Multi-Threaded Programming In Java Using Locks Objectives

Multi-Threaded Programming In Java Using Locksobjectivesto Pr

Title: “Multi-threaded Programming in Java Using Locks” Objectives: To practice programming cooperating, synchronized multiple threads of execution. Description: In this programming assignment you will simulate the deposits and withdrawals made to a fictitious bank account. In this case the deposits and withdrawals will be made by synchronized threads. Synchronization is required for two reasons – (1) mutual exclusion (updates cannot be lost) and (2) because a withdrawal cannot occur if the amount of the withdrawal request is greater than the current balance in the account. This means that access to the account (the shared object) must be synchronized.

This application requires cooperation and communication amongst the various threads (cooperating synchronized threads). (In other words, this problem is similar to the producer/consumer problem where there is more than one producer and more than one consumer process active simultaneously.) If a withdrawal thread attempts to withdraw an amount greater than the current balance – then it must block and wait until a deposit has occurred before it can try again. As we covered in the lecture notes, this will require that the deposit threads signal all waiting withdrawal threads whenever a deposit is completed. 1. To keep things relatively simple as well as to see immediate results from a series of transactions (deposits and withdrawals) assume that deposits are made in amounts ranging from $1 to $200 (even dollars only) and withdrawals are made in amounts ranging from $1 to $50 (again, even dollars only).

2. You should have three deposit threads and four withdrawal threads executing simultaneously. 3. Once a deposit thread has executed, put it to sleep for a millisecond or so (depends a little bit on the speed of your system as to how long you will want to sleep the depositor threads - basically we want to ensure a lot more withdrawals than deposits) to allow other threads to execute. This is the only situation in which a deposit thread will block.

4. Once a withdrawal thread has executed, have it yield to another thread (don’t put it to sleep though). This will prevent a single withdrawal thread from gaining the CPU and then executing a long sequence of withdrawal operations. Withdrawal threads block if they attempt to withdraw more than the current balance in the account. 5. Assume all threads have the same priority. 6. The output from your program must look reasonably similar to the sample output shown below. 7. Do not put the threads into a counted loop for your simulation. In other words, the run() method should be an infinite loop. 8. Do not use the Java synchronized statement. I want you to handle the locking and signaling yourself. No monitors!

Paper For Above instruction

The implementation of multi-threaded banking operations in Java, without utilizing the built-in synchronized statement, presents an interesting challenge that demands explicit management of thread cooperation, mutual exclusion, and signaling. This approach essentially involves simulating a bank account where multiple deposit and withdrawal threads operate concurrently, ensuring data integrity and proper synchronization through explicit lock and condition management mechanisms.

In this context, the core problem is handling concurrent deposits and withdrawals in a shared account object, ensuring that withdrawal threads do not withdraw more than the current balance and that no transaction updates are lost. This is akin to the classical producer-consumer problem, where deposit threads act as producers adding funds, and withdrawal threads act as consumers removing funds, with the additional constraint that withdrawals must wait if insufficient funds are available.

Since the assignment explicitly prohibits the use of Java’s synchronized statement and monitors, the implementation relies on explicit locking mechanisms such as java.util.concurrent.locks.Lock and java.util.concurrent.locks.Condition. These classes provide the necessary control over critical sections and thread signaling. By using ReentrantLock, the threads can acquire and release locks explicitly, while conditions facilitate signaling between threads when the account balance changes, allowing waiting withdrawal threads to proceed once deposit threads deposit additional funds.

The main shared resource, the BankAccount class, will include a Lock object and a Condition object. Methods for deposit and withdrawal will acquire the lock explicitly and modify the shared balance. For withdrawals, if the requested amount exceeds the current balance, the thread will wait on the condition variable until signaled by a deposit thread. Similarly, deposit threads will signal all waiting withdrawal threads after completing a deposit to notify them that the balance has increased.

The threads responsible for deposits and withdrawals will run in infinite loops as per the instructions, constantly performing transactions with sleep and yield calls to simulate real-time concurrent activity and enforce fairness. Deposit threads will sleep for approximately a millisecond after each deposit, creating a scenario where there are more withdrawals than deposits over time. Withdrawal threads will yield control after each operation, giving an opportunity for other threads to execute and preventing starvation.

Throughout the implementation, care must be taken to ensure thread safety and proper signaling to avoid deadlocks or data races. Proper use of lock, unlock, await, and signalAll methods ensures that threads coordinate their activities correctly. Additionally, the output will display real-time actions — deposits, withdrawals, waiting states, and signals — providing an illustrative view of multithreaded synchronization in action.

In conclusion, this assignment demonstrates mastery over explicit lock management in Java, bypassing the built-in synchronized keyword, and illustrates effective thread cooperation and communication in a concurrent environment. It emphasizes understanding of low-level synchronization primitives, real-time thread signaling, and safe shared resource management—all integral to advanced concurrent programming in Java.

References

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• Oracle. (2023). java.util.concurrent.locks.Lock. https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/concurrent/locks/Lock.html
• Oracle. (2023). java.util.concurrent.locks.ReentrantLock. https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/concurrent/locks/ReentrantLock.html
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• Jenkings, M. (2020). Designing Thread-safe Applications in Java without synchronized. Software Development Journal.