如果您不想在等待客戶端連接時阻塞,則可以在異步I/O模式下創建管道,在這種情況下,對ConnectNamedPipe()的調用需要一個事件對象,該對象將在客戶端連接。或者,您可以設置PIPE_NOWAIT並定期調用ConnectNamedPipe(),直到它成功爲止,但這是一項遺留功能,不鼓勵使用它。 (在大多數情況下,使用事件對象也會比輪詢效率高很多)
正如您發現的那樣,Windows允許您在沒有調用ConnectNamedPipe()的情況下離開,但由於此行爲未記錄,因此應該可能會被避免。同樣,調用ConnectNamedPipe()而不等待它成功重置管道的連接狀態的事實是未記錄的,不應該依賴於該事實。
根據要求,下面是一些真實世界的代碼,演示如何使用管道的服務器端。此代碼取自GUI應用程序,因此它使用異步I/O,但應該注意的是,它一次只與一個客戶端通信。 (這可能然而,可以在多線程,只有輕微的修改即可運行。)
void wait_for_object(HANDLE object)
{
DWORD dw;
MSG msg;
for (;;)
{
dw = MsgWaitForMultipleObjectsEx(1, &object, INFINITE, QS_ALLINPUT, 0);
if (dw == WAIT_OBJECT_0) break;
if (dw == WAIT_OBJECT_0 + 1)
{
while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) DispatchMessage(&msg);
continue;
}
srvfail(L"sleep() messageloop", GetLastError());
}
}
HANDLE server_pipe;
HANDLE io_event;
void pipe_connection(void)
{
OVERLAPPED overlapped;
DWORD dw, err;
SecureZeroMemory(&overlapped, sizeof(overlapped));
overlapped.hEvent = io_event;
if (!ReadFile(server_pipe, input_buffer, sizeof(input_buffer) - 1, NULL, &overlapped))
{
err = GetLastError();
if (err == ERROR_IO_PENDING)
{
wait_for_object(io_event);
if (!GetOverlappedResult(server_pipe, &overlapped, &dw, FALSE))
{
srvfail(L"Read from pipe failed asynchronously.", GetLastError());
}
}
else
{
srvfail(L"Read from pipe failed synchronously.", GetLastError());
}
}
else
{
if (!GetOverlappedResult(server_pipe, &overlapped, &dw, FALSE))
{
srvfail(L"GetOverlappedResult failed reading from pipe.", GetLastError());
}
}
input_buffer[dw] = '\0';
process_command();
if (!WriteFile(server_pipe, &output_struct,
((char *)&output_struct.output_string - (char *)&output_struct) + output_struct.string_length,
NULL, &overlapped))
{
err = GetLastError();
if (err == ERROR_IO_PENDING)
{
wait_for_object(io_event);
if (!GetOverlappedResult(server_pipe, &overlapped, &dw, FALSE))
{
srvfail(L"Write to pipe failed asynchronously.", GetLastError());
}
}
else
{
srvfail(L"Write to pipe failed synchronously.", GetLastError());
}
}
else
{
if (!GetOverlappedResult(server_pipe, &overlapped, &dw, FALSE))
{
srvfail(L"GetOverlappedResult failed writing to pipe.", GetLastError());
}
}
if (!FlushFileBuffers(server_pipe)) srvfail(L"FlushFileBuffers failed.", GetLastError());
if (!DisconnectNamedPipe(server_pipe)) srvfail(L"DisconnectNamedPipe failed.", GetLastError());
}
void server(void)
{
OVERLAPPED overlapped;
DWORD err, dw;
// Create the named pipe
server_pipe = CreateNamedPipe(pipe_name, PIPE_ACCESS_DUPLEX | FILE_FLAG_FIRST_PIPE_INSTANCE | FILE_FLAG_OVERLAPPED, PIPE_TYPE_MESSAGE | PIPE_READMODE_MESSAGE, 1, buffer_size, buffer_size, 0, NULL);
if (server_pipe == INVALID_HANDLE_VALUE) srvfail(L"CreateNamedPipe failed.", GetLastError());
// Wait for connections
io_event = CreateEvent(NULL, FALSE, FALSE, NULL);
if (io_event == NULL) srvfail(L"CreateEvent(io_event) failed.", GetLastError());
for (;;)
{
SecureZeroMemory(&overlapped, sizeof(overlapped));
overlapped.hEvent = io_event;
if (!ConnectNamedPipe(server_pipe, &overlapped))
{
err = GetLastError();
if (err == ERROR_PIPE_CONNECTED)
{
pipe_connection();
}
else if (err == ERROR_IO_PENDING)
{
wait_for_object(io_event);
if (!GetOverlappedResult(server_pipe, &overlapped, &dw, FALSE))
{
srvfail(L"Pipe connection failed asynchronously.", GetLastError());
}
pipe_connection();
}
else
{
srvfail(L"Pipe connection failed synchronously.", GetLastError());
}
}
else
{
if (!GetOverlappedResult(server_pipe, &overlapped, &dw, FALSE))
{
srvfail(L"GetOverlappedResult failed connecting pipe.", GetLastError());
}
pipe_connection();
}
}
}
(此代碼已經從原來的編輯了下來,除去多餘的邏輯。我沒試過編譯編輯的版本,所以有可能是一些小問題。)
此行爲是未記錄的。最好等到ConnectNamedPipe()實際上成功後,通過輪詢或使用異步I/O。 (請參閱我的答案。) – 2016-03-06 23:03:19