ReadWriteLock

For this homework, you will create a conditional read write lock and a thread safe indexed set using that lock.

Hints

Below are some hints that may help with this homework assignment:

• There are some differences between the IndexedSet version presented in lecture and the one provided here. You will have to determine if those differences change which methods should or shouldn't be overridden!

• Start with using built-in options to make the ThreadSafeIndexedSet thread safe, instead of your own custom SimpleReadWriteLock class. This should help you pass the non-approach tests in ThreadSafeIndexedSetTest to make sure you are @Overriding methods correctly. Specifically:

  • Use the synchronized keyword and @Override the appropriate methods. Try to pass the ThreadSafeIndexedSetTest tests that check your code is overriding the correct methods (the testOverridden and testNotOverridden test methods).

  • Switch to using the built-in ReentrantReadWriteLock to make those methods thread-safe instead. Try to pass the other non-approach ThreadSafeIndexedSetTest tests. When using the conditional lock, decide whether a block of operations are read operations, write operations, or mixed read and write operations with respect to the shared data. Look at the lecture notes for discussion and code on conditional locks and how they can be used.

  • Finally, switch to using the SimpleReadWriteLock class and switch your focus on passing the SimpleReadWriteLock tests next. The ReentrantReadWriteLock and SimpleReadWriteLock classes are designed to be interchangeable, so you should be able to swap without modifying most of your code.

• The Javadoc comments for the SimpleReadWriteLock are written to give clues on the conditions the code should use for the wait() or notifyAll() calls.

• The lecture notes discuss a simple read write lock, but the one you must create is more complicated. In addition to tracking the number of readers and writers, it must track the active writer as well.

  This includes setting the active writer when a thread acquires the write lock and unsetting the active writer when the lock is fully released. The active writer can acquire additional read or write locks as long as it is the active writer.

  Leave this part for the end, after you have a simple read write lock already working.

• Passing the provided tests consistently is a good sign, but the tests may not catch all implementation issues. However, any time a test fails indicates there is a multithreading problem somewhere (even if it sometimes passes). Logging can help debug these cases.

These hints are optional. There may be multiple approaches to solving this homework.

Requirements

See the Javadoc and TODO comments in the template code in the src/main/java directory for additional details. You must pass the tests provided in the src/test/java directory. Do not modify any of the files in the src/test directory.

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