(), O_RDWR | O_CREAT, 0600);
if (fdGCLock == -1)
throw SysError(format("opening global GC lock `%1%'") % fnGCLock);
if (!lockFile(fdGCLock, lockType, false)) {
printMsg(lvlError, format("waiting for the big garbage collector lock..."));
lockFile(fdGCLock, lockType, true);
}
/* !!! Restrict read permission on the GC root. Otherwise any
process that can open the file for reading can DoS the
collector. */
return fdGCLock.borrow();
}
void createSymlink(const Path & link, const Path & target, bool careful)
{
/* Create directories up to `gcRoot'. */
createDirs(dirOf(link));
/* !!! shouldn't removing and creating the symlink be atomic? */
/* Remove the old symlink. */
if (pathExists(link)) {
if (careful && (!isLink(link) || !isInStore(readLink(link))))
throw Error(format("cannot create symlink `%1%'; already exists") % link);
unlink(link.c_str());
}
/* And create the new one. */
if (symlink(target.c_str(), link.c_str()) == -1)
throw SysError(format("symlinking `%1%' to `%2%'")
% link % target);
}
void LocalStore::syncWithGC()
{
AutoCloseFD fdGCLock = openGCLock(ltRead);
}
void LocalStore::addIndirectRoot(const Path & path)
{
string hash = printHash32(hashString(htSHA1, path));
Path realRoot = canonPath((format("%1%/%2%/auto/%3%")
% nixStateDir % gcRootsDir % hash).str());
createSymlink(realRoot, path, false);
}
Path addPermRoot(const Path & _storePath, const Path & _gcRoot,
bool indirect, bool allowOutsideRootsDir)
{
Path storePath(canonPath(_storePath));
Path gcRoot(canonPath(_gcRoot));
assertStorePath(storePath);
if (isInStore(gcRoot))
throw Error(format(
"creating a garbage collector root (%1%) in the Nix store is forbidden "
"(are you running nix-build inside the store?)") % gcRoot);
if (indirect) {
createSymlink(gcRoot, storePath, true);
store->addIndirectRoot(gcRoot);
}
else {
if (!allowOutsideRootsDir) {
Path rootsDir = canonPath((format("%1%/%2%") % nixStateDir % gcRootsDir).str());
if (string(gcRoot, 0, rootsDir.size() + 1) != rootsDir + "/")
throw Error(format(
"path `%1%' is not a valid garbage collector root; "
"it's not in the directory `%2%'")
% gcRoot % rootsDir);
}
createSymlink(gcRoot, storePath, false);
}
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/* Check that the root can be found by the garbage collector.
!!! This can be very slow on machines that have many roots.
Instead of reading all the roots, it would be more efficient to
check if the root is in a directory in or linked from the
gcroots directory. */
if (queryBoolSetting("gc-check-reachability", true)) {
Roots roots = store->findRoots();
if (roots.find(gcRoot) == roots.end())
printMsg(lvlError,
format(
"warning: `%1%' is not in a directory where the garbage collector looks for roots; "
"therefore, `%2%' might be removed by the garbage collector")
% gcRoot % storePath);
}
/* Grab the global GC root, causing us to block while a GC is in
progress. This prevents the set of permanent roots from
increasing while a GC is in progress. */
store->syncWithGC();
return gcRoot;
}
/* The file to which we write our temporary roots. */
static Path fnTempRoots;
static AutoCloseFD fdTempRoots;
void LocalStore::addTempRoot(const Path & path)
{
/* Create the temporary roots file for this process. */
if (fdTempRoots == -1) {
while (1) {
Path dir = (format("%1%/%2%") % nixStateDir % tempRootsDir).str();
createDirs(dir);
fnTempRoots = (format("%1%/%2%")
% dir % getpid()).str();
AutoCloseFD fdGCLock = openGCLock(ltRead);
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if (pathExists(fnTempRoots))
/* It *must* be stale, since there can be no two
processes with the same pid. */
deletePath(fnTempRoots);
fdTempRoots = openLockFile(fnTempRoots, true);
fdGCLock.close();
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/* Note that on Cygwin a lot of the following complexity
is unnecessary, since we cannot delete open lock
files. If we have the lock file open, then it's valid;
if we can delete it, then it wasn't in use any more.
