threads question!

[xi brian]

// Locks a record so that it can only be updated or deleted by this client.
// Returned value is a cookie that must be used when the record is unlocked,
// updated, or deleted. If the specified record is already locked by a
// different
// client, the current thread gives up the CPU and consumes no CPU cycles
// until the record is unlocked.

public long lockRecord(long recNo) throws RecordNotFoundException;

// Releases the lock on a record. Cookie must be the cookie
// returned when the record was locked; otherwise throws SecurityException.

public void unlock(long recNo, long cookie) throws SecurityException;

questions.
1.Returned value is a cookie that must be used when the record is unlocked

(does this cookie must be the recNo ?)

2.If the specified record is already locked by a different client, the current thread gives up the CPU and consumes no CPU cycles until the record is unlocked.

(does the above mean that when current client tries to update a record which is updating by another client. the current client does not allow to do so or the current client has to wait until the lock is released.)

[Vinicius Florentino]

1- No. It's better other, like a random, a sequencial...

2- To update the current client need to LOCK first, if other client is updating, the current will wait the lock release to get the rec lock and do something

[xi brian]

"No. It's better other, like a random, a sequencial..."

please give me a little bit more information on this part.

i am really stuck here

[Simon Hogg]

The returned value from lock() should be the cookie that you use for unlock().

For example to update a record you need to do something like this (pseudocode):

long cookie = lock(recordNum)
update(recordNum, updateData, cookie)
unlock(recordNum, cookie)

What Vinicius is saying is that in the lock method you need to create and return a unique (long) value that you use anywhere the cookie is requested.

The cookie can either be from a sequence (e.g. the first call to lock() returns 1, the second returns 2, the third 3, etc.) or a random number and not be related to the record number at all.

[Anne Crace]

This is how I handled the cookie.

  public long createLockCookie(long recordNum) {

long lockCookie = new Random(recordNum).nextLong();

return lockCookie;

}
  

This method is called from inside the lockRecord(long recNo) method. I declare a variable, long lockCookie = createLockCookie(recNo);
Hope this helps. There are lots of ways to deal with the cookie.

[xi brian]

i got the idea
thank you very much for your help