ACE_Message_Queue高低水位

高水为用来定义消息队列什么时候满：最大盛放的字节数

内部消息队列不可能不受控制一直增大，否则内存爆了也不知道。所以要有水位控制，就行日志文件的循环读写一样。

源代码及其注释说明的很清楚：

  /**   * Get high watermark.   */  virtual size_t high_water_mark (void);  /**   * Set the high watermark, which determines how many bytes can be   * stored in a queue before it's considered "full."   */  virtual void high_water_mark (size_t hwm);  /**   * Get low watermark.   */  virtual size_t low_water_mark (void);  /**   * Set the low watermark, which determines how many bytes must be in   * the queue before supplier threads are allowed to enqueue   * additional ACE_Message_Blocks.   */  virtual void low_water_mark (size_t lwm);

使用示例：

SendToServer consumer(NULL,NULL);ProduceAudio producer(NULL,consumer.msg_queue());producer.msg_queue()->high_water_mark((size_t)(1024*1024*2));