286 lines
9.4 KiB
C++
286 lines
9.4 KiB
C++
#include "globals.hh"
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#include "gc.hh"
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#include "build.hh"
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#include "pathlocks.hh"
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#include <boost/shared_ptr.hpp>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <unistd.h>
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static string tempRootsDir = "temproots";
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/* The file to which we write our temporary roots. */
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Path fnTempRoots;
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static AutoCloseFD fdTempRoots;
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void addTempRoot(const Path & path)
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{
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/* Create the temporary roots file for this process. */
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if (fdTempRoots == -1) {
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while (1) {
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fnTempRoots = (format("%1%/%2%/%3%")
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% nixStateDir % tempRootsDir % getpid()).str();
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fdTempRoots = open(fnTempRoots.c_str(), O_RDWR | O_CREAT | O_TRUNC, 0600);
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if (fdTempRoots == -1)
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throw SysError(format("opening temporary roots file `%1%'") % fnTempRoots);
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debug(format("acquiring read lock on `%1%'") % fnTempRoots);
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lockFile(fdTempRoots, ltRead, true);
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/* Check whether the garbage collector didn't get in our
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way. */
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struct stat st;
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if (fstat(fdTempRoots, &st) == -1)
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throw SysError(format("statting `%1%'") % fnTempRoots);
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if (st.st_size == 0) break;
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/* The garbage collector deleted this file before we could
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get a lock. (It won't delete the file after we get a
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lock.) Try again. */
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}
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}
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/* Upgrade the lock to a write lock. This will cause us to block
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if the garbage collector is holding our lock. */
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debug(format("acquiring write lock on `%1%'") % fnTempRoots);
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lockFile(fdTempRoots, ltWrite, true);
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string s = path + '\0';
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writeFull(fdTempRoots, (const unsigned char *) s.c_str(), s.size());
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/* Downgrade to a read lock. */
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debug(format("downgrading to read lock on `%1%'") % fnTempRoots);
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lockFile(fdTempRoots, ltRead, true);
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}
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void removeTempRoots()
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{
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if (fdTempRoots != -1) {
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fdTempRoots.close();
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unlink(fnTempRoots.c_str());
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}
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}
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typedef shared_ptr<AutoCloseFD> FDPtr;
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typedef list<FDPtr> FDs;
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static void readTempRoots(PathSet & tempRoots, FDs & fds)
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{
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/* Read the `temproots' directory for per-process temporary root
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files. */
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Strings tempRootFiles = readDirectory(
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(format("%1%/%2%") % nixStateDir % tempRootsDir).str());
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for (Strings::iterator i = tempRootFiles.begin();
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i != tempRootFiles.end(); ++i)
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{
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Path path = (format("%1%/%2%/%3%") % nixStateDir % tempRootsDir % *i).str();
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debug(format("reading temporary root file `%1%'") % path);
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FDPtr fd(new AutoCloseFD(open(path.c_str(), O_RDWR, 0666)));
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if (*fd == -1) {
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/* It's okay if the file has disappeared. */
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if (errno == ENOENT) continue;
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throw SysError(format("opening temporary roots file `%1%'") % path);
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}
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/* Try to acquire a write lock without blocking. This can
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only succeed if the owning process has died. In that case
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we don't care about its temporary roots. */
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if (lockFile(*fd, ltWrite, false)) {
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printMsg(lvlError, format("removing stale temporary roots file `%1%'")
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% path);
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unlink(path.c_str());
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writeFull(*fd, (const unsigned char *) "d", 1);
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continue;
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}
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/* Acquire a read lock. This will prevent the owning process
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from upgrading to a write lock, therefore it will block in
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addTempRoot(). */
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debug(format("waiting for read lock on `%1%'") % path);
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lockFile(*fd, ltRead, true);
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/* Read the entire file. */
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struct stat st;
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if (fstat(*fd, &st) == -1)
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throw SysError(format("statting `%1%'") % path);
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unsigned char buf[st.st_size]; /* !!! stack space */
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readFull(*fd, buf, st.st_size);
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/* Extract the roots. */
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string contents((char *) buf, st.st_size);
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unsigned int pos = 0, end;
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while ((end = contents.find((char) 0, pos)) != string::npos) {
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Path root(contents, pos, end - pos);
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debug(format("got temporary root `%1%'") % root);
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assertStorePath(root);
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tempRoots.insert(root);
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pos = end + 1;
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}
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fds.push_back(fd); /* keep open */
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}
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}
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static void dfsVisit(const PathSet & paths, const Path & path,
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PathSet & visited, Paths & sorted)
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{
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if (visited.find(path) != visited.end()) return;
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visited.insert(path);
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PathSet references;
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if (isValidPath(path))
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queryReferences(path, references);
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for (PathSet::iterator i = references.begin();
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i != references.end(); ++i)
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/* Don't traverse into paths that don't exist. That can
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happen due to substitutes for non-existent paths. */
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if (*i != path && paths.find(*i) != paths.end())
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dfsVisit(paths, *i, visited, sorted);
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sorted.push_front(path);
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}
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static Paths topoSort(const PathSet & paths)
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{
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Paths sorted;
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PathSet visited;
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for (PathSet::const_iterator i = paths.begin(); i != paths.end(); ++i)
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dfsVisit(paths, *i, visited, sorted);
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return sorted;
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}
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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 the global GC root. This prevents
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a) New roots from being added.
