使用pthreds与C ++中的线程通信

Question

There are two threads T1 and T2

class Sender{
      public:
      void sendMessage(); 
};

class Reciever{
      public:
      void getMessage(string msg); 
};

Consider Sender S is in Thread T1, Reciever R is in Thread T2 and now I need S.sendMessage() should communicate with object R to execute getMessage(string msg). So how can I do it... Producer and consumer approach might help but here it is a one-time requirement so is that really neede to maintain a common queue? please help me.

Answer 1

Condition variables are what you are looking for. They allow a thread to wait (blocking) for an event sent from another thread.

You correctly discerned that you do not need a producer-consumer queue if there is only one producer and only one consumer and only a single message is passed.

So, your receiver thread calls getMessage (which should either return a string, or take the string as a reference parameter), which internally waits for a condition variable. Then, in the sender thread, you notify the condition variable inside sendMessage. This wakes up the receiver thread.

Edit : Although you are asking a pthread-specific question, pthread has an equivalent of C++'s std::condition_variable. I recommend you use C++11's utilities instead of talking to pthreads directly, as they are easier to use.

Edit 2 : You cannot just make another thread execute some function. The only thing you can do between threads is communication, so if you want to have some reaction in another thread to something you do in your thread, the other thread has to be actively waiting for you to trigger this event (by notifying a condition variable or similar).

Answer 2

The standard way combines a std::queue with a mutex and a condition variable. The mutex is used by the condition variable and protects the queue. The receiver waits until the queue is not empty and then pops the message from the queue. The sender pushes the message onto the queue.

When only one type of message is needed, you can use a queue of messages, if not then make it dynamic by sending shared pointers to messages.