For this Project 3 Threads milestone, your project must maintain the functionality from the Project 2 Search assignment using a custom-made conditional read/write lock to create a thread-safe inverted index and a custom-made work queue to manage worker threads.

To do this, you should either create new classes or extend existing classes to support multithreading. DO NOT REMOVE YOUR SINGLE THREADING CODE, as you still need to support single threaded building and searching the index.

<aside> <img src="/icons/error_gray.svg" alt="/icons/error_gray.svg" width="40px" /> Do NOT use any of the classes in the java.util.concurrent package and do NOT use the Stream.parallel method for the multithreaded code.

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TABLE OF CONTENTS

Prerequisites

You must complete the following assignments before beginning to work on this one:

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Functionality

Your main method must be placed in a class named Driver and must process the following additional command-line arguments:

• -threads [num] where the flag -threads indicates your code must initialize a thread-safe inverted index, work queue, and enable multithreaded search. See the “Multithreaded Search” section for details.

  The next optional argument [num] is the number of worker threads to use in a work queue. If the [num] argument is not provided, not a number, or less than 1, use 5 as the default number of worker threads.

  For all v3.0 releases of this project, only multithread the search process. Do not multithread the build process.

These are in addition to the command-line arguments from the previous Project 2 Search assignment.

The command-line flag/value pairs may be provided in any order or not at all. Do not convert paths to absolute form when processing command-line input!

Output user-friendly error messages in the case of exceptions or invalid input. Under no circumstance should your main() method output a stack trace to the user!

<aside> <img src="/icons/warning_gray.svg" alt="/icons/warning_gray.svg" width="40px" /> If the -threads flag is not provided, then multithreading should not be enabled. A thread-safe inverted index should not be initialized, a work queue should not be initialized, and no worker threads should be created. Your main method should behave the same as previous projects.

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Multithreaded Search

If multithreading is enabled, the search process from Project v2.1 Tests must be multithreaded as follows:

• A custom-made conditional read/write lock must be used to make the inverted index thread-safe. This conditional lock must support concurrent read operations, non-concurrent write and mixed read/write operations, and allow an active writer to acquire additional read or write locks as necessary (i.e. a reentrant write lock). See the MultiReaderLock homework for how to create this conditional read/write lock.
• A custom-made thread pool and work queue must be used to manage all worker threads. The work queue must support the ability to automatically track pending (or unfinished) work (or tasks), and provide a method that waits until there is no more pending work. The work queue should also support the ability to shutdown gracefully, and should be gracefully shutdown before the main method exits. See the PrimeFinder homework for how to create this work queue.