diff options
Diffstat (limited to 'third_party/nix/src/libstore/pathlocks.cc')
| -rw-r--r-- | third_party/nix/src/libstore/pathlocks.cc | 262 |
1 files changed, 120 insertions, 142 deletions
diff --git a/third_party/nix/src/libstore/pathlocks.cc b/third_party/nix/src/libstore/pathlocks.cc index 2635e3940a..7fa32e21a6 100644 --- a/third_party/nix/src/libstore/pathlocks.cc +++ b/third_party/nix/src/libstore/pathlocks.cc @@ -1,178 +1,156 @@ #include "pathlocks.hh" -#include "util.hh" -#include "sync.hh" - -#include <cerrno> -#include <cstdlib> - #include <fcntl.h> -#include <sys/types.h> -#include <sys/stat.h> #include <sys/file.h> - +#include <sys/stat.h> +#include <sys/types.h> +#include <cerrno> +#include <cstdlib> +#include "sync.hh" +#include "util.hh" namespace nix { +AutoCloseFD openLockFile(const Path& path, bool create) { + AutoCloseFD fd; -AutoCloseFD openLockFile(const Path & path, bool create) -{ - AutoCloseFD fd; - - fd = open(path.c_str(), O_CLOEXEC | O_RDWR | (create ? O_CREAT : 0), 0600); - if (!fd && (create || errno != ENOENT)) - throw SysError(format("opening lock file '%1%'") % path); + fd = open(path.c_str(), O_CLOEXEC | O_RDWR | (create ? O_CREAT : 0), 0600); + if (!fd && (create || errno != ENOENT)) + throw SysError(format("opening lock file '%1%'") % path); - return fd; + return fd; } - -void deleteLockFile(const Path & path, int fd) -{ - /* Get rid of the lock file. Have to be careful not to introduce - races. Write a (meaningless) token to the file to indicate to - other processes waiting on this lock that the lock is stale - (deleted). */ - unlink(path.c_str()); - writeFull(fd, "d"); - /* Note that the result of unlink() is ignored; removing the lock - file is an optimisation, not a necessity. */ +void deleteLockFile(const Path& path, int fd) { + /* Get rid of the lock file. Have to be careful not to introduce + races. Write a (meaningless) token to the file to indicate to + other processes waiting on this lock that the lock is stale + (deleted). */ + unlink(path.c_str()); + writeFull(fd, "d"); + /* Note that the result of unlink() is ignored; removing the lock + file is an optimisation, not a necessity. */ } - -bool lockFile(int fd, LockType lockType, bool wait) -{ - int type; - if (lockType == ltRead) type = LOCK_SH; - else if (lockType == ltWrite) type = LOCK_EX; - else if (lockType == ltNone) type = LOCK_UN; - else abort(); - - if (wait) { - while (flock(fd, type) != 0) { - checkInterrupt(); - if (errno != EINTR) - throw SysError(format("acquiring/releasing lock")); - else - return false; - } - } else { - while (flock(fd, type | LOCK_NB) != 0) { - checkInterrupt(); - if (errno == EWOULDBLOCK) return false; - if (errno != EINTR) - throw SysError(format("acquiring/releasing lock")); - } +bool lockFile(int fd, LockType lockType, bool wait) { + int type; + if (lockType == ltRead) + type = LOCK_SH; + else if (lockType == ltWrite) + type = LOCK_EX; + else if (lockType == ltNone) + type = LOCK_UN; + else + abort(); + + if (wait) { + while (flock(fd, type) != 0) { + checkInterrupt(); + if (errno != EINTR) + throw SysError(format("acquiring/releasing lock")); + else + return false; } + } else { + while (flock(fd, type | LOCK_NB) != 0) { + checkInterrupt(); + if (errno == EWOULDBLOCK) return false; + if (errno != EINTR) throw SysError(format("acquiring/releasing lock")); + } + } - return true; + return true; } +PathLocks::PathLocks() : deletePaths(false) {} -PathLocks::PathLocks() - : deletePaths(false) -{ +PathLocks::PathLocks(const PathSet& paths, const string& waitMsg) + : deletePaths(false) { + lockPaths(paths, waitMsg); } +bool PathLocks::lockPaths(const PathSet& paths, const string& waitMsg, + bool wait) { + assert(fds.empty()); -PathLocks::PathLocks(const PathSet & paths, const string & waitMsg) - : deletePaths(false) -{ - lockPaths(paths, waitMsg); -} + /* Note that `fds' is built incrementally so that the destructor + will only release those locks that we have already