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b) Processes from creating new temporary root files. */
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/* !!! Restrict read permission on the GC root. Otherwise any
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process that can open the file for reading can DoS the
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collector. */
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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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/* Read the temporary roots. This acquires read locks on all
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per-process temporary root files. So after this point no paths
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can be added to the set of temporary roots. */
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PathSet tempRoots;
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FDs fds;
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readTempRoots(tempRoots, fds);
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/* Close the temporary roots. Note that we *cannot* do this in
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readTempRoots(), because there we may not have all locks yet,
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meaning that an invalid path can become valid (and thus add to
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the references graph) after we have added it to the closure
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(and computeFSClosure() assumes that the presence of a path
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means that it has already been closed). */
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PathSet tempRootsClosed;
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for (PathSet::iterator i = tempRoots.begin(); i != tempRoots.end(); ++i)
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if (isValidPath(*i))
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computeFSClosure(*i, tempRootsClosed);
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else
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tempRootsClosed.insert(*i);
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/* After this point the set of roots or temporary roots cannot
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increase, since we hold locks on everything. So everything
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that is not currently in in `livePaths' or `tempRootsClosed'
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can be deleted. */
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/* Read the Nix store directory to find all currently existing
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paths. */
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Paths storePaths = readDirectory(nixStore);
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PathSet storePaths2;
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for (Paths::iterator i = storePaths.begin(); i != storePaths.end(); ++i)
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storePaths2.insert(canonPath(nixStore + "/" + *i));
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/* Topologically sort them under the `referers' relation. That
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is, a < b iff a is in referers(b). This gives us the order in
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which things can be deleted safely. */
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/* !!! when we have multiple output paths per derivation, this
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will not work anymore because we get cycles. */
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storePaths = topoSort(storePaths2);
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for (Paths::iterator i = storePaths.begin(); i != storePaths.end(); ++i) {
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debug(format("considering deletion of `%1%'") % *i);
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if (livePaths.find(*i) != livePaths.end()) {
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debug(format("live path `%1%'") % *i);
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continue;
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}
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if (tempRootsClosed.find(*i) != tempRootsClosed.end()) {
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debug(format("temporary root `%1%'") % *i);
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continue;
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}
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debug(format("dead path `%1%'") % *i);
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result.insert(*i);
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AutoCloseFD fdLock;
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if (action == gcDeleteDead) {
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/* Only delete a lock file if we can acquire a write lock
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on it. That means that it's either stale, or the
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process that created it hasn't locked it yet. In the
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latter case the other process will detect that we
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deleted the lock, and retry (see pathlocks.cc). */
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if (i->size() >= 5 && string(*i, i->size() - 5) == ".lock") {
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fdLock = open(i->c_str(), O_RDWR);
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if (fdLock == -1) {
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if (errno == ENOENT) continue;
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throw SysError(format("opening lock file `%1%'") % *i);
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}
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if (!lockFile(fdLock, ltWrite, false)) {
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debug(format("skipping active lock `%1%'") % *i);
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continue;
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}
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}
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printMsg(lvlInfo, format("deleting `%1%'") % *i);
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/* Okay, it's safe to delete. */
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deleteFromStore(*i);
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if (fdLock != -1)
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/* Write token to stale (deleted) lock file. */
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writeFull(fdLock, (const unsigned char *) "d", 1);
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}
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}
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}
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