提交 #1

developtools/integration_verification/DeployDevice/resource/common/portalocker.py

@@ -0,0 +1,97 @@
+#encoding=utf-8
+import os
+import time
+import errno
+ 
+class FileLockException(Exception):
+    pass
+
+class FileLock(object):
+    """ A file locking mechanism that has context-manager support so 
+        you can use it in a with statement. This should be relatively cross
+        compatible as it doesn't rely on msvcrt or fcntl for the locking.
+    """
+
+
+    def __init__(self, timeout=7200, delay=30):
+        """ Prepare the file locker. Specify the file to lock and optionally
+            the maximum timeout and the delay between each attempt to lock.
+        """
+        self.is_locked = False
+        self.timeout = timeout
+        self.delay = delay
+
+    def _setLockFileName(self, file_name):
+        self.lockfile = file_name
+
+    def acquire(self):
+        """ Acquire the lock, if possible. If the lock is in use, it check again
+            every `wait` seconds. It does this until it either gets the lock or
+            exceeds `timeout` number of seconds, in which case it throws 
+            an exception.
+        """
+        start_time = time.time()
+        if os.path.isfile(self.lockfile):
+            try:
+                mark_file_mtime = os.path.getmtime(self.lockfile)
+                if (start_time - mark_file_mtime > self.timeout):
+                    os.remove(self.lockfile)
+            except Exception as e:
+                print("the lock file is locked by other process")
+
+        while True:
+            try:
+                #open file , other application can't open it
+                self.fd = os.open(self.lockfile, os.O_CREAT|os.O_EXCL|os.O_RDWR)
+                break
+            except OSError as e:
+                if e.errno != errno.EEXIST:
+                    raise 
+                if (time.time() - start_time) >= self.timeout:
+                    raise FileLockException("Timeout occured.")
+                time.sleep(self.delay)
+        self.is_locked = True
+
+
+    def release(self):
+        """ Get rid of the lock by deleting the lockfile. 
+            When working in a `with` statement, this gets automatically 
+            called at the end.
+        """
+        #
+        if self.is_locked :
+            os.close(self.fd)
+            os.unlink(self.lockfile)
+            self.is_locked = False
+
+    def lockFile(self, file_name):
+        """ Activated when used in the with statement. 
+            Should automatically acquire a lock to be used in the with block.
+        """
+        self._setLockFileName(file_name)
+        if not self.is_locked:
+            self.acquire()
+        return self
+
+    def releaseFile(self):
+        """ Activated at the end of the with statement.
+            It automatically releases the lock if it isn't locked.
+        """
+        if self.is_locked:
+            self.release()
+
+    def __del__(self):
+        """ Make sure that the FileLock instance doesn't leave a lockfile
+            lying around.
+        """
+        self.release()
+
+
+
+#用法比较有意思，使用with关键字。对with关键字来说，FileLock类先执行__enter__函数，然后，执行with块里的那些代码，执行完了之后，再执行__exit__函数，等价于相当于如下形式：
+#try:
+#    执行 __enter__的内容
+#    执行 with_block.
+#finally:
+#    执行 __exit__内容
+#FileLock在__enter__函数独占式创建或打开一个文件，这个文件不会被其他程序或者进程再次创建或者打开，由此形成lock，执行完代码，在__exit__里，关闭并删除文件