12-3.cpp

#include <iostream>
#include <boost/thread/thread.hpp>
#include <boost/thread/read_write_mutex.hpp>
#include <string>

template<typename T>
class Queue {
public:
   Queue( ) :  // Use a read/write mutex and give writers priority
      <userinput>rwMutex_(boost::read_write_scheduling_policy::writer_priority)</userinput> {}
  ~Queue( ) {}

   void enqueue(const T& x) {
      // Use a r/w lock since enqueue updates the state
      boost::read_write_mutex::scoped_write_lock writeLock(rwMutex_);
      list_.push_back(x);
   } 

   T dequeue( ) {
      // Again, use a write lock
      boost::read_write_mutex::scoped_write_lock writeLock(rwMutex_);

      if (list_.empty( ))
         throw "empty!";
      T tmp = list_.front( );
      list_.pop_front( );
      return(tmp);
   }

   T getFront( ) {
      // This is a read-only operation, so you only need a read lock
      boost::read_write_mutex::scoped_read_lock readLock(rwMutex_);
      if (list_.empty( ))
         throw "empty!";
      return(list_.front( ));
   }

private:
   std::list<T> list_;
   boost::read_write_mutex rwMutex_;
};

Queue<std::string> queueOfStrings;

void sendSomething( ) {
   std::string s;

   for (int i = 0; i < 10; ++i) {
      queueOfStrings.enqueue("Cyrus");
   }
}

void checkTheFront( ) {
   std::string s;

   for (int i = 0; i < 10; ++i) {
      try {s = queueOfStrings.getFront( );}
      catch(...) {}
   }
}

int main( ) {

   boost::thread thr1(sendSomething);
   boost::thread_group grp;

   grp.create_thread(checkTheFront);
   grp.create_thread(checkTheFront);
   grp.create_thread(checkTheFront);
   grp.create_thread(checkTheFront);

   thr1.join( );
   grp.join_all( );
}