Question

我正在使用CreateFile()打开一个串口。我有一个测试用例（太复杂而无法重新分发），导致CreateFile()返回INVALID_HANDLE_VALUE和GetLastError()返回ERROR_SUCCESS。通过它的外观，只有当一个线程在另一个端口关闭它的同一时间打开端口时，才会出现此错误。打开端口的线程遇到了这个问题。

我不知道这是否会有所不同，但稍后在代码中我使用CreateIoCompletionPort将端口与CompletionPort相关联。

这是我的代码：

HANDLE port = CreateFile(L"\\\\.\\COM1",
                         GENERIC_READ | GENERIC_WRITE,
                         0,                    // must be opened with exclusive-access
                         0,                    // default security attributes
                         OPEN_EXISTING,        // must use OPEN_EXISTING
                         FILE_FLAG_OVERLAPPED, // overlapped I/O
                         0);                   // hTemplate must be NULL for comm devices
if (port == INVALID_HANDLE_VALUE)
{
    DWORD errorCode = GetLastError();
    cerr << L"CreateFile() failed with error: " << errorCode << endl;
}

我很确定这种事情不应该发生。我做错了吗？如何让API返回正确的结果？

更多细节：此代码来自我开发的串口库：JPeripheral

这是实际的（未经过规范化的）源代码：

JLong SerialChannel::nativeOpen(String name)
{
    cerr << "nativeOpen(" << name << ")" << endl;
    wstring nameWstring = name;
    HANDLE port = CreateFile((L"\\\\.\\" + nameWstring).c_str(),
        GENERIC_READ | GENERIC_WRITE,
        0,                                          // must be opened with exclusive-access
        0,                                          // default security attributes
        OPEN_EXISTING,                  // must use OPEN_EXISTING
        FILE_FLAG_OVERLAPPED,       // overlapped I/O
        0);                                         // hTemplate must be NULL for comm devices
    cerr << "nativeOpen.afterCreateFile(" << name << ")" << endl;
    cerr << "port: " << port << ", errorCode: " << GetLastError() << endl;
    if (port == INVALID_HANDLE_VALUE)
    {
        DWORD errorCode = GetLastError();

        switch (errorCode)
        {
            case ERROR_FILE_NOT_FOUND:
                throw PeripheralNotFoundException(jace::java_new<PeripheralNotFoundException>(name, Throwable()));
            case ERROR_ACCESS_DENIED:
            case ERROR_SHARING_VIOLATION:
                throw PeripheralInUseException(jace::java_new<PeripheralInUseException>(name, Throwable()));
            default:
            {
                throw IOException(jace::java_new<IOException>(L"CreateFile() failed with error: " +
                    getErrorMessage(GetLastError())));
            }
        }
    }

    // Associate the file handle with the existing completion port
    HANDLE completionPort = CreateIoCompletionPort(port, ::jperipheral::worker->completionPort, Task::COMPLETION, 0);
    if (completionPort==0)
    {
        throw AssertionError(jace::java_new<AssertionError>(L"CreateIoCompletionPort() failed with error: " +
            getErrorMessage(GetLastError())));
    }
    cerr << "nativeOpen.afterCompletionPort(" << name << ")" << endl;

    // Bind the native serial port to Java serial port
    SerialPortContext* result = new SerialPortContext(port);
    cerr << "nativeOpen.afterContext(" << name << ")" << endl;
    return reinterpret_cast<intptr_t>(result);
}

这是我得到的实际输出：

nativeOpen(COM1)
nativeOpen.afterCreateFile(COM1)
port: 00000374, errorCode: 0
nativeOpen.afterCompletionPort(COM1)
nativeOpen.afterContext(COM1)
[...]
nativeOpen(COM1)
nativeOpen.afterCreateFile(COM1)
port: FFFFFFFF, errorCode: 0
java.io.IOException: CreateFile() failed with error: The operation completed successfully.

Answer 1

 HANDLE port = CreateFile(...);
 cerr << "nativeOpen.afterCreateFile(" << name << ")" << endl;
 cerr << "port: " << port << ", errorCode: " << GetLastError() << endl;
 if (port == INVALID_HANDLE_VALUE)
 {
    DWORD errorCode = GetLastError();

cerr的输出调用引擎盖下的winapi调用。这将重置GetLastError（）返回的线程错误值。修正：

 HANDLE port = CreateFile(...);
 int err = GetLastError();
 // etc, use err instead...

CreateFile（）返回INVALID_HANDLE_VALUE，但GetLastError（）是ERROR_SUCCESS

1 个答案: