Acquire an EXCLUSIVE lock on DB

Question

Background

I am updating a DB From a Service at a certain time daily, while this DB is under update and the user tries to open the app I want to hold on and dont display what is going on, though my service is a typical Cron job implemented in the background. What can be done to achieve this? Also I want to acquire a lock on the DB so that the records dont get messed up. Would appreciate any tuts or any related algos in this regard.

Answer 1

Here is how you can lock your database using a ReentrantReadWriteLock .

// Create the lock object
private ReentrantReadWriteLock lockSqliteDB = new ReentrantReadWriteLock();

// Called to update the database
public void updateDatabase() {
    try {
        lockSqliteDB.writeLock().lock();

        // Read and update the database here

    } finally {
        sqliteDB.close();
        lockSqliteDB.writeLock().unlock();
    }
}

// Called to read from the database
public void readDatabase() {
    try {
        lockSqliteDB.readLock().lock();

        // Read from the database here

    } finally {
        sqliteDB.close();
        lockSqliteDB.readLock().unlock();
    }
}

Note that multiple threads will be able to read from the database simultaneously with the read lock. However, a single thread can be writing to the database with the write lock, during which no other threads will be able to read or write.