hbase之htable线程安全性 HTablePool

在单线程环境下使用hbase的htable是没有问题，但是突然高并发多线程情况下就出现问题了，然后细看htable的api说明

Java代码

* This class is not thread safe for updates; the underlying write buffer can 
 * be corrupted if multiple threads contend over a single HTable instance.  

好吧 ，还是使用前没有细看api的文档说明，而且测试也没有测试多线程使用的情况，检讨下，那么对应的解决方案呢？

当然hbase肯定有自己的解决方案，那就是HTablePool，我们这下仔细看看api文档说明

/**
*AsimplepoolofHTableinstances.
*
*EachHTablePoolactsasapoolforalltables.Touse,instantiatean
*HTablePoolanduse{@link#getTable(String)}togetanHTablefromthepool.
*Onceyouaredonewithit,returnittothepoolwith{@link#putTable(HTableInterface)}.
*
*ApoolcanbecreatedwithamaxSizewhichdefinesthemostHTable
*referencesthatwilleverberetainedforeachtable.Otherwisethedefault
*is{@linkInteger#MAX_VALUE}.
*
*Poolwillmanageitsownclustertothecluster.See{@linkHConnectionManager}.
*/

文档里说，使用getTable来取，当使用完了要用putTable归还，ok，这就是要使用finally块了。

大概的代码结构如下：

    /** 
     * A simple pool of HTable instances.
 
     * 
     * Each HTablePool acts as a pool for all tables.  To use, instantiate an 
     * HTablePool and use {@link #getTable(String)} to get an HTable from the pool. 
     * Once you are done with it, return it to the pool with {@link #putTable(HTableInterface)}. 
     *  
     * 
A pool can be created with a maxSize which defines the most HTable 
     * references that will ever be retained for each table.  Otherwise the default 
     * is {@link Integer#MAX_VALUE}. 
     * 
     * 
Pool will manage its own cluster to the cluster. See {@link HConnectionManager}. 
     */  

Java代码

Result result = null;  
HTable table = null;  
try {  
    table =  (HTable)hbaseTablePool.getTable(tablename);  
    if(table == null) throw new RuntimeException(TABLE_NOT_EXIST);  
    result = table.get(xxxxxx);  
} catch (IOException e) {  
    throw new RuntimeException(e);  
}finally {  
    if(table != null) {  
        hbaseTablePool.putTable((HTableInterface)htable);  
    }  
}

那pool是如何实例化的呢

Java代码

HTablePool  hbaseTablePool = new HTablePool(hbaseStoreFactory.getConfiguration(),this.maxConnection);  
  
//为了检验table的正确性，调用一次      
hbaseTablePool.putTable(this.hbaseTablePool.getTable(tablename));    

仔细看看HTablePool的实现，其实不是pool的概念，只是一个计数器实现而已，相比java的线程池的实现真是很丑陋，希望hbase能给一个比较好的实现了。