在if语句外定义了ed，赋值为m_eventInputManager->getById(ticket)的返回值，如果未找到对应的Event Descriptor,
则返回EventInputManager::EIM_MAYCOME或者EventInputManager::EIM_NEVERTOCOME。

在if语句内也定义了ed, 赋值为m_eventInputManager->getEventDescriptor(mem_page)返回值，这是根据造的空数据的
内存内存地址得到对应的event descriptor，并修改该ED的值为ticket，然后根据ticket将该ed放进对应的List。

但是if语句里有对丢失数据的状态判断，这应该是用到的if外的ed值。在if语句重新定义ed后，覆盖了该if外的ed值，？？？此处是
不是有bug?



178 /**************************************************************/
179 ROS::EventFragment* PCMemoryDataChannel::getFragment(int ticket)
180 /**************************************************************/
181 {
182   evDesc_t *ed;
183   MemoryPage *mem_page;
184   EventFragment *fragment=0;
185 
186   DEBUG_TEXT(DFDB_ROSFM, 10, "PCMemoryDataChannel::getFragment: fragment with L1ID " << ticket << " requested");
187   // protect EIM and fast allocate with same mutex
188   m_mutex->lock();
189 
190   //Find the requested event
191   ed = m_eventInputManager->getById(ticket);
192 
193   if (m_fragType == 0)
194   {
195     DEBUG_TEXT(DFDB_ROSFM, 10, "PCMemoryDataChannel::getFragment: processing ROB fragment");
196     if((intptr_t)ed == EventInputManager::EIM_MAYCOME || (intptr_t)ed == EventInputManager::EIM_NEVERTOCOME)
197     {
198     DEBUG_TEXT(DFDB_ROSFM, 8, "EIM_MAYCOME || EIM_NEVERTOCOME " << ticket <<  "ed:" << ed <<std::endl);
199     try
200     {
201       fragment = new ROBFragment(m_memoryPool, ticket, m_sourceIdentifier, 0); //create an empty ROB fragment
202       Buffer *mem_buffer = fragment->buffer();                                 //get the Buffer of the ROB fragment
203       Buffer::page_iterator mem_page_i = mem_buffer->begin();
204       MemoryPage *mem_page = const_cast<MemoryPage *>(*mem_page_i);            //get the memory page of the buffer
205       mem_page->lock();
206 
207       evDesc_t *ed = m_eventInputManager->getEventDescriptor(mem_page);        //get a pointer to the event descriptor
208       ed->L1id = ticket;                                                       //set the L1ID
209       m_eventInputManager->createEvent(ed);                                    //Insert the event into the Event Input Manager
210 
211       if ((intptr_t)ed == EventInputManager::EIM_MAYCOME)
212       {
213         m_statistics->fragmentsMissed++;
214         fragment->setStatus(EventFragment::STATUS_MAYCOME);
215         DEBUG_TEXT(DFDB_ROSFM, 8, "PCMemoryDataChannel::getFragment: Fragment for L1ID " << ticket << " has not yet arrived");
216       }
217 
218       if ((intptr_t)ed == EventInputManager::EIM_NEVERTOCOME)
219       {
220         m_statistics->fragmentsLost++;
221         fragment->setStatus(EventFragment::STATUS_LOST);
222         DEBUG_TEXT(DFDB_ROSFM, 8, "PCMemoryDataChannel::getFragment: Fragment for L1ID " << ticket << " does not exist");
223         CREATE_ROS_EXCEPTION(ex1, CoreException, PCMEMCHAN_LOST, "\n L1ID = " << ticket << ", ROL physical addr = " << physicalAddr    ess());
224         ers::warning(ex1);
225       }
226     }
227       catch (EventFragmentException& e)
228       {
229         DEBUG_TEXT(DFDB_ROSFM, 8, "PCMemoryDataChannel::getFragment:EventFragmentException");
230         DEBUG_TEXT(DFDB_ROSFM, 5, e);
231         m_mutex->unlock();
232         throw e;
233       }
234       m_mutex->unlock();
235       return(fragment);
236     }
237   }
238 
239   if (m_fragType == 1)
240   {
241     DEBUG_TEXT(DFDB_ROSFM, 10, "PCMemoryDataChannel::getFragment: processing full fragment");
242     if ((intptr_t)ed == EventInputManager::EIM_MAYCOME || (intptr_t)ed == EventInputManager::EIM_NEVERTOCOME)
243     {
244       DEBUG_TEXT(DFDB_ROSFM, 5, "PCMemoryDataChannel::getFragment: Fragment for L1ID " << ticket << " is not available");
245       CREATE_ROS_EXCEPTION(ex1, CoreException, NODATA, "L1ID = " << ticket << ", ROL physical addr = " << physicalAddress());
246       throw(ex1);
247     }
248   }
249 
250   m_statistics->fragmentsServed++;
251   DEBUG_TEXT(DFDB_ROSFM, 20, "PCMemoryDataChannel::getFragment: getById returns " << HEX(ed));
252   mem_page = ed->myPage;
253 
254   DEBUG_TEXT(DFDB_ROSFM, 20, "PCMemoryDataChannel::getFragment: Dumping fields of this event descriptor:");
255   DEBUG_TEXT(DFDB_ROSFM, 20, "PCMemoryDataChannel::getFragment: Address of memory page = " << std::hex << mem_page << std::dec);
256   DEBUG_TEXT(DFDB_ROSFM, 20, "PCMemoryDataChannel::getFragment: Fragment size (bytes)  = " << ed->RODFragmentSize);
257   DEBUG_TEXT(DFDB_ROSFM, 20, "PCMemoryDataChannel::getFragment: Fragment status        = " << ed->RODFragmentStatus);
258 
259   if (m_fragType == 0)
260   {
261     //<+gumh: add time
262     //u_long base = (u_long)(mem_page->address()) ;
263     //u_int *ptr = (u_int *)(base + sizeof(ROBFragment::ROBHeader) + sizeof(RODFragment::RODHeader) + 4 + sizeof(timeval)); // 4 ->     status element
264     //struct timeval tv ;
265     //gettimeofday(&tv, NULL) ;
266     //memcpy(ptr, &tv, sizeof(timeval)) ;
267 
268     //u_int *ptr = (u_int *)(base + sizeof(ROBFragment::ROBHeader) + sizeof(RODFragment::RODHeader) + 4 + sizeof(timeval)); // 4 ->     status element
269     //+>
270 
271     //Create a ROB Fragment in the Buffer and initialize it
272     fragment = new ROBFragment(mem_page, ed->RODFragmentSize, 0, m_sourceIdentifier);
273   }
274 
275   if (m_fragType == 1)
276   {
277     //Create a Full Fragment in the Buffer 
278     fragment = new FullFragment(mem_page);
279     DEBUG_TEXT(DFDB_ROSFM, 20, "PCMemoryDataChannel::getFragment: Full fragment is at " << HEX(fragment));
280   }
281 
282   m_mutex->unlock();
283 
284   DEBUG_TEXT(DFDB_ROSFM, 10, "PCMemoryDataChannel::getFragment: PCMemoryDataChannel:: got fragment with L1ID " << ticket);
285   DEBUG_TEXT(DFDB_ROSFM, 15, "PCMemoryDataChannel::getFragment: done");
286 
287   return(fragment);
288 }