Java多线程文件保存

Question

I have an app that created multiple endless threads. Each thread reads some info and I created some tasks using thread pool (which is fine).

I have added additional functions that handle arrays, when it finishes, its send those ArrayList s to new thread that save those lists as files. I have implemented the saving in 3 ways and only one of which succeeds. I would like to know why the other 2 ways did not.

1. I created a thread (via new Thread(Runnable) ) and gave it the array and name of the file. In the thread constructor I create the PrintWriter and saved the files. It ran without any problems. ( I have 1-10 file save threads runing in parallel).

2. If I place the save code outputStream.println(aLog); in the Run method, it never reaches it and after the constructor finishes the thread exit.

3. I place the created runnables (file save) in a thread pool (and code for saving is in the run() method). When I send just 1 task (1 file to save), all is fine. More than 1 task is being added to the pool (very quickly), exceptions is created (in debug time I can see that all needed info is available) and some of the files are not saved.

Can one explain the difference behavior? Thanks

Please see code below. (starting with function that is being part of an endless thread class that also place some tasks in the pool), the pool created in the endless thread: ExecutorService iPool = Executors.newCachedThreadPool();

private void logRate(double r1,int ind){
 historicalData.clear();
    for (int i = 499; i>0; i--){
      // some Code

     Data.add(0,array1[ind][i][0] + "," + array1[ind][i][1] + "," + 
                          array1[ind][i][2] + "," + array1[ind][i][3] + "," +
                          array2[ind][i] + "\n" );
     }
      // first item
      array1[ind][0][0] = r1; 
      array1[ind][0][1] = array1[ind][0][0] ;
      array1[ind][0][2] = array1[ind][0][0] ;
      array2[ind][0] = new SimpleDateFormat("HH:mm:ss yyyy_MM_dd").format(today); 

      Data.add(0,r1+","+r1+","+r1+","+r1+ "," + array2[ind][0] + '\n') ;

      // save the log send it to the pool (this is case 3)
      //iPool.submit(new FeedLogger(fName,Integer.toString(ind),Data));
      // Case 1 and 2 
      Thread fl = new Thread(new FeedLogger(fName,Integer.toString(ind),Data)) ;
    }

here is the FeedLogger class:

public class FeedLogger implements Runnable{
private List<String> fLog = new ArrayList<>() ;
PrintWriter outputStream = null;
String asName,asPathName;

public FeedLogger(String aName,String ind, List<String> fLog) {
this.fLog = fLog;
this.asName = aName;

try {
    asPathName = System.getProperty("user.dir") + "\\AsLogs\\"  + asName + "\\Feed" + ind 
                                    + ".log" ;

     outputStream = new PrintWriter(new FileWriter(asPathName));
     outputStream.println(fLog); Case 1 all is fine
     outputStream.flush(); // Case 1 all is fine
     outputStream.close(); Case 1 all is fine

}
catch (Exception ex) {
    JavaFXApplication2.logger.log(Level.SEVERE, null,asName + ex.getMessage());
 }
}

@Override
public void run()
{
 try{
    outputStream.println(fLog); // Cas2 --> not reaching this code, Case3 (as task) create 
                                                     exception when we have multiple tasks
    outputStream.flush();
    } 
  catch (Exception e) {
      System.out.println("err in file save e=" + e.getMessage() + asPathName + " feed size=" +  
                          fLog.size()); 
      JavaFXApplication2.logger.log(Level.ALL, null,asName + e.getMessage());
  } 

    finally {if (outputStream != null) {outputStream.close();}}
    }
  } 

Answer 1

您需要在Thread实例上调用start()使其实际执行某些操作。