test/hotspot/jtreg/runtime/Thread/ThreadCountLimit.java

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/**
 * @test
 * @summary Stress test that reaches the process limit for thread count, or time limit.
 * @requires os.family != "aix"
 * @key stress
 * @run main/othervm -Xmx1g ThreadCountLimit
 */

/**
 * @test
 * @summary Stress test that reaches the process limit for thread count, or time limit.
 * @requires os.family == "aix"
 * @key stress
 * @run main/othervm -Xmx1g -XX:MaxExpectedDataSegmentSize=16g ThreadCountLimit
 */

import java.util.concurrent.CountDownLatch;
import java.util.ArrayList;

public class ThreadCountLimit {

  static final int TIME_LIMIT_MS = 5000; // Create as many threads as possible in 5 sec

  static class Worker extends Thread {
    private final CountDownLatch startSignal;

    Worker(CountDownLatch startSignal) {
      this.startSignal = startSignal;
    }

    @Override
    public void run() {
      try {
        startSignal.await();
      } catch (InterruptedException e) {
        throw new Error("Unexpected", e);
      }
    }
  }

  public static void main(String[] args) {
    CountDownLatch startSignal = new CountDownLatch(1);
    ArrayList<Worker> workers = new ArrayList<Worker>();

    boolean reachedTimeLimit = false;
    boolean reachedNativeOOM = false;
    int countAtTimeLimit = -1;
    int countAtNativeOOM = -1;

    // This is dangerous loop: it depletes system resources,
    // so doing additional things there that may end up allocating
    // Java/native memory risks failing the VM prematurely.
    // Avoid doing unnecessary calls, printouts, etc.

    int count = 1;
    long start = System.currentTimeMillis();
    try {
      while (true) {
        Worker w = new Worker(startSignal);
        w.start();
        workers.add(w);
        count++;

        long end = System.currentTimeMillis();
        if ((end - start) > TIME_LIMIT_MS) {
          reachedTimeLimit = true;
          countAtTimeLimit = count;
          break;
        }
      }
    } catch (OutOfMemoryError e) {
      if (e.getMessage().contains("unable to create native thread")) {
        // Linux, macOS path
        reachedNativeOOM = true;
        countAtNativeOOM = count;
      } else {
        throw e;
      }
    }

    startSignal.countDown();

    try {
      for (Worker w : workers) {
        w.join();
      }
    } catch (InterruptedException e) {
      throw new Error("Unexpected", e);
    }

    // Now that all threads have joined, we are away from dangerous
    // VM state and have enough memory to perform any other things.
    if (reachedTimeLimit) {
       // Windows path or a system with very large ulimit
       System.out.println("INFO: reached the time limit " + TIME_LIMIT_MS +
                          " ms, with " + countAtTimeLimit + " threads created");
    } else if (reachedNativeOOM) {
       System.out.println("INFO: reached this process thread count limit with " +
                           countAtNativeOOM + " threads created");
    }
  }
}