Also note that on Cygwin we cannot "upgrade" a lock
from a read lock to a write lock. */
#ifndef __CYGWIN__
debug(format("acquiring read lock on `%1%'") % fnTempRoots);
lockFile(fdTempRoots, ltRead, true);
/* Check whether the garbage collector didn't get in our
way. */
struct stat st;
if (fstat(fdTempRoots, &st) == -1)
throw SysError(format("statting `%1%'") % fnTempRoots);
if (st.st_size == 0) break;
/* The garbage collector deleted this file before we could
get a lock. (It won't delete the file after we get a
lock.) Try again. */
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#else
break;
#endif
}
}
/* Upgrade the lock to a write lock. This will cause us to block
if the garbage collector is holding our lock. */
debug(format("acquiring write lock on `%1%'") % fnTempRoots);
lockFile(fdTempRoots, ltWrite, true);
string s = path + '\0';
writeFull(fdTempRoots, (const unsigned char *) s.c_str(), s.size());
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#ifndef __CYGWIN__
/* Downgrade to a read lock. */
debug(format("downgrading to read lock on `%1%'") % fnTempRoots);
lockFile(fdTempRoots, ltRead, true);
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#else
debug(format("releasing write lock on `%1%'") % fnTempRoots);
lockFile(fdTempRoots, ltNone, true);
#endif
}
void removeTempRoots()
{
if (fdTempRoots != -1) {
fdTempRoots.close();
unlink(fnTempRoots.c_str());
}
}
typedef boost::shared_ptr<AutoCloseFD> FDPtr;
typedef list<FDPtr> FDs;
static void readTempRoots(PathSet & tempRoots, FDs & fds)
{
/* Read the `temproots' directory for per-process temporary root
files. */
Strings tempRootFiles = readDirectory(
(format("%1%/%2%") % nixStateDir % tempRootsDir).str());
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foreach (Strings::iterator, i, tempRootFiles) {
Path path = (format("%1%/%2%/%3%") % nixStateDir % tempRootsDir % *i).str();
debug(format("reading temporary root file `%1%'") % path);
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#ifdef __CYGWIN__
/* On Cygwin we just try to delete the lock file. */
char win32Path[MAX_PATH];
cygwin_conv_to_full_win32_path(path.c_str(), win32Path);
if (DeleteFile(win32Path)) {
printMsg(lvlError, format("removed stale temporary roots file `%1%'")
% path);
continue;
} else
debug(format("delete of `%1%' failed: %2%") % path % GetLastError());
#endif
FDPtr fd(new AutoCloseFD(open(path.c_str(), O_RDWR, 0666)));
if (*fd == -1) {
/* It's okay if the file has disappeared. */
if (errno == ENOENT) continue;
throw SysError(format("opening temporary roots file `%1%'") % path);
}
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/* This should work, but doesn't, for some reason. */
//FDPtr fd(new AutoCloseFD(openLockFile(path, false)));
//if (*fd == -1) continue;
#ifndef __CYGWIN__
/* Try to acquire a write lock without blocking. This can
only succeed if the owning process has died. In that case
we don't care about its temporary roots. */
if (lockFile(*fd, ltWrite, false)) {
printMsg(lvlError, format("removing stale temporary roots file `%1%'")
% path);
unlink(path.c_str());
writeFull(*fd, (const unsigned char *) "d", 1);
continue;
}
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#endif
/* Acquire a read lock. This will prevent the owning process
from upgrading to a write lock, therefore it will block in
addTempRoot(). */
debug(format("waiting for read lock on `%1%'") % path);
lockFile(*fd, ltRead, true);
/* Read the entire file. */
string contents = readFile(*fd);
/* Extract the roots. */
string::size_type pos = 0, end;
while ((end = contents.find((char) 0, pos)) != string::npos) {
Path root(contents, pos, end - pos);
debug(format("got temporary root `%1%'") % root);
assertStorePath(root);
tempRoots.insert(root);
pos = end + 1;
}
fds.push_back(fd); /* keep open */
}
}
static void findRoots(const Path & path, bool recurseSymlinks,
bool deleteStale, Roots & roots)
{
try {
struct stat st;
if (lstat(path.c_str(), &st) == -1)
throw SysError(format("statting `%1%'") % path);
printMsg(lvlVomit, format("looking at `%1%'") % path);
if (S_ISDIR(st.st_mode)) {
Strings names = readDirectory(path);
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foreach (Strings::iterator, i, names)
findRoots(path + "/" + *i, recurseSymlinks, deleteStale, roots);
}
else if (S_ISLNK(st.st_mode)) {
Path target = absPath(readLink(path), dirOf(path));
if (isInStore(target)) {
debug(format("found root `%1%' in `%2%'")
