Some lock doubts

[Marcio Aun Migueis]

Hi ,

I�m using the following map to manage my locked records

  public static Map<Long,Long> lockedRecords = new HashMap<Long,Long>(); 
  

The key value is the record number, and the contents is the cookie. Is this approach correct ? May I use the Java 5 generics to define my map ?

My lock method is

  public long lockRecord(long recNo) throws RecordNotFoundException {
long thisCookie = ++cookie;
if (!existRecordNumber(recNo)){
throw new RecordNotFoundException();
}
//TODO Do I have to synchronize the map ?
while (lockedRecords.containsKey(recNo) && isLockedByAnotherClient(recNo,thisCookie)){
try {
wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
lockedRecords.put(recNo,cookie);
return cookie;
}

Supose we have two clients trying to lock the same record. Before the put command, Client A put his cookie in the map. After that, client B put his own cookie. How to avoid this situation ? Do we have to synchronize the whole method ? Inserting synchronized to my method signature, Am I changing my interface specifications ?

Thanks in advance,

M�rcio
[ September 24, 2005: Message edited by: Marcio Aun Migueis ]

[Andrew Monkhouse]

Hi M�rcio,

May I use the Java 5 generics to define my map ?

Yes, you certainly can, and it is a good idea to do so.

Supose we have two clients trying to lock the same record. Before the put command, Client A put his cookie in the map. After that, client B put his own cookie. How to avoid this situation ? Do we have to synchronize the whole method ? Inserting synchronized to my method signature, Am I changing my interface specifications ?

According to the JLS "an interface may be implemented by a method that is declared strictfp or native or synchronized in a class that implements the interface."

Regards, Andrew

[Marcio Aun Migueis]

Andrew,

Thanks a lot. you really help me.


M�rcio
[ September 26, 2005: Message edited by: Marcio Aun Migueis ]