intermediate changes

ref:cde9a383711a11544ce7e107a78147fb96cc4029

1 files changed, 122 insertions, 0 deletions

diff --git a/library/python/filelock/__init__.py b/library/python/filelock/__init__.py
new file mode 100644
index 0000000000..f81ff67f37
--- /dev/null
+++ b/library/python/filelock/__init__.py
@@ -0,0 +1,122 @@
+import errno
+import logging
+import os
+import sys
+
+import library.python.windows
+
+logger = logging.getLogger(__name__)
+
+
+def set_close_on_exec(stream):
+    if library.python.windows.on_win():
+        library.python.windows.set_handle_information(stream, inherit=False)
+    else:
+        import fcntl
+        fcntl.fcntl(stream, fcntl.F_SETFD, fcntl.FD_CLOEXEC)
+
+
+class AbstractFileLock(object):
+
+    def __init__(self, path):
+        self.path = path
+
+    def acquire(self, blocking=True):
+        raise NotImplementedError
+
+    def release(self):
+        raise NotImplementedError
+
+    def __enter__(self):
+        self.acquire()
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.release()
+
+
+class _NixFileLock(AbstractFileLock):
+
+    def __init__(self, path):
+        super(_NixFileLock, self).__init__(path)
+        from fcntl import flock, LOCK_EX, LOCK_UN, LOCK_NB
+        self._locker = lambda lock, blocking: flock(lock, LOCK_EX if blocking else LOCK_EX | LOCK_NB)
+        self._unlocker = lambda lock: flock(lock, LOCK_UN)
+        self._lock = open(self.path, 'a')
+        set_close_on_exec(self._lock)
+
+    def acquire(self, blocking=True):
+        import errno
+        try:
+            self._locker(self._lock, blocking)
+        except IOError as e:
+            if e.errno in (errno.EAGAIN, errno.EACCES) and not blocking:
+                return False
+            raise
+        return True
+
+    def release(self):
+        self._unlocker(self._lock)
+
+    def __del__(self):
+        if hasattr(self, "_lock"):
+            self._lock.close()
+
+
+class _WinFileLock(AbstractFileLock):
+    """
+    Based on LockFile / UnlockFile from win32 API
+    https://msdn.microsoft.com/en-us/library/windows/desktop/aa365202(v=vs.85).aspx
+    """
+
+    _LOCKED_BYTES_NUM = 1
+
+    def __init__(self, path):
+        super(_WinFileLock, self).__init__(path)
+        self._lock = None
+        try:
+            with file(path, 'w') as lock_file:
+                lock_file.write(" " * self._LOCKED_BYTES_NUM)
+        except IOError as e:
+            if e.errno != errno.EACCES or not os.path.isfile(path):
+                raise
+
+    def acquire(self, blocking=True):
+        self._lock = open(self.path)
+        set_close_on_exec(self._lock)
+
+        import time
+        locked = False
+        while not locked:
+            locked = library.python.windows.lock_file(self._lock, 0, self._LOCKED_BYTES_NUM, raises=False)
+            if locked:
+                return True
+            if blocking:
+                time.sleep(.5)
+            else:
+                return False
+
+    def release(self):
+        if self._lock:
+            library.python.windows.unlock_file(self._lock, 0, self._LOCKED_BYTES_NUM, raises=False)
+            self._lock.close()
+            self._lock = None
+
+
+class FileLock(AbstractFileLock):
+
+    def __init__(self, path):
+        super(FileLock, self).__init__(path)
+
+        if sys.platform.startswith('win'):
+            self._lock = _WinFileLock(path)
+        else:
+            self._lock = _NixFileLock(path)
+
+    def acquire(self, blocking=True):
+        logger.debug('Acquiring filelock (blocking=%s): %s', blocking, self.path)
+        return self._lock.acquire(blocking)
+
+    def release(self):
+        logger.debug('Ensuring filelock released: %s', self.path)
+        return self._lock.release()