% target % path);
Path storePath = toStorePath(target);
if (store->isValidPath(storePath))
roots[path] = storePath;
else
printMsg(lvlInfo, format("skipping invalid root from `%1%' to `%2%'")
% path % storePath);
}
else if (recurseSymlinks) {
if (pathExists(target))
findRoots(target, false, deleteStale, roots);
else if (deleteStale) {
printMsg(lvlInfo, format("removing stale link from `%1%' to `%2%'") % path % target);
/* Note that we only delete when recursing, i.e.,
when we are still in the `gcroots' tree. We
never delete stuff outside that tree. */
unlink(path.c_str());
}
}
}
}
catch (SysError & e) {
/* We only ignore permanent failures. */
if (e.errNo == EACCES || e.errNo == ENOENT || e.errNo == ENOTDIR)
printMsg(lvlInfo, format("cannot read potential root `%1%'") % path);
else
throw;
}
}
static Roots findRoots(bool deleteStale)
{
Roots roots;
Path rootsDir = canonPath((format("%1%/%2%") % nixStateDir % gcRootsDir).str());
findRoots(rootsDir, true, deleteStale, roots);
return roots;
}
Roots LocalStore::findRoots()
{
return nix::findRoots(false);
}
static void addAdditionalRoots(PathSet & roots)
{
Path rootFinder = getEnv("NIX_ROOT_FINDER",
nixLibexecDir + "/nix/find-runtime-roots.pl");
if (rootFinder.empty()) return;
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debug(format("executing `%1%' to find additional roots") % rootFinder);
string result = runProgram(rootFinder);
Strings paths = tokenizeString(result, "\n");
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foreach (Strings::iterator, i, paths) {
if (isInStore(*i)) {
Path path = toStorePath(*i);
if (roots.find(path) == roots.end() && store->isValidPath(path)) {
debug(format("found additional root `%1%'") % path);
roots.insert(path);
}
}
}
}
static void dfsVisit(const PathSet & paths, const Path & path,
PathSet & visited, Paths & sorted)
{
if (visited.find(path) != visited.end()) return;
visited.insert(path);
PathSet references;
if (store->isValidPath(path))
store->queryReferences(path, references);
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foreach (PathSet::iterator, i, references)
/* Don't traverse into paths that don't exist. That can
happen due to substitutes for non-existent paths. */
if (*i != path && paths.find(*i) != paths.end())
dfsVisit(paths, *i, visited, sorted);
sorted.push_front(path);
}
Paths topoSortPaths(const PathSet & paths)
{
Paths sorted;
PathSet visited;
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foreach (PathSet::const_iterator, i, paths)
dfsVisit(paths, *i, visited, sorted);
return sorted;
}
static time_t lastFileAccessTime(const Path & path)
{
checkInterrupt();
struct stat st;
if (lstat(path.c_str(), &st) == -1)
throw SysError(format("statting `%1%'") % path);
if (S_ISDIR(st.st_mode)) {
time_t last = 0;
Strings names = readDirectory(path);
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foreach (Strings::iterator, i, names) {
time_t t = lastFileAccessTime(path + "/" + *i);
if (t > last) last = t;
}
return last;
}
else if (S_ISLNK(st.st_mode)) return 0;
else return st.st_atime;
}
struct GCLimitReached { };
void LocalStore::gcPath(const GCOptions & options, GCResults & results,
const Path & path)
{
results.paths.insert(path);
if (!pathExists(path)) return;
/* Okay, it's safe to delete. */
unsigned long long bytesFreed, blocksFreed;
deleteFromStore(path, bytesFreed, blocksFreed);
results.bytesFreed += bytesFreed;
results.blocksFreed += blocksFreed;
if (options.maxFreed && results.bytesFreed > options.maxFreed) {
printMsg(lvlInfo, format("deleted more than %1% bytes; stopping") % options.maxFreed);
throw GCLimitReached();
}
if (options.maxLinks) {
struct stat st;
if (stat(nixStore.c_str(), &st) == -1)
throw SysError(format("statting `%1%'") % nixStore);
if (st.st_nlink < options.maxLinks) {
printMsg(lvlInfo, format("link count on the store has dropped below %1%; stopping") % options.maxLinks);
throw GCLimitReached();
}
}
}
void LocalStore::gcPathRecursive(const GCOptions & options,
GCResults & results, PathSet & done, const Path & path)
{
if (done.find(path) != done.end()) return;
done.insert(path);
startNest(nest, lvlDebug, format("looking at `%1%'") % path);
/* Delete all the referrers first. They must be garbage too,
since if they were live, then the current path would also be
live. Note that deleteFromStore() below still makes sure that
the referrer set has become empty, just in case. (However that
