Windows 命名信号量未被锁定

Question

我正在开发 C++ class 并调用 Windows API C 库。

我正在使用信号量执行任务，假设我有两个进程：

ProcessA 有两个信号量：

Global\processA_receiving_semaphore

Global\processA_waiting_semaphore

ProcessB 有两个信号量：

Global\processB_receiving_semaphore

Global\processB_waiting_semaphore

我在每个进程中有两个线程：

正在进程A中发送线程：

Wait on "Global\processB_waiting_semaphore"

// do something

Signal "Global\processB_receiving_semaphore"

processB 上的接收线程：

Wait on "Global\processB_receiving_semaphore"

// do something

Signal "Global\processB_waiting_semaphore

我删除了所有发布“Global\processB_waiting_semaphore”的代码，但它仍然可以获取。在那个信号量上调用 WaitForSingleObject 总是 returns 成功等待并立即。我尝试将超时时间设置为 0，它仍然在没有释放信号量的情况下获取信号量。

接收信号量有initial count = 0和max count = 1，而等待信号量有initial count = 1和max count = 1。

在接收信号量上调用 WaitForSingleObject 效果很好，并且会阻塞直到被其他进程释放。问题出在等待信号量上，我不明白为什么。代码非常大，我已经确保信号量的名称设置正确。

这是一个常见问题吗？如果您需要更多解释，请发表评论，我将修改 post.

编辑：添加的代码：

接收器信号量：

bool intr_process_comm::create_rcvr_semaphores()
{
  std::cout << "\n  Creating semaphore: " << "Global\" << this_name << "_rcvr_sem";
  rcvr_sem = CreateSemaphore(NULL, 0, 1, ("Global\" + this_name + "_rcvr_sem").c_str());

  std::cout << "\n  Creating semaphore: " << "Global\" << this_name << "_wait_sem";
  wait_sem = CreateSemaphore(NULL, 1, 1, ("Global\" + this_name + "_wait_sem").c_str());

  return (rcvr_sem && wait_sem);
}

发件人信号量：

// this sender connects to the wait semaphore in the target process
sndr_sem = OpenSemaphore(SEMAPHORE_MODIFY_STATE, FALSE, ("Global\" + target_name + "_wait_sem").c_str());
// this target connects to the receiver semaphore in the target process
trgt_sem = OpenSemaphore(SEMAPHORE_MODIFY_STATE, FALSE, ("Global\" + target_name + "_rcvr_sem").c_str());

DWORD intr_process_locking::wait(unsigned long period)
{
   return WaitForSingleObject(sndr_sem, period);
}

void intr_process_locking::signal()
{
   ReleaseSemaphore(trgt_sem, 1, 0);
}

接收线程函数：

void intr_process_comm::rcvr_thread_proc()
{
  while (conn_state == intr_process_comm::opened) {
    try {
      // wait on rcvr_semaphore for an infinite time
      WaitForSingleObject(rcvr_sem, INFINITE);
      if (inner_release) // if the semaphore was released within this process
        return;
      // once signaled by another process, get the message
      std::string msg_str((LPCSTR)hmf_mapview);
      // signal one of the waiters that want to put messages 
      // in this process's memory area
      // 
      // this doesn't change ANYTHING in execution, commented or not..
      //ReleaseSemaphore(wait_sem, 1, 0);

      // put this message in this process's queue
      Msg msg = Msg::from_xml(msg_str);
      if (msg.command == "connection")
        process_connection_message(msg);
  
      in_messages.enQ(msg);
      //std::cout << "\n  Message: \n"<< msg << "\n";
    }
    catch (std::exception e) {
      std::cout << "\n  Ran into trouble getting the message. Details: " << e.what();
    }
  }
}

发送线程函数：

void intr_process_comm::sndr_thread_proc()
{
  while (conn_state == intr_process_comm::opened ||
    (conn_state == intr_process_comm::closing && out_messages.size() > 0)
    ) {
    // pull a message out of the queue
    Msg msg = out_messages.deQ();

    if (connections.find(msg.destination) == connections.end())
      connections[msg.destination].connect(msg.destination);

    if (connections[msg.destination].connect(msg.destination)
      != intr_process_locking::state::opened) {
      blocked_messages[msg.destination].push_back(msg);
      continue;
    }

    // THIS ALWAYS GETS GETS WAIT_OBJECT_0 RESULT
    DWORD wait_result = connections[msg.destination].wait(wait_timeout);
    if (wait_result == WAIT_TIMEOUT) {  // <---- THIS IS NEVER TRUE
      out_messages.enQ(msg);
      continue;
    }
    // do things here
    // release the receiver semaphore in the other process
    connections[msg.destination].signal();
  }
}

澄清一些事情：

发件人中的

trgt_sem 是收件人中的 rcvr_sem。

发送方的

`sndr_sem'是接收方的'wait_sem"。

Answer 1

如果将超时设置为 0 WaitForSingleObject 将始终 return 立即，成功的 WaitForSingleObject 将 return WAIT_OBJECT_0 （恰好值为 0），WFSO 不像大多数由非零 return.

指示成功的 API

Answer 2

调用 WaitForSingleObject 一些句柄：

The handle must have the SYNCHRONIZE access right.

但您打开信号灯时只有 SEMAPHORE_MODIFY_STATE 访问权限。使用此访问可能调用 ReleaseSemaphore（此句柄必须具有 SEMAPHORE_MODIFY_STATE 访问权限）但调用 WaitForSingleObject 失败，结果为 WAIT_FAILED .在此之后调用 GetLastError() 必须 return ERROR_ACCESS_DENIED。

因此，如果我们想同时调用 ReleaseSemaphore 和任何等待函数 - 我们需要对句柄具有 SEMAPHORE_MODIFY_STATE | SYNCHRONIZE 访问权限。所以需要用代码

打开

OpenSemaphore(SEMAPHORE_MODIFY_STATE|SYNCHRONIZE, )

当然还要经常检查 api return 值和错误代码可以节省很多时间

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