acquired. */ + /* Acquire the lock for each path in sorted order. This ensures + that locks are always acquired in the same order, thus + preventing deadlocks. */ + for (auto& path : paths) { + checkInterrupt(); + Path lockPath = path + ".lock"; -bool PathLocks::lockPaths(const PathSet & paths, - const string & waitMsg, bool wait) -{ - assert(fds.empty()); - - /* Note that `fds' is built incrementally so that the destructor - will only release those locks that we have already acquired. */ - - /* Acquire the lock for each path in sorted order. This ensures - that locks are always acquired in the same order, thus - preventing deadlocks. */ - for (auto & path : paths) { - checkInterrupt(); - Path lockPath = path + ".lock"; - - debug(format("locking path '%1%'") % path); - - AutoCloseFD fd; - - while (1) { - - /* Open/create the lock file. */ - fd = openLockFile(lockPath, true); - - /* Acquire an exclusive lock. */ - if (!lockFile(fd.get(), ltWrite, false)) { - if (wait) { - if (waitMsg != "") printError(waitMsg); - lockFile(fd.get(), ltWrite, true); - } else { - /* Failed to lock this path; release all other - locks. */ - unlock(); - return false; - } - } - - debug(format("lock acquired on '%1%'") % lockPath); - - /* Check that the lock file hasn't become stale (i.e., - hasn't been unlinked). */ - struct stat st; - if (fstat(fd.get(), &st) == -1) - throw SysError(format("statting lock file '%1%'") % lockPath); - if (st.st_size != 0) - /* This lock file has been unlinked, so we're holding - a lock on a deleted file. This means that other - processes may create and acquire a lock on - `lockPath', and proceed. So we must retry. */ - debug(format("open lock file '%1%' has become stale") % lockPath); - else - break; - } + debug(format("locking path '%1%'") % path); - /* Use borrow so that the descriptor isn't closed. */ - fds.push_back(FDPair(fd.release(), lockPath)); - } + AutoCloseFD fd; - return true; -} + while (1) { + /* Open/create the lock file. */ + fd = openLockFile(lockPath, true); + + /* Acquire an exclusive lock. */ + if (!lockFile(fd.get(), ltWrite, false)) { + if (wait) { + if (waitMsg != "") printError(waitMsg); + lockFile(fd.get(), ltWrite, true); + } else { + /* Failed to lock this path; release all other + locks. */ + unlock(); + return false; + } + } + + debug(format("lock acquired on '%1%'") % lockPath); + + /* Check that the lock file hasn't become stale (i.e., + hasn't been unlinked). */ + struct stat st; + if (fstat(fd.get(), &st) == -1) + throw SysError(format("statting lock file '%1%'") % lockPath); + if (st.st_size != 0) + /* This lock file has been unlinked, so we're holding + a lock on a deleted file. This means that other + processes may create and acquire a lock on + `lockPath', and proceed. So we must retry. */ + debug(format("open lock file '%1%' has become stale") % lockPath); + else + break; + } + /* Use borrow so that the descriptor isn't closed. */ + fds.push_back(FDPair(fd.release(), lockPath)); + } -PathLocks::~PathLocks() -{ - try { - unlock(); - } catch (...) { - ignoreException(); - } + return true; } +PathLocks::~PathLocks() { + try { + unlock(); + } catch (...) { + ignoreException(); + } +} -void PathLocks::unlock() -{ - for (auto & i : fds) { - if (deletePaths) deleteLockFile(i.second, i.first); +void PathLocks::unlock() { + for (auto& i : fds) { + if (deletePaths) deleteLockFile(i.second, i.first); - if (close(i.first) == -1) - printError( - format("error (ignored): cannot close lock file on '%1%'") % i.second); + if (close(i.first) == -1) + printError(format("error (ignored): cannot close lock file on '%1%'") % + i.second); - debug(format("lock released on '%1%'") % i.second); - } + debug(format("lock released on '%1%'") % i.second); + } - fds.clear(); + fds.clear(); } - -void PathLocks::setDeletion(bool deletePaths) -{ - this->deletePaths = deletePaths; +void PathLocks::setDeletion(bool deletePaths) { + this->deletePaths = deletePaths; } - -} +} // namespace nix |