Using @Transactional for thread safety

Question

My question is, as soon as the @Transactional annotation controls the execution of code and transactions. To properly install the Spring application and the following code:

@Transactional public void withdraw(int amount) { if(isEnoughFunds(amount)) { decreaseFunds(amount); } } 

Is the following scenario possible?

• funds == 100; quantity == 100
• thread A enters output / transaction A starts
• thread A executes isEnoughFunds, which evaluates to true
• thread B enters shutdown / transaction B starts
• thread B executes isEnoughFunds, which evaluates to true
• thread A performs a reduction Funds / thread A blocks a db write
• thread B waits for thread A to commit the transaction and lock the write lock.
• thread A completes the output / transaction A completes
• thread B performs a reduction Funds / thread B blocks writing db
• thread B completes the output / transaction B commits
• funds == -100

If possible, how would you prevent this?

Answer 1

Yes, it is possible, depending on the level of insulation. To prevent this, you can explicitly get a read lock from the database before calling ifEnoughFunds (). The lock will be released at the end of the transaction. In this case, thread B will always wait for the transaction of thread A to commit.