WinInet 和 InternetOpen

Question

文档指出可以多次调用 InternetOpen 而不会出现任何问题。我的问题是我应该多次调用它返回的句柄上的 InternetCloseHandle 吗？

例如，我有一个 class，我称之为 CAPIRequestContext，它有一个由 InternetOpen 返回的句柄。我的每一个请求都有它自己的副本。现在，我在析构函数中调用了 InternetCloseHandle，因此它被调用了多次。

我想知道以下情况是否会导致问题：线程 A 创建一个 CAPIRequestObject 调用 InternetOpen 并存储句柄。线程 B 做同样的事情，但在线程 A 退出之前超出范围，因此线程 B 在它自己的 CAPIRequestObject 中调用析构函数，它在 InternetOpen 返回的句柄上调用 InternetCloseHandle。

我是否应该在 class 的析构函数中删除对 InternetCloseHandle 的调用？至少对于 InternetHandle？我假设我应该为 HttpOpenRequest 返回的句柄调用 InternetCloseHandle。

我对 InternetConnect 返回的句柄有类似的疑问。这些句柄是共享的吗？

这是一些示例代码，减去一些我认为与问题无关的外部代码：

class CAPIClient;
class CAPIRequest
{
public:
     CAPIRequestContext()
     {
         m_hConn = NULL;
         m_hInternet = NULL;
         m_hRequest = NULL;
     }

     ~CAPIRequestContext()
     {
         if (m_hRequest) InternetCloseHandle(m_hRequest);
         if (m_hConn) InternetCloseHandle(m_hConn);
         if (m_hInternet) InternetCloseHandle(m_hInternet);
     }

     bool Init(const CAPIClient &client, const std::string &uri, const std::string &method)
     {
          ATLASSERT(!(m_hInternet || m_hConn || m_hRequest));
          if (m_hInternet || m_hConn || m_hRequest) throw std::exception("Cannot init request more than once.");

          bool success = false;
          m_AuthToken = *client.m_pAuthToken;
          URI = uri;
          m_hInternet = InternetOpen("MyApp", INTERNET_OPEN_TYPE_PRECONFIG, NULL, NULL, 0);
DWORD requestTimeout = 60 * 1000; // Set timeout to 60 seconds instead of 30

          if (m_hInternet)
          {  
                InternetSetOption(m_hInternet, INTERNET_OPTION_RECEIVE_TIMEOUT, &requestTimeout, sizeof(requestTimeout));
                m_hConn = InternetConnect(m_hInternet, (LPSTR)client.m_host.c_str(), client.m_port, NULL, NULL, INTERNET_SERVICE_HTTP, 0, (DWORD_PTR)this);
                if (m_hConn) {
                      m_hRequest = HttpOpenRequest(m_hConn, method.c_str(), uri.c_str(), "HTTP/1.1", NULL, NULL, client.GetOpenRequestFlags(), 0);
                }
                if (m_hRequest)
                {
                    success = true;
                }
          }
       return success;
     }      
}

    // There are additional calls like 
    // SendRequest
    // GetData
    // GetFullResponse

private:
     // Added these methods to make sure I'm not copying the handles
enter code here
     CAPIRequestContext(const CAPIRequestContext &other) = delete;
     CAPIRequestContext& operator=(const CAPIRequestContext& other) = delete;

private:
      HINTERNET m_hInternet;
      HINTERNET m_hConn;
      HINTERNET m_hRequest;

}

Answer 1

The documentation states that InternetOpen can be called multiple times without any issues. My question though is should I be calling InternetCloseHandle on handle returned by it multiple times?

是的，如 InternetOpen() 文档所述：

After the calling application has finished using the HINTERNET handle returned by InternetOpen, it must be closed using the InternetCloseHandle function.

For example, I have a class I call CAPIRequestContext, which has a handle which is returned by InternetOpen. Each one of my requests has it's own copy. Right now, I call InternetCloseHandle in the destructor, so it gets called multiple times.

如果 class 的每个实例调用 InternetOpen()，或者以其他方式获得唯一 HINTERNET.

的所有权，那将是一个正确的实现

但是，请注意这样的 class 需要实现 Rule of Three。基本上，如果你必须提供一个析构函数来释放资源，你还需要提供一个复制构造函数和复制赋值运算符。

但是，你不能在同一个 HINTERNET 上多次调用 InternetCloseHandle()，所以你不能有多个 CAPIRequestContext 使用同一个 HINTERNET 和所有其中调用 InternetCloseHandle()¹。因此，您的复制构造函数和复制赋值运算符必须：

从正在复制的来源 CAPIRequestContext 获取 HINTERNET 的所有权。
完全禁用以防止将一个 CAPIRequestContext 复制到另一个。

在你的情况下，我会选择#2。

¹：您需要一个实例标志，指示哪个实例可以调用它，哪些不能。但是这样class设计的不好。如果您需要共享一个 HINTERNET，您应该改为实现引用计数语义，例如 std::shared_ptr.

提供的

I'm wondering if the following could cause issues: Thread A creates a CAPIRequestObject which calls InternetOpen and stores the handle. Thread B does the same, but then goes out of scope before Thread A exits, so Thread B calls the destructor in it's own CAPIRequestObject, which calls InternetCloseHandle on the handle returned by InternetOpen.

这是绝对安全的，前提是每个 CAPIRequestObject 都有自己的 HINTERNET。

Should I remove the call to InternetCloseHandle in the destructors of my class?

否，如果每个 class 实例都拥有唯一的 HINTERNET。

I assume I should call InternetCloseHandle for the handle returned by HttpOpenRequest.

是的，如 HttpOpenRequest() 文档中所述：

After the calling application has finished using the HINTERNET handle returned by HttpOpenRequest, it must be closed using the InternetCloseHandle function.

I have similar questions regarding the handle returned by InternetConnect. Are these handles shared?

每个 HINTERNET 必须单独关闭。

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