Question

I have a bufferPool which stores a lot of objects. In order to prevent different threads writing the same object and at the same for efficiency I use ReadWriteLock. But I am not too sure about how it works. After I find the object I want to access,

if(perm.equals(Permissions.READ_ONLY)) {                    
  readLock.lock();
} else if(Permissions.READ_WRITE) {                 
  writeLock.lock(); 
}
return the object I want to access

How does the system know which object the program is trying to access and lock it?
Or my syntax here is wrong? Help!!! Thanks

Answer 1

The system doesn’t know what you’re trying to lock. If you want to use lock objects for a series of items, you’ll have to have a lock for each item, or use one lock for the entire object set (which could be a big bottleneck). This is an example where a single lock is used to synchronize access.

// You'll need to create this somewhere else, in your constructor
// or some other routine that gets called once.
ReentrantLock lock = new ReentrantLock(); 


// Then when you want to access:
lock.lock();
try {
 ... // do stuff with the data
}
finally {
  lock.unlock();
}