Custom Thread Pool

A custom thread pool implementation in Java, built from scratch to explore and understand the internal workings of thread pools. This project focuses on implementing the core mechanisms manually, rather than relying on Java’s built-in concurrency utilities.

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Features

• Custom TaskQueue – A thread-safe FIFO queue implemented from scratch using synchronized, wait(), and notifyAll().
• WorkerThread Management – Multiple worker threads continuously dequeue and execute tasks.
• Graceful Shutdown – Supports a clean shutdown where queued tasks are completed using the poison pill pattern.
• Immediate Shutdown – Can stop all active tasks and return unexecuted tasks immediately.
• Rejection Policies – Handles tasks submitted after shutdown with configurable strategies:
  • ABORT_POLICY – Throws a RuntimeException.
  • DISCARD_POLICY – Silently discards the task.
  • CALLER_RUNS_POLICY – Runs the task in the calling thread.
  • DISCARD_OLDEST_POLICY – Removes the oldest queued task to make room for the new task.
• Exception Handling – Worker threads catch exceptions from tasks to prevent thread death.
• Custom Thread Factory – Allows naming threads and configuring priorities.

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Project Structure

custom-thread-pool/
├─ pom.xml
├─ README.md
├─ src/
│ ├─ main/java/com/brendanddev/threadpool/
│ │ ├─ CustomThreadPool.java
│ │ ├─ TaskQueue.java
│ │ ├─ WorkerThread.java
│ │ ├─ CustomThreadFactory.java
│ │ ├─ Main.java
│ │ └─ policies/
│ │ ├─ RejectionHandler.java
│ │ └─ RejectionHandlers.java
├─ target/...

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Usage

1. Compile and run:

mvn clean compile exec:java

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References & Inspiration

• Java Concurrency Tutorial
• Baeldung: Building Thread Pools
• Poison Pill Pattern
• Thread Pool Policies
• Java Thread Pool Execution and Rejection Policies