Releasing locks

[David Winters Junior]

All,

I have decided to adapt a locking solution as follows:

I have a seperate LockManager class to handle locking records so that only one
client can modify a record at one time.

In my Lock method i use a solution similar to Andrew MonkHouse whereby each client wanting to modiy a record will wait for a specific condition to be triggered.

i include here andrew's code from his book for the reserve lock method

private static Map<String, LockInformation> reservations
 = new HashMap<String, LockInformation>();
 
 private static Lock masterLock = new ReentrantLock();
 
 public boolean reserveDvd(String upc, DvdDatabase renter)
 throws InterruptedException 
{ 
LockInformation dvdLock = null;
masterLock.lock();
 try {
 dvdLock = reservations.get(upc);
 if (dvdLock == null) {
 dvdLock = new LockInformation();
 reservations.put(upc, dvdLock);
 }
 dvdLock.lock();
 } finally {
 masterLock.unlock();
 }
 
 try {
 long endTimeMSec = System.currentTimeMillis() + 5000;
 Condition dvdCondition = dvdLock.getCondition();
 while (dvdLock.isReserved()) {
 long timeLeftMSec = endTimeMSec - System.currentTimeMillis();
 if (!dvdCondition.await(timeLeftMSec, TimeUnit.MILLISECONDS)) {
 return false;
 }
 }
 dvdLock.setReserver(renter);
 } finally {
 
 dvdLock.unlock();
}
 return true;
    

I have completed the following code for the release lock counterpart of this method in the lock manager class and it works okay with the tests i have completed.

I am looking for some feedback here on what one thinks of this code, is their any issues with it as far as one can see:

  void releaseLock(Integer upc, DataAccessImpl renter)throws InterruptedException {
    
      
     
      reservations.get(upc).lock();
     
        if (reservations.get(upc).getReserver().equals(renter)) {
        
        
        LockInformation templock =reservations.get(upc);
        templock.releaseReserver();
        
        reservations.get(upc).getCondition().signalAll();
        
        
        
          }
     
        reservations.get(upc).unlock();
       
       
    }   

Your input would be appreciated

David

[Roman Yankin]

Hi David, honestly this approach is way too complicated, why don't you have just one ReentrantLock and just use lock()/unlock() before/after every operation that requires synchronization?