Name: yyT116575 Date: 02/09/2001


Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0-C)
Java HotSpot(TM) Server VM (build 2.0fcs-E, mixed mode)

The keys of ThreadLocals are added to, but never removed from, the
per thread Map. Even if one explicitly sets the value to null the unique
thread local key is still in the Map. This can create a problem for long
running threads.

This is a resubmit of a bug which was previously rejected because I did not
provide a test case. Therefore I'm including the following test case which
will reproduce the problem:

public class test extends Thread {

  public static void main(String[] args) {
    test t = new test();
    t.start();
  }

  private static int counter = 0;

  public void run() {
    System.out.println("Starting");
    try {
      while (true) {
        makeNewThreadLocal();
      }
    } catch (OutOfMemoryError oome) {

      // Print this out in binary format to avoid doing any more allocation
      // after the OutOfMemoryError. I'm too lazy to write a Hex converter
      // for a test case.

      System.out.print("Managed to allocate and release: '");
      System.out.write((counter >>> 24) & 0xFF);
      System.out.write((counter >>> 16) & 0xFF);
      System.out.write((counter >>> 8) & 0xFF);
      System.out.write((counter >>> 0) & 0xFF);
      System.out.println("' ThreadLocals before running out of memory");

      throw oome;
    }
  }

  // Note that when this method returns both the ThreadLocal and its value
  // will be candidates for collection. The bug is that even when the
  // ThreadLocal is collected its key remains in the threadLocals Map.

  private void makeNewThreadLocal() {
    ThreadLocal t = new ThreadLocal();
    t.set(new Object());
    t.set(null);
    ++counter;
  }

}


When run this program produces an out of memory error:

Starting
Managed to allocate and release: ' ^Pj^C' ThreadLocals before running out of memory
java.lang.OutOfMemoryError
        <<no stack trace available>>
(Review ID: 116693)
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