doesn't guard against deleting top-level paths that are only
reachable from GC roots.) */
PathSet referrers;
if (isValidPath(path))
queryReferrers(path, referrers);
foreach (PathSet::iterator, i, referrers)
if (*i != path) gcPathRecursive(options, results, done, *i);
printMsg(lvlInfo, format("deleting `%1%'") % path);
gcPath(options, results, path);
}
struct CachingAtimeComparator : public std::binary_function<Path, Path, bool>
{
std::map<Path, time_t> cache;
time_t lookup(const Path & p)
{
std::map<Path, time_t>::iterator i = cache.find(p);
if (i != cache.end()) return i->second;
debug(format("computing atime of `%1%'") % p);
cache[p] = lastFileAccessTime(p);
assert(cache.find(p) != cache.end());
return cache[p];
}
bool operator () (const Path & p1, const Path & p2)
{
return lookup(p2) < lookup(p1);
}
};
static string showTime(const string & format, time_t t)
{
char s[128];
strftime(s, sizeof s, format.c_str(), localtime(&t));
return string(s);
}
static bool isLive(const Path & path, const PathSet & livePaths,
const PathSet & tempRoots, const PathSet & tempRootsClosed)
{
if (livePaths.find(path) != livePaths.end() ||
tempRootsClosed.find(path) != tempRootsClosed.end()) return true;
/* A lock file belonging to a path that we're building right
now isn't garbage. */
if (hasSuffix(path, ".lock") && tempRoots.find(string(path, 0, path.size() - 5)) != tempRoots.end())
return true;
/* Don't delete .chroot directories for derivations that are
currently being built. */
if (hasSuffix(path, ".chroot") && tempRoots.find(string(path, 0, path.size() - 7)) != tempRoots.end())
return true;
return false;
}
void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
{
bool gcKeepOutputs =
queryBoolSetting("gc-keep-outputs", false);
bool gcKeepDerivations =
queryBoolSetting("gc-keep-derivations", true);
int gcKeepOutputsThreshold =
queryIntSetting ("gc-keep-outputs-threshold", defaultGcLevel);
/* Acquire the global GC root. This prevents
a) New roots from being added.
b) Processes from creating new temporary root files. */
AutoCloseFD fdGCLock = openGCLock(ltWrite);
/* Find the roots. Since we've grabbed the GC lock, the set of
permanent roots cannot increase now. */
printMsg(lvlError, format("finding garbage collector roots..."));
Roots rootMap = options.ignoreLiveness ? Roots() : nix::findRoots(true);
PathSet roots;
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foreach (Roots::iterator, i, rootMap) roots.insert(i->second);
/* Add additional roots returned by the program specified by the
NIX_ROOT_FINDER environment variable. This is typically used
to add running programs to the set of roots (to prevent them
from being garbage collected). */
if (!options.ignoreLiveness)
addAdditionalRoots(roots);
if (options.action == GCOptions::gcReturnRoots) {
results.paths = roots;
return;
}
/* Determine the live paths which is just the closure of the
roots under the `references' relation. */
printMsg(lvlError, format("computing live paths..."));
PathSet livePaths;
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foreach (PathSet::const_iterator, i, roots)
computeFSClosure(canonPath(*i), livePaths);
if (gcKeepDerivations) {
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foreach (PathSet::iterator, i, livePaths) {
/* Note that the deriver need not be valid (e.g., if we
previously ran the collector with `gcKeepDerivations'
turned off). */
Path deriver = queryDeriver(*i);
if (deriver != "" && isValidPath(deriver))
computeFSClosure(deriver, livePaths);
}
}
if (gcKeepOutputs) {
/* Hmz, identical to storePathRequisites in nix-store. */
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foreach (PathSet::iterator, i, livePaths)
if (isDerivation(*i)) {
Derivation drv = derivationFromPath(*i);
string gcLevelStr = drv.env["__gcLevel"];
int gcLevel;
if (!string2Int(gcLevelStr, gcLevel))
gcLevel = defaultGcLevel;
if (gcLevel >= gcKeepOutputsThreshold)
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foreach (DerivationOutputs::iterator, j, drv.outputs)
if (isValidPath(j->second.path))
computeFSClosure(j->second.path, livePaths);
}
}
if (options.action == GCOptions::gcReturnLive) {
results.paths = livePaths;
return;
}
/* Read the temporary roots. This acquires read locks on all
per-process temporary root files. So after this point no paths
can be added to the set of temporary roots. */
PathSet tempRoots;
FDs fds;
readTempRoots(tempRoots, fds);
