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"ScheduledThreadPoolExecutor" Should Not Have 0 Core Threads

High
maintainabilityreliability

What is it?​

This practice is triggered when the corePoolSize of a ScheduledThreadPoolExecutor is set to zero. This can lead to a situation where no tasks are executed as there are no threads available to run the scheduled tasks.

Why apply it?​

Having a corePoolSize of zero means the executor will have no threads allocated to run tasks, potentially leading to unexpected application behavior and failure to execute scheduled operations.

How to fix it?​

Ensure that the corePoolSize is set to a value greater than zero, thus allowing tasks to be scheduled and executed as intended.

Examples​

Example 1:​

Negative​

The negative example improperly sets corePoolSize to zero, preventing tasks from being executed by the ScheduledThreadPoolExecutor.

import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class TaskScheduler {

  public void scheduleTasks() {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(0);  // Noncompliant
    executor.schedule(() -> {
      System.out.println("Task executed");
    }, 1, TimeUnit.SECONDS);
  }
}

Example 2:​

Positive​

The positive example correctly sets the corePoolSize of the ScheduledThreadPoolExecutor to a value greater than zero, ensuring tasks can be run.

import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class TaskScheduler {

  public void scheduleTasks() {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(5);  // Compliant
    executor.schedule(() -> {
      System.out.println("Task executed");
    }, 1, TimeUnit.SECONDS);
  }
}

Negative​

The negative example incorrectly sets the corePoolSize to zero using the setCorePoolSize method, leading to no threads available for task execution.

import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class PeriodicScheduler {

  public void initiateScheduler() {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(2);
    executor.setCorePoolSize(0);  // Noncompliant
    executor.scheduleWithFixedDelay(() -> {
      System.out.println("Executing periodic task");
    }, 0, 5, TimeUnit.SECONDS);
  }
}

Example 3:​

Positive​

The positive example correctly configures the corePoolSize using the setCorePoolSize method to a value greater than zero.

import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class PeriodicScheduler {

  public void initiateScheduler() {
    ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(2);
    executor.setCorePoolSize(5);  // Compliant
    executor.scheduleWithFixedDelay(() -> {
      System.out.println("Executing periodic task");
    }, 0, 5, TimeUnit.SECONDS);
  }
}