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Static variables are class variables that means for each class, there will be
only one static variable instance shared by all the instances of that class. It
DOES NOT mean that only one instance can access it at one time. Therefore,
static variables are not directly related to database locking. Meaning, it does
not matter if you are using static variable or not.
To lock, you either synchronize the method that does the update to the database,
or you can simply reply on the native database locking mechanism. All databases
provide such locking mechanism one way or another. If you are using Oracle, for
instance, you can lock the row you are updating by select it for update. Once it
is locked, no other process (thread) can ever make any update or modification to
that row. This way, you don't have to do anything in your Java codes. When the
row is locked by one thread, all other threads will smiply wait until timeout
and report an error.
Charles
"Srini Sathya." <[EMAIL PROTECTED]> on 10/10/2000 12:22:04 PM
To: [EMAIL PROTECTED]
cc: (bcc: Charles Chen/YellowPages)
From: "Srini Sathya." <[EMAIL PROTECTED]>, 10 October 2000, 12:22
p.m.
Re: Synchronize method in the servlet [Scanned by Yellow Pages PostMaster]
would the DB's will not have an internal lock for their operations??. is it
mandatory to make the DB object static for DB operations.
For example in an online reservation system if you have only one ticket left
and 2 users are trying to reserve at the same milliseconds i believe DB will
not entertain both of their request. Am i right??.
Cheers
Srini
-----Original Message-----
From: Raj Kumar Jha [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, October 10, 2000 11:33 AM
To: [EMAIL PROTECTED]
Subject: Re: Synchronize method in the servlet
It works even if my method is non-static but the database object has to be
static.
Regards,
Raj
----- Original Message -----
From: Peter Pilgrim
To: [EMAIL PROTECTED]
Sent: Tuesday, October 10, 2000 4:02 PM
Subject: Re: Synchronize method in the servlet
Yes my mistake the `databaseLock' has to be static because the method
is static method and cannot there access a non-static individual attribute.
--
Peter Pilgrim
Welcome to the "Me Too" generation.
---------------------------------------- Message
History ----------------------------------------
From: [EMAIL PROTECTED] on 10/10/2000 08:29
Please respond to [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
cc:
Subject: Re: Synchronize method in the servlet
Hi,
I tried this but it doesnt work if I dont declare the databaseLock as
static. Do I need to declare it as static ?
BTW: The databaseLock is just an example of code. You might have
another a class and a method that provides the lock for you as
a single point of accessing the database.
synchronized ( DBPool.getDatabaseLock() ) {
..
}
PS: Most database will provide locking of tables implicity,
integrity of information, otherwise it is __not__ a DB. So
the above in general is not required.
Thanx and Regards,
Raj
----- Original Message -----
From: Peter Pilgrim
To: [EMAIL PROTECTED]
Sent: Friday, October 06, 2000 3:56 PM
Subject: Re: Synchronize method in the servlet
You said that you ONLY want one thread ever accessing/updating the
DB at any one time. So why I have a custom `Object' that locks your
database.
class DBMethoden {
protected Object databaseLock = new Object();
...
void doFunkyPigeon() throws SQLException
{
synchronized ( databaseLock ) {
DBPool pool = DBPool.getInstance();
Connection conx = pool.acquire();
try {
funkyPigeon101( conx );
}
finally {
pool.release( conx );
}
}
}
}
--
Peter Pilgrim
Welcome to the "Me Too" generation.
---------------------------------------- Message
History ----------------------------------------
From: [EMAIL PROTECTED] on 05/10/2000 15:44
Please respond to [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
cc:
Subject: Re: Synchronize method in the servlet
The reason I think I have to put static keyword for the method is because my
method is going to update the database by JDBC connection. I don't want
multiple
thread updating the database at the same time.
Here is my code:
public static synchronized String assignNum(String name, String uID, String
requestType, String comment){
String rID = "";
try{
rID = db.DBinsert(name, uID, requestType, comment);
db.updateSeqNum(requestType);
} catch (Exception e) {
System.err.println(e.toString());
}
return rID;
}
Thanks for the replys.
Tiana
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