Doctrine_manual-1-2-en

Chapter 10: Component Overview 188
Locking is a mechanism to control concurrency. The two most well known locking strategies
are optimistic and pessimistic locking. The following is a short description of these two
strategies from which only pessimistic locking is currently supported by Doctrine.
Optimistic Locking
The state/version of the object(s) is noted when the transaction begins. When the transaction
finishes the noted state/version of the participating objects is compared to the current state/
version. When the states/versions differ the objects have been modified by another
transaction and the current transaction should fail. This approach is called 'optimistic'
because it is assumed that it is unlikely that several users will participate in transactions on
the same objects at the same time.
Pessimistic Locking
The objects that need to participate in the transaction are locked at the moment the user
starts the transaction. No other user can start a transaction that operates on these objects
while the locks are active. This ensures that the user who starts the transaction can be sure
that no one else modifies the same objects until he has finished his work.
Doctrine's pessimistic offline locking capabilities can be used to control concurrency during
actions or procedures that take several HTTP request and response cycles and/or a lot of time
to complete.
Examples
The following code snippet demonstrates the use of Doctrine's pessimistic offline locking
capabilities.
At the page where the lock is requested get a locking manager instance:
Listing
10-103
// test.php
// ...
$lockingManager = new Doctrine_Locking_Manager_Pessimistic();
Ensure that old locks which timed out are released before we try to acquire our lock 300
seconds = 5 minutes timeout. This can be done by using the releaseAgedLocks()
method.
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10-104
// test.php
// ...
$user = Doctrine_Core::getTable('User')->find(1);
try
{
$lockingManager->releaseAgedLocks(300);
$gotLock = $lockingManager->getLock($user, 'jwage');
if ($gotLock)
{
echo "Got lock!";
}
else
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