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PODeleting And Reconstructing Singleton in C++
 

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    <p>I have an application which runs on a controlling hardware connected with different sensors. On loading the application, it checks the individual sensors one by one to see whether there is proper communication with the sensor according to predefined protocol or not.</p> <p>Now, I have implemented the code for checking the individual sensor communication as a singleton thread and following is the run function, it used select system call and pipe for interprocess communication to signal the end of thread.</p> <pre><code>void SensorClass::run() { mFdWind=mPort-&gt;GetFileDescriptor(); fd_set readfs; int max_fd = (mFdWind &gt; gPipeFdWind[0] ? mFdWind : gPipeFdWind[0]) + 1; int res; mFrameCorrect=false; qDebug("BEFORE WHILE"); while(true) { qDebug("\n IN WHILE LOOP"); usleep(50); FD_ZERO(&amp;readfs); FD_SET(mFdWind,&amp;readfs); FD_SET(gPipeFdWind[0],&amp;readfs); res=select(max_fd,&amp;readfs,NULL,NULL,NULL); if(res &lt; 0) perror("Select Failed"); else if(res == 0) puts("TIMEOUT"); else { if(FD_ISSET(mFdWind,&amp;readfs)) { puts("*************** RECEIVED DATA ****************"); mFrameCorrect=false; FlushBuf(); //int n=mPort-&gt;ReadPort(mBuf,100); int n=mPort-&gt;ReadPort(mBuf,100); if(n&gt;0) { Count++; QString str((const char*)mBuf); //qDebug("\n %s",qPrintable(str)); //See if the Header of the frame is valid if(IsHeaderValid(str)) { if( (!IsCommaCountOk(str)) || (!IsChecksumOk(str,mBuf)) || (!CalculateCommaIndexes(str)) ) { qDebug("\n not ok"); mFrameCorrect=false; } //if frame is incorrect else { qDebug("\n OK"); mFrameCorrect=true; }//if frame is correct(checksum etc are ok) }//else if header is ok }//if n &gt; 0 }//if data received FD_ISSET if(FD_ISSET(gPipeFdWind[0],&amp;readfs)) break; }//end nested else res not &lt;= 0 }//infinite loop } </code></pre> <p>The above thread is run started from the main GUI thread. This runs fine. The problem is I have given an option to the user to retest the subsystem at will. For this I delete the singleton instance using </p> <pre><code>delete SensorClass::instance(); </code></pre> <p>and then restart the singleton using</p> <pre><code>SensorClass::instace()-&gt;start(); </code></pre> <p>The problem is this time the control comes out of while loop in run() function immedeately upon entering the while loop, my guess is the pipe read has again read from the write pipe which was written to the last time. I have tried to use the fflush() to clear out the I/O but no luck. My question is </p> <ol> <li><p>Am I thinking on the right track?</p></li> <li><p>If yes then how do we clear out the pipes?</p></li> <li><p>If not can anyone suggest why is the selective retest not working?</p></li> </ol> <p>Thanks in advance..</p>
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    1. CODoes "at will" include when the thread is still running? Where is `gPipeFdWind` defined? In particular, is it a global, a class variable or an instance variable?
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    2. COit is a global variable and defined and declared properly with extern statement.
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    3. COThen it's definitely causing the while loop to exit on first iteration. Since you aren't reading the incoming data, it stays ready for reading and the `select()` will return immediately with `gPipeFdWind[0]` in `readfs`.
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