Question

I have a class named “Channel” with two methods defined:

class Channel {

    void read(){...}
    void write(){...}
}

There’s an instance of this class used in multi-threaded environment. Several threads periodically read from channel while one thread periodically writes to it. Read operation is thread-safe so that it is ok for several reads to occur simultaneously. However once write operation starts, read threads must be blocked until write operation is finished. It is essential to keep read operations as fast as possible and avoid resource-consuming synchronization routines.

What would be the most appropriate pattern to implement such behaviour? Maybe java classes or libraries to help?

Answer 1

Use a ReadWriteLock. It will allow concurrent reads to occur with serial writes. To further satisfy your requirements, an acquisition of a writeLock will prevent any readLock‘s from making progress until a subsequent release.

class Channel {
    final ReadWriteLock lock = new ReentrantReadWriteLock();

    void read(){
      lock.readLock().lock();
      try{

      }finally{
         lock.readLock().unlock();
      }
    }
    void write(){   
      lock.writeLock().lock();
      try{

      }finally{
         lock.writeLock().unlock();
      }
    }
}