/* Close the temporary roots. Note that we *cannot* do this in
readTempRoots(), because there we may not have all locks yet,
meaning that an invalid path can become valid (and thus add to
the references graph) after we have added it to the closure
(and computeFSClosure() assumes that the presence of a path
means that it has already been closed). */
PathSet tempRootsClosed;
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foreach (PathSet::iterator, i, tempRoots)
if (isValidPath(*i))
computeFSClosure(*i, tempRootsClosed);
else
tempRootsClosed.insert(*i);
/* After this point the set of roots or temporary roots cannot
increase, since we hold locks on everything. So everything
that is not currently in in `livePaths' or `tempRootsClosed'
can be deleted. */
/* Read the Nix store directory to find all currently existing
paths and filter out all live paths. */
printMsg(lvlError, format("reading the Nix store..."));
PathSet storePaths;
if (options.action != GCOptions::gcDeleteSpecific) {
Paths entries = readDirectory(nixStore);
foreach (Paths::iterator, i, entries) {
Path path = canonPath(nixStore + "/" + *i);
if (!isLive(path, livePaths, tempRoots, tempRootsClosed)) storePaths.insert(path);
}
}
else {
foreach (PathSet::iterator, i, options.pathsToDelete) {
assertStorePath(*i);
storePaths.insert(*i);
if (isLive(*i, livePaths, tempRoots, tempRootsClosed))
throw Error(format("cannot delete path `%1%' since it is still alive") % *i);
}
}
if (options.action == GCOptions::gcReturnDead) {
results.paths.insert(storePaths.begin(), storePaths.end());
return;
}
/* Delete all dead store paths (or until one of the stop
conditions is reached). */
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PathSet done;
try {
if (!options.useAtime) {
/* Delete the paths, respecting the partial ordering
determined by the references graph. */
printMsg(lvlError, format("deleting garbage..."));
foreach (PathSet::iterator, i, storePaths)
gcPathRecursive(options, results, done, *i);
}
else {
/* Delete in order of ascending last access time, still
maintaining the partial ordering of the reference
graph. Note that we can't use a topological sort for
this because that takes time O(V+E), and in this case
E=O(V^2) (i.e. the graph is dense because of the edges
due to the atime ordering). So instead we put all
deletable paths in a priority queue (ordered by atime),
and after deleting a path, add additional paths that
have become deletable to the priority queue. */
CachingAtimeComparator atimeComp;
/* Create a priority queue that orders paths by ascending
atime. This is why C++ needs type inferencing... */
std::priority_queue<Path, vector<Path>, binary_function_ref_adapter<CachingAtimeComparator> > prioQueue =
std::priority_queue<Path, vector<Path>, binary_function_ref_adapter<CachingAtimeComparator> >(binary_function_ref_adapter<CachingAtimeComparator>(&atimeComp));
/* Initially put the paths that are invalid or have no
referrers into the priority queue. */
printMsg(lvlError, format("finding deletable paths..."));
foreach (PathSet::iterator, i, storePaths) {
checkInterrupt();
/* We can safely delete a path if it's invalid or
it has no referrers. Note that all the invalid
paths will be deleted in the first round. */
if (isValidPath(*i)) {
if (queryReferrersNoSelf(*i).empty()) prioQueue.push(*i);
} else prioQueue.push(*i);
}
debug(format("%1% initially deletable paths") % prioQueue.size());
/* Now delete everything in the order of the priority
queue until nothing is left. */
printMsg(lvlError, format("deleting garbage..."));
while (!prioQueue.empty()) {
checkInterrupt();
Path path = prioQueue.top(); prioQueue.pop();
if (options.maxAtime != (time_t) -1 &&
atimeComp.lookup(path) > options.maxAtime)
continue;
printMsg(lvlInfo, format("deleting `%1%' (last accessed %2%)") % path % showTime("%F %H:%M:%S", atimeComp.lookup(path)));
PathSet references;
if (isValidPath(path)) references = queryReferencesNoSelf(path);
gcPath(options, results, path);
/* For each reference of the current path, see if the
reference has now become deletable (i.e. is in the
set of dead paths and has no referrers left). If
so add it to the priority queue. */
foreach (PathSet::iterator, i, references) {
if (storePaths.find(*i) != storePaths.end() &&
queryReferrersNoSelf(*i).empty())
{
debug(format("path `%1%' has become deletable") % *i);
prioQueue.push(*i);
}
}
}
}
} catch (GCLimitReached & e) {
}
}
}