How to Ensure Java Utilizes All Available CPUs on Your Machine

Why does Java not utilize all available CPUs on my machine?

When running Java applications, sometimes the JVM (Java Virtual Machine) does not utilize all the available CPU cores on your machine, which can lead to underperformance. This issue often arises due to default JVM configurations, thread limitations, or specific application code. Below we will explore the reasons and the steps you can take to improve CPU utilization.

ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());

executor.submit(() -> { 
    // Task to execute 
}); 

executor.shutdown(); // Don't forget to shutdown the executor cleanly.

Causes

• The Java Virtual Machine (JVM) may not be configured to utilize multiple threads efficiently.
• The application code may have synchronization issues that limit concurrency.
• Default garbage collection settings can introduce pauses, effectively blocking CPU usage during critical operations.
• Single-threaded tasks that do not leverage parallel processing.

Solutions

• Use the `-XX:ParallelGCThreads=n` JVM option to specify the number of garbage collection threads, where 'n' is equal to the number of available CPU cores.
• Implement multithreading in your application by using Executors or Thread classes to leverage multiple cores effectively.
• Analyze and optimize your code to reduce bottlenecks caused by synchronized methods or locks.
• Profile your application and monitor CPU usage to identify hotspots that require optimization.

Mistake: Not configuring the JVM parameters for thread management.

Solution: Always review and, if necessary, adjust JVM settings like `-Xms`, `-Xmx`, and `-XX:ParallelGCThreads`.

Mistake: Assuming that adding more threads will always increase performance.

Solution: Monitor thread contention and only increase thread count when there's a logical benefit, considering the application's workload.