自然的方法是实现一个完成例程并调用ReadDirectoryChangesW使用它的重叠模式。以下示例显示了执行此操作的方法：
RDCW_CALLBACK_F = ctypes.WINFUNCTYPE(None, ctypes.wintypes.DWORD, ctypes.wintypes.DWORD, ctypes.POINTER(OVERLAPPED))
首先，创建一个 WINFUNCTYPE 工厂，该工厂将用于从 python 方法生成（可从 Windows API 调用）类似 C 的函数。在这种情况下，没有返回值和3个参数对应
VOID CALLBACK FileIOCompletionRoutine(
_In_ DWORD dwErrorCode,
_In_ DWORD dwNumberOfBytesTransfered,
_Inout_ LPOVERLAPPED lpOverlapped
);
FileIOCompletionRoutine标头。
回调引用以及重叠结构需要添加到ReadDirectoryChangesW参数列表中：
ReadDirectoryChangesW = ctypes.windll.kernel32.ReadDirectoryChangesW
ReadDirectoryChangesW.restype = ctypes.wintypes.BOOL
ReadDirectoryChangesW.errcheck = _errcheck_bool
ReadDirectoryChangesW.argtypes = (
ctypes.wintypes.HANDLE, # hDirectory
LPVOID, # lpBuffer
ctypes.wintypes.DWORD, # nBufferLength
ctypes.wintypes.BOOL, # bWatchSubtree
ctypes.wintypes.DWORD, # dwNotifyFilter
ctypes.POINTER(ctypes.wintypes.DWORD), # lpBytesReturned
ctypes.POINTER(OVERLAPPED), # lpOverlapped
RDCW_CALLBACK_F # FileIOCompletionRoutine # lpCompletionRoutine
)
从这里，我们准备好执行重叠的系统调用。这是一个简单的调用 bacl 只是用于测试一切正常：
def dir_change_callback(dwErrorCode,dwNumberOfBytesTransfered,p):
print("dir_change_callback! PID:" + str(os.getpid()))
print("CALLBACK THREAD: " + str(threading.currentThread()))
准备并执行呼叫：
event_buffer = ctypes.create_string_buffer(BUFFER_SIZE)
nbytes = ctypes.wintypes.DWORD()
overlapped_read_dir = OVERLAPPED()
call2pass = RDCW_CALLBACK_F(dir_change_callback)
hand = get_directory_handle(os.path.abspath("/test/"))
def docall():
ReadDirectoryChangesW(hand, ctypes.byref(event_buffer),
len(event_buffer), False,
WATCHDOG_FILE_NOTIFY_FLAGS,
ctypes.byref(nbytes),
ctypes.byref(overlapped_read_dir), call2pass)
print("Waiting!")
docall()
如果您将所有这些代码加载并执行到DreamPie交互式 shell 中，您可以检查系统调用是否完成以及回调是否执行，从而在c:\test目录下第一次更改完成后打印线程和 pid 编号。此外，您会注意到它们与主线程和进程相同：尽管事件是由单独的线程引发的，但回调在与我们的主程序相同的进程和线程中运行，因此提供了不希望的行为：
lck = threading.Lock()
def dir_change_callback(dwErrorCode,dwNumberOfBytesTransfered,p):
print("dir_change_callback! PID:" + str(os.getpid()))
print("CALLBACK THREAD: " + str(threading.currentThread()))
...
...
...
lck.acquire()
print("Waiting!")
