前提

Tomcat 10.1.x

Tomcat线程池介绍

Tomcat线程池，源于JAVA JDK自带线程池。由于JAVA JDK线程池策略，比较适合处理 CPU 密集型任务，但是对于 I/O 密集型任务，如数据库查询，rpc 请求调用等，不是很友好，所以Tomcat在其基础上进行了扩展。

任务处理流程

扩展线程池相关源码简析

Tomcat中定义了一个StandardThreadExecutor类，该类实现了org.apache.catalina.Executor，org.apache.tomcat.util.threads.ResizableExecutor接口

该类内部定义了namePrefix(创建的线程名称前缀，默认值tomcat-exec-)，maxThreads(最大线程数，默认值 200)，minSpareThreads(最小线程数，即核心线程数，默认值 25)，maxIdleTime（线程最大空闲时间，毫秒为单位，默认值60秒），maxQueueSize(最大队列大小，默认值 Integer.MAX_VALUE)等属性，此外，还定义了一个org.apache.tomcat.util.threads.ThreadPoolExecutor类型的执行器对象，一个execute(Runnable command) 方法

当execute(Runnable command) 方法被调用时，会调用上述ThreadPoolExecutor类对象的execute方法

org.apache.catalina.core.StandardThreadExecutor.java

import org.apache.catalina.Executor;
import org.apache.catalina.LifecycleException;
import org.apache.catalina.LifecycleState;
import org.apache.catalina.util.LifecycleMBeanBase;
import org.apache.tomcat.util.res.StringManager;
import org.apache.tomcat.util.threads.ResizableExecutor;
import org.apache.tomcat.util.threads.TaskQueue;
import org.apache.tomcat.util.threads.TaskThreadFactory;
import org.apache.tomcat.util.threads.ThreadPoolExecutor;

public class StandardThreadExecutor extends LifecycleMBeanBase
        implements Executor, ResizableExecutor {

    protected static final StringManager sm = StringManager.getManager(StandardThreadExecutor.class);

    // ---------------------------------------------- Properties
    /**
     * Default thread priority
     */
    protected int threadPriority = Thread.NORM_PRIORITY;

    /**
     * Run threads in daemon or non-daemon state
     */
    protected boolean daemon = true;

    /**
     * Default name prefix for the thread name
     */
    protected String namePrefix = "tomcat-exec-";

    /**
     * max number of threads
     */
    protected int maxThreads = 200;

    /**
     * min number of threads
     */
    protected int minSpareThreads = 25;

    /**
     * idle time in milliseconds
     */
    protected int maxIdleTime = 60000;

    /**
     * The executor we use for this component
     */
    protected ThreadPoolExecutor executor = null;

    /**
     * the name of this thread pool
     */
    protected String name;

    /**
     * The maximum number of elements that can queue up before we reject them
     */
    protected int maxQueueSize = Integer.MAX_VALUE;

    /**
     * After a context is stopped, threads in the pool are renewed. To avoid
     * renewing all threads at the same time, this delay is observed between 2
     * threads being renewed.
     */
    protected long threadRenewalDelay =
        org.apache.tomcat.util.threads.Constants.DEFAULT_THREAD_RENEWAL_DELAY;

    private TaskQueue taskqueue = null;
    // ---------------------------------------------- Constructors
    public StandardThreadExecutor() {
        //empty constructor for the digester
    }
    
    //....此处代码已省略

    @Override
    public void execute(Runnable command) {
        if (executor != null) {
            // Note any RejectedExecutionException due to the use of TaskQueue
            // will be handled by the o.a.t.u.threads.ThreadPoolExecutor
            executor.execute(command);
        } else {
            throw new IllegalStateException(sm.getString("standardThreadExecutor.notStarted"));
        }
    }
    
    //....此处代码已省略

}

当org.apache.tomcat.util.threads.ThreadPoolExecuto类对象的execute(Runnable command) 方法被调用时，会调用该类定义的一个executeInternal方法，并在捕获到RejectedExecutionException异常时，尝试再次将任务放入工作队列中。

executeInternal方法中，通过代码可知，