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improvement for master

At present, the problems of master:

1. There are many polling, that result in unnecessary time-cost

2. The distributed lock is used when the command is taken, that result in the bottleneck of concurrency

3. Too many threads(nProcessInstance*nTaskInstances) are used, that result in the waste of system resources

4. Polling database result in database query pressure bottleneck

Master模块优化：
目前的master：

目前发现master的问题：

1. 出现比较多的轮询，造成不必要的耗时
2. 取command的时候使用了分布式锁，造成并发数量的瓶颈
3. 线程使用过多(nProcessInstance*nTaskInstances) ，造成系统资源浪费的现象
4. 轮询数据库，数据量大的情况下，造成数据库查询压力瓶颈