docall()
lck.acquire()
该程序将锁定主线程并且回调永远不会执行。我尝试了许多同步工具，甚至 Windows API 信号量总是得到相同的行为，所以最后，我决定在使用python 库ReadDirectoryChangesW管理和同步的单独进程中使用同步配置来实现异步调用：multiprocessing
调用get_directory_handle不会返回由 Windows API 提供的句柄编号，而是由winapi库管理的句柄编号，为此我实现了一个句柄生成器：
class FakeHandleFactory():
_hl = threading.Lock()
_next = 0
@staticmethod
def next():
FakeHandleFactory._hl.acquire()
ret = FakeHandleFactory._next
FakeHandleFactory._next += 1
FakeHandleFactory._hl.release()
return ret
每个生成的句柄都必须与文件系统路径全局关联：
handle2file = {}
现在，每次调用都read_directory_changes将生成ReadDirectoryRequest（派生自multiprocessing.Process）对象：
class ReadDirectoryRequest(multiprocessing.Process):
def _perform_and_wait4request(self, path, recursive, event_buffer, nbytes):
hdl = CreateFileW(path, FILE_LIST_DIRECTORY, WATCHDOG_FILE_SHARE_FLAGS,
None, OPEN_EXISTING, WATCHDOG_FILE_FLAGS, None)
#print("path: " + path)
aux_buffer = ctypes.create_string_buffer(BUFFER_SIZE)
aux_n = ctypes.wintypes.DWORD()
#print("_perform_and_wait4request! PID:" + str(os.getpid()))
#print("CALLBACK THREAD: " + str(threading.currentThread()) + "\n----------")
try:
ReadDirectoryChangesW(hdl, ctypes.byref(aux_buffer),
len(event_buffer), recursive,
WATCHDOG_FILE_NOTIFY_FLAGS,
ctypes.byref(aux_n), None, None)
except WindowsError as e:
print("!" + str(e))
if e.winerror == ERROR_OPERATION_ABORTED:
nbytes = 0
event_buffer = []
else:
nbytes = 0
event_buffer = []
# Python 2/3 compat
nbytes.value = aux_n.value
for i in xrange(self.int_class(aux_n.value)):
event_buffer[i] = aux_buffer[i]
CloseHandle(hdl)
try:
self.lck.release()
except:
pass
def __init__(self, handle, recursive):
buffer = ctypes.create_string_buffer(BUFFER_SIZE)
self.event_buffer = multiprocessing.Array(ctypes.c_char, buffer)
self.nbytes = multiprocessing.Value(ctypes.wintypes.DWORD, 0)
targetPath = handle2file.get(handle, None)
super(ReadDirectoryRequest, self).__init__(target=self._perform_and_wait4request, args=(targetPath, recursive, self.event_buffer, self.nbytes))
self.daemon = True
self.lck = multiprocessing.Lock()
self.result = None
try:
self.int_class = long
except NameError:
self.int_class = int
if targetPath is None:
self.result = ([], -1)
def CancelIo(self):
try:
self.result = ([], 0)
self.lck.release()
except:
pass
def read_changes(self):
#print("read_changes! PID:" + str(os.getpid()))
#print("CALLBACK THREAD: " + str(threading.currentThread()) + "\n----------")
if self.result is not None:
raise Exception("ReadDirectoryRequest object can be used only once!")
self.lck.acquire()
self.start()
self.lck.acquire()
self.result = (self.event_buffer, self.int_class(self.nbytes.value))
return self.result
此类指定Process提供一个执行系统调用并等待直到（或）的进程：
- 已引发更改事件。
- 主线程通过调用
ReadDirectoryRequest对象CancelIo方法取消请求。
注意：
- 获取目录句柄
- close_directory_handle
- 读取目录更改
角色现在用于管理请求。为此，需要线程锁和辅助数据结构：
rqIndexLck = threading.Lock() # Protects the access to `rqIndex`
rqIndex = {} # Maps handles to request objects sets.
获取目录句柄
def get_directory_handle(path):
rqIndexLck.acquire()
ret = FakeHandleFactory.next()
handle2file[ret] = path
rqIndexLck.release()
return ret
close_directory_handle
def close_directory_handle(handle):
rqIndexLck.acquire()
rqset4handle = rqIndex.get(handle, None)
if rqset4handle is not None:
for rq in rqset4handle:
rq.CancelIo()
del rqIndex[handle]
if handle in handle2file:
del handle2file[handle]
rqIndexLck.release()
最后但同样重要的是：read_directory_changes
def read_directory_changes(handle, recursive):
rqIndexLck.acquire()
rq = ReadDirectoryRequest(handle, recursive)
set4handle = None
if handle in rqIndex:
set4handle = rqIndex[handle]
else:
set4handle = set()
rqIndex[handle] = set4handle
set4handle.add(rq)
rqIndexLck.release()
ret = rq.read_changes()
rqIndexLck.acquire()
if rq in set4handle:
set4handle.remove(rq)
rqIndexLck.release()
return ret