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What is lock in threading?
Holding a lock is how one thread tells other threads: “I’m changing this thing, don’t touch it right now.” Locks have two operations: acquire allows a thread to take ownership of a lock. If a thread tries to acquire a lock currently owned by another thread, it blocks until the other thread releases the lock.
How do thread locks work?
For a thread to work on an object, it must have control over the lock associated with it, it must “hold” the lock. Only one thread can hold a lock at a time. If a thread tries to take a lock that is already held by another thread, then it must wait until the lock is released.
How do I resolve thread contention?
Use I/O completion ports as solution. Lock contention takes place when a thread tries to acquire the lock to an object which is already acquired by other thread*. Until the object is released, the thread is blocked (in other words, it is in the Waiting state).
Which thread should run after lock has been released?
If the thread cannot acquire both locks, it releases the one it acquires. This is when I am stucking. if the thread releases the lock, the other may access to both instance, and the first thread should stop executing right after it releases the lock.
What can I use instead of thread lock?
Superglue and nail polish as threadlocker alternatives are two of the most common, often quoted as effective replacements for dedicated threadlockers. Using these two products can indeed lock a fastener in place in the short term.
What causes thread contention?
From here: A contention occurs when a thread is waiting for a resource that is not readily available; it slows the execution of your code, but can clear up over time.
How does pessimistic locking manage database resource contention?
Pessimistic Locking: The first user, who accesses the data with the purpose of updating it, locks the data until completing the update. This manages resource contention and does not allow parallel execution. Only one user at a time is allowed to execute the entity bean at a single time.
When does account data skew lead to lock contention?
There are Salesforce-specific situations to be aware of that can lead to lock contention and reduced database concurrency: one such situation is referred to as “account data skew.” Account data skew occurs when an Account’s parent object has more than 10,000 child objects.
How to avoid database resource contention in OC4J?
By default, OC4J and the TopLink EJB 3.0 JPA persistence provider and EJB 2.1 persistence manager provide read-committed transaction isolation. To configure the transaction isolation mode, you must customize the TopLink EJB 3.0 JPA persistence provider or EJB 2.1 persistence manager.
How does optimistic locking work in a database?
Optimistic Locking: Multiple users have read access to the data. When a user attempts to make a change, the application checks a version field (also known as a write-lock field) to ensure the data has not changed since the user read the data.