Java Thread Pools - Unbounded Queue Exhausts Heap

package io.thecodeforge.concurrency;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * io.thecodeforge production example: Managed Task Execution
 */
public class ForgeTaskProcessor {
    public void processBatch() {
        // io.thecodeforge: Using a fixed pool to prevent thread explosion
        ExecutorService executor = Executors.newFixedThreadPool(4);

        for (int i = 0; i < 10; i++) {
            final int taskId = i;
            executor.submit(() -> {
                String threadName = Thread.currentThread().getName();
                System.out.println("Forge Worker [" + threadName + "] processing task: " + taskId);
                try { 
                    TimeUnit.MILLISECONDS.sleep(500); 
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            });
        }

        // Graceful shutdown is non-negotiable for production code
        executor.shutdown();
        try {
            if (!executor.awaitTermination(60, TimeUnit.SECONDS)) {
                executor.shutdownNow();
            }
        } catch (InterruptedException e) {
            executor.shutdownNow();
        }
    }
}

package io.thecodeforge.concurrency.config;

import java.util.concurrent.*;

public class SafeExecutorConfig {
    /**
     * io.thecodeforge: Best practice - Manual configuration for production.
     * Prevents OutOfMemoryErrors by bounding the task queue.
     */
    public static ExecutorService createProductionPool() {
        return new ThreadPoolExecutor(
            10,                      // corePoolSize: Threads kept alive
            25,                      // maximumPoolSize: Max threads allowed
            60L, TimeUnit.SECONDS,   // keepAliveTime: Idle thread expiration
            new LinkedBlockingQueue<>(500), // Bounded queue: Capacity limit
            new ThreadPoolExecutor.CallerRunsPolicy() // Saturation policy: Throttles producer
        );
    }
}

package io.thecodeforge.concurrency.config;

import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Custom ThreadPoolExecutor with monitoring hooks.
 */
public class CustomThreadPoolExecutor extends ThreadPoolExecutor {
    private final AtomicInteger submittedTasks = new AtomicInteger();
    private final AtomicInteger completedTasks = new AtomicInteger();

    public CustomThreadPoolExecutor(int corePoolSize, int maximumPoolSize,
                                     long keepAliveTime, TimeUnit unit,
                                     BlockingQueue<Runnable> workQueue,
                                     RejectedExecutionHandler handler) {
        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);
    }

    @Override
    public void execute(Runnable command) {
        submittedTasks.incrementAndGet();
        super.execute(command);
    }

    @Override
    protected void afterExecute(Runnable r, Throwable t) {
        completedTasks.incrementAndGet();
        // Log unreported exceptions
        if (t != null) {
            System.err.println("Uncaught exception in task: " + t.getMessage());
        }
        super.afterExecute(r, t);
    }

    public int getSubmittedCount() { return submittedTasks.get(); }
    public int getCompletedCount() { return completedTasks.get(); }
}

package io.thecodeforge.concurrency.config;

import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

public class NamedThreadFactory implements ThreadFactory {
    private final String namePrefix;
    private final AtomicInteger threadNumber = new AtomicInteger(1);
    private final boolean daemon;

    public NamedThreadFactory(String poolName, boolean daemon) {
        this.namePrefix = poolName + "-";
        this.daemon = daemon;
    }

    @Override
    public Thread newThread(Runnable r) {
        Thread t = new Thread(r, namePrefix + threadNumber.getAndIncrement());
        t.setDaemon(daemon);
        t.setUncaughtExceptionHandler((thread, throwable) -> 
            System.err.println("Uncaught in " + thread.getName() + ": " + throwable.getMessage()));
        return t;
    }
}

// Usage:
// ExecutorService pool = new ThreadPoolExecutor(..., new NamedThreadFactory("order-processing", false));

package io.thecodeforge.concurrency.config;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class GracefulShutdownWrapper {
    private static final Logger LOG = Logger.getLogger(GracefulShutdownWrapper.class.getName());

    public static void shutdownAndAwaitTermination(ExecutorService pool, long timeout, TimeUnit unit) {
        pool.shutdown(); // Disable new tasks
        try {
            // Wait a while for existing tasks to terminate
            if (!pool.awaitTermination(timeout, unit)) {
                LOG.warning("Pool did not terminate within timeout. Forcing shutdown.");
                pool.shutdownNow(); // Cancel currently executing tasks
                // Wait again for tasks to respond to interruption
                if (!pool.awaitTermination(30, TimeUnit.SECONDS)) {
                    LOG.severe("Pool did not terminate even after force shutdown.");
                }
            }
        } catch (InterruptedException ie) {
            // (Re-)Cancel if current thread also interrupted
            pool.shutdownNow();
            // Preserve interrupt status
            Thread.currentThread().interrupt();
        }
    }
}

package io.thecodeforge.concurrency.monitoring;

import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.atomic.AtomicLong;

public class ThreadPoolMonitor {
    private final ThreadPoolExecutor executor;
    private final AtomicLong lastRejectedCount = new AtomicLong(0);

    public ThreadPoolMonitor(ThreadPoolExecutor executor) {
        this.executor = executor;
    }

    public void logMetrics() {
        long active = executor.getActiveCount();
        long poolSize = executor.getPoolSize();
        long queueSize = executor.getQueue().size();
        long completed = executor.getCompletedTaskCount();
        long rejected = executor.getRejectedExecutionHandler().getClass().getSimpleName().contains("Abort") ? 
                         ? 0 : 0; // In real code, track via custom handler
        System.out.printf("Pool: %s, Active: %d, Size: %d, Queue: %d, Completed: %d%n",
            executor.toString(), active, poolSize, queueSize, completed);
    }

    public boolean isHealthy(long queueThreshold) {
        return executor.getQueue().size() < queueThreshold && 
               executor.getActiveCount() < executor.getMaximumPoolSize();
    }
}