1 files changed, 147 insertions, 0 deletions
diff --git a/cherrypy/lib/lockfile.py b/cherrypy/lib/lockfile.py
new file mode 100644
index 00000000..b9d8e027
--- /dev/null
+++ b/cherrypy/lib/lockfile.py
@@ -0,0 +1,147 @@
+"""
+Platform-independent file locking. Inspired by and modeled after zc.lockfile.
+"""
+
+import os
+
+try:
+    import msvcrt
+except ImportError:
+    pass
+
+try:
+    import fcntl
+except ImportError:
+    pass
+
+
+class LockError(Exception):
+
+    "Could not obtain a lock"
+
+    msg = "Unable to lock %r"
+
+    def __init__(self, path):
+        super(LockError, self).__init__(self.msg % path)
+
+
+class UnlockError(LockError):
+
+    "Could not release a lock"
+
+    msg = "Unable to unlock %r"
+
+
+# first, a default, naive locking implementation
+class LockFile(object):
+
+    """
+    A default, naive locking implementation. Always fails if the file
+    already exists.
+    """
+
+    def __init__(self, path):
+        self.path = path
+        try:
+            fd = os.open(path, os.O_CREAT | os.O_WRONLY | os.O_EXCL)
+        except OSError:
+            raise LockError(self.path)
+        os.close(fd)
+
+    def release(self):
+        os.remove(self.path)
+
+    def remove(self):
+        pass
+
+
+class SystemLockFile(object):
+
+    """
+    An abstract base class for platform-specific locking.
+    """
+
+    def __init__(self, path):
+        self.path = path
+
+        try:
+            # Open lockfile for writing without truncation:
+            self.fp = open(path, 'r+')
+        except IOError:
+            # If the file doesn't exist, IOError is raised; Use a+ instead.
+            # Note that there may be a race here. Multiple processes
+            # could fail on the r+ open and open the file a+, but only
+            # one will get the the lock and write a pid.
+            self.fp = open(path, 'a+')
+
+        try:
+            self._lock_file()
+        except:
+            self.fp.seek(1)
+            self.fp.close()
+            del self.fp
+            raise
+
+        self.fp.write(" %s\n" % os.getpid())
+        self.fp.truncate()
+        self.fp.flush()
+
+    def release(self):
+        if not hasattr(self, 'fp'):
+            return
+        self._unlock_file()
+        self.fp.close()
+        del self.fp
+
+    def remove(self):
+        """
+        Attempt to remove the file
+        """
+        try:
+            os.remove(self.path)
+        except:
+            pass
+
+    #@abc.abstract_method
+    # def _lock_file(self):
+    #    """Attempt to obtain the lock on self.fp. Raise LockError if not
+    #    acquired."""
+
+    def _unlock_file(self):
+        """Attempt to obtain the lock on self.fp. Raise UnlockError if not
+        released."""
+
+
+class WindowsLockFile(SystemLockFile):
+
+    def _lock_file(self):
+        # Lock just the first byte
+        try:
+            msvcrt.locking(self.fp.fileno(), msvcrt.LK_NBLCK, 1)
+        except IOError:
+            raise LockError(self.fp.name)
+
+    def _unlock_file(self):
+        try:
+            self.fp.seek(0)
+            msvcrt.locking(self.fp.fileno(), msvcrt.LK_UNLCK, 1)
+        except IOError:
+            raise UnlockError(self.fp.name)
+
+if 'msvcrt' in globals():
+    LockFile = WindowsLockFile
+
+
+class UnixLockFile(SystemLockFile):
+
+    def _lock_file(self):
+        flags = fcntl.LOCK_EX | fcntl.LOCK_NB
+        try:
+            fcntl.flock(self.fp.fileno(), flags)
+        except IOError:
+            raise LockError(self.fp.name)
+
+    # no need to implement _unlock_file, it will be unlocked on close()
+
+if 'fcntl' in globals():
+    LockFile = UnixLockFile