java - Why is this program creating more threads than possible? -

this custom udtf in hive query, createlogtable udtf class using temp testing. creating 1 thread per file downloaded amazon s3 , waiting until thread becomes available before allocating file thread.

main test logic:

createlogtable clt = new createlogtable();  int numthreads = 2; int index = 0; downloadfilethread[] dlthreads = new downloadfilethread[numthreads]; (s3objectsummary osummary : bucketkeys.getobjectsummaries()) {     while (dlthreads[index] != null && dlthreads[index].isalive()) {         index += 1;         index = index % numthreads;     }     dlthreads[index] = new downloadfilethread(clt , getbucket(osummary.getbucketname() + "/"                     + osummary.getkey()), getfile(osummary.getkey()), index);     dlthreads[index].start();     index += 1;     index = index % numthreads; } 

thread class (run() method):

try {     system.out.println("creating thread " + this.threadnum);     this.fileobj = this.s3client.getobject(new getobjectrequest(this.filepath, this.filename));     this.filein = new scanner(new gzipinputstream(this.fileobj.getobjectcontent()));     while (this.filein.hasnext()) {                  this.parent.forwardtotable(filein.nextline());     }     system.out.println("finished " + this.threadnum); } catch (throwable e) {     system.out.println("downloading of " + this.filename + " failed."); } 

the while loop before thread creation should looping until finds null thread or dead thread until exits loop, in case new thread created , started. since included logging console, able observe process, output unexpected:

creating thread 0 creating thread 1 creating thread 0 creating thread 1 creating thread 0 creating thread 1 creating thread 0 ... creating thread 1 creating thread 0 creating thread 1 finished 0 finished 1 finished 1 finished 0 finished 1 finished 1 ... finished 0 finished 1 finished 0 finished 1 

the above first few lines of output. issue more 2 threads created before threads complete tasks.

why happening , how can fix this?

try see example:

public static void main(string[] args) {         executorservice executor = executors.newfixedthreadpool(5);         (int = 0; < 10; i++) {             runnable worker = new workerthread("" + i);             executor.execute(worker);           }         executor.shutdown();         while (!executor.isterminated()) {         }         system.out.println("finished threads"); } 

it's thread pool using java 8. simple , esay way make using executors. staraight forward way make it.