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社区首页 >专栏 >GenericObjectPool参数解析

GenericObjectPool参数解析

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code4it
发布2018-09-17 15:09:46
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发布2018-09-17 15:09:46
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文章被收录于专栏:码匠的流水账

本文主要解析一下apache common pools下的GenericObjectPool的参数设置

GenericObjectPool

commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPool.java

代码语言:javascript
复制
public class GenericObjectPool<T> extends BaseGenericObjectPool<T>
        implements ObjectPool<T>, GenericObjectPoolMXBean, UsageTracking<T> {
   //......
}

默认配置见 commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPoolConfig.java

代码语言:javascript
复制
public class GenericObjectPoolConfig extends BaseObjectPoolConfig {

    /**
     * The default value for the {@code maxTotal} configuration attribute.
     * @see GenericObjectPool#getMaxTotal()
     */
    public static final int DEFAULT_MAX_TOTAL = 8;

    /**
     * The default value for the {@code maxIdle} configuration attribute.
     * @see GenericObjectPool#getMaxIdle()
     */
    public static final int DEFAULT_MAX_IDLE = 8;

    /**
     * The default value for the {@code minIdle} configuration attribute.
     * @see GenericObjectPool#getMinIdle()
     */
    public static final int DEFAULT_MIN_IDLE = 0;

    private int maxTotal = DEFAULT_MAX_TOTAL;

    private int maxIdle = DEFAULT_MAX_IDLE;

    private int minIdle = DEFAULT_MIN_IDLE;

    //......
}

pool基本参数

基本参数

  • lifo GenericObjectPool 提供了后进先出(LIFO)与先进先出(FIFO)两种行为模式的池。默认为true,即当池中有空闲可用的对象时,调用borrowObject方法会返回最近(后进)的实例
  • fairness 当从池中获取资源或者将资源还回池中时 是否使用java.util.concurrent.locks.ReentrantLock.ReentrantLock 的公平锁机制,默认为false

数量控制参数

  • maxTotal 链接池中最大连接数,默认为8
  • maxIdle 链接池中最大空闲的连接数,默认也为8
  • minIdle 连接池中最少空闲的连接数,默认为0

超时参数

  • maxWaitMillis 当连接池资源耗尽时,等待时间,超出则抛异常,默认为-1即永不超时
  • blockWhenExhausted 当这个值为true的时候,maxWaitMillis参数才能生效。为false的时候,当连接池没资源,则立马抛异常。默认为true

test参数

  • testOnCreate 默认false,create的时候检测是有有效,如果无效则从连接池中移除,并尝试获取继续获取
  • testOnBorrow 默认false,borrow的时候检测是有有效,如果无效则从连接池中移除,并尝试获取继续获取
  • testOnReturn 默认false,return的时候检测是有有效,如果无效则从连接池中移除,并尝试获取继续获取
  • testWhileIdle 默认false

检测参数

  • timeBetweenEvictionRunsMillis 空闲链接检测线程检测的周期,毫秒数。如果为负值,表示不运行检测线程。默认为-1.

commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/GenericObjectPool.java

代码语言:javascript
复制
public GenericObjectPool(PooledObjectFactory<T> factory,
            GenericObjectPoolConfig config) {

        super(config, ONAME_BASE, config.getJmxNamePrefix());

        if (factory == null) {
            jmxUnregister(); // tidy up
            throw new IllegalArgumentException("factory may not be null");
        }
        this.factory = factory;

        idleObjects = new LinkedBlockingDeque<PooledObject<T>>(config.getFairness());

        setConfig(config);

        startEvictor(getTimeBetweenEvictionRunsMillis());
    }

commons-pool2-2.4.2-sources.jar!/org/apache/commons/pool2/impl/BaseGenericObjectPool.java

代码语言:javascript
复制
/**
     * The idle object evictor {@link TimerTask}.
     *
     * @see GenericKeyedObjectPool#setTimeBetweenEvictionRunsMillis
     */
    class Evictor extends TimerTask {
        /**
         * Run pool maintenance.  Evict objects qualifying for eviction and then
         * ensure that the minimum number of idle instances are available.
         * Since the Timer that invokes Evictors is shared for all Pools but
         * pools may exist in different class loaders, the Evictor ensures that
         * any actions taken are under the class loader of the factory
         * associated with the pool.
         */
        @Override
        public void run() {
            ClassLoader savedClassLoader =
                    Thread.currentThread().getContextClassLoader();
            try {
                if (factoryClassLoader != null) {
                    // Set the class loader for the factory
                    ClassLoader cl = factoryClassLoader.get();
                    if (cl == null) {
                        // The pool has been dereferenced and the class loader
                        // GC'd. Cancel this timer so the pool can be GC'd as
                        // well.
                        cancel();
                        return;
                    }
                    Thread.currentThread().setContextClassLoader(cl);
                }

                // Evict from the pool
                try {
                    evict();
                } catch(Exception e) {
                    swallowException(e);
                } catch(OutOfMemoryError oome) {
                    // Log problem but give evictor thread a chance to continue
                    // in case error is recoverable
                    oome.printStackTrace(System.err);
                }
                // Re-create idle instances.
                try {
                    ensureMinIdle();
                } catch (Exception e) {
                    swallowException(e);
                }
            } finally {
                // Restore the previous CCL
                Thread.currentThread().setContextClassLoader(savedClassLoader);
            }
        }
    }
  • numTestsPerEvictionRun 在每次空闲连接回收器线程(如果有)运行时检查的连接数量,默认为3 private int getNumTests() { int numTestsPerEvictionRun = getNumTestsPerEvictionRun(); if (numTestsPerEvictionRun >= 0) { return Math.min(numTestsPerEvictionRun, idleObjects.size()); } else { return (int) (Math.ceil(idleObjects.size() / Math.abs((double) numTestsPerEvictionRun))); } }
  • minEvictableIdleTimeMillis 连接空闲的最小时间,达到此值后空闲连接将可能会被移除。默认为1000L 60L30L
  • softMinEvictableIdleTimeMillis 连接空闲的最小时间,达到此值后空闲链接将会被移除,且保留minIdle个空闲连接数。默认为-1.
  • evictionPolicyClassName evict策略的类名,默认为org.apache.commons.pool2.impl.DefaultEvictionPolicy public class DefaultEvictionPolicy<T> implements EvictionPolicy<T> { @Override public boolean evict(EvictionConfig config, PooledObject<T> underTest, int idleCount) { if ((config.getIdleSoftEvictTime() < underTest.getIdleTimeMillis() && config.getMinIdle() < idleCount) || config.getIdleEvictTime() < underTest.getIdleTimeMillis()) { return true; } return false; } } 这里就用到了上面提到的两个参数

doc

  • Apache commons-pool对象池原理分析
  • GenericObjectPool 避免泄漏
  • apache-common-pool2(配置参数详解,以及资源回收,从池中获取资源,将资源返还给池 逻辑解析)
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目录
  • GenericObjectPool
  • pool基本参数
    • 基本参数
      • 数量控制参数
        • 超时参数
          • test参数
            • 检测参数
            • doc
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