[jira] [Created] (KAFKA-14119) Sensor in metrics has potential thread safety issues

["Eric Wu (Jira)" <ji...@apache.org>]

Eric Wu created KAFKA-14119:
-------------------------------

             Summary: Sensor in metrics has potential thread safety issues
                 Key: KAFKA-14119
                 URL: https://issues.apache.org/jira/browse/KAFKA-14119
             Project: Kafka
          Issue Type: Bug
          Components: metrics
            Reporter: Eric Wu


There are potential issues of a `Sensor` not being protected from race conditions when it [records|https://github.com/apache/kafka/blob/6ac58ac6fcd53a512ea0bc0b3dc66f49870ff0cb/clients/src/main/java/org/apache/kafka/common/metrics/Sensor.java#L230] a value.

It can be reproduced with a unit test, e.g., in `SensorTest`:
{code:java}
@Test
public void testSensorRecordThreadSafety() {
    Time time = new MockTime(0, System.currentTimeMillis(), 0);
    Metrics metrics = new Metrics(time);
    Sensor sensor = metrics.sensor("sensor");
    MetricName metric = new MetricName("test", "test", "test", Collections.emptyMap());
    sensor.add(metric, new Value());

    int totalRequests = 10;
    AtomicInteger count = new AtomicInteger();
    Executor threadPool = Executors.newFixedThreadPool(totalRequests);
    CompletableFuture[] futures = new CompletableFuture[totalRequests];
    for (int i = 0; i < totalRequests; i++) {
        futures[i] = CompletableFuture.runAsync(() -> {
            try {
                Thread.sleep(10); // to make it easier to repro
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
            sensor.record(count.addAndGet(1));
        }, threadPool);
    }
    CompletableFuture.allOf(futures).join();
    
    assertEquals(1, sensor.metrics().size());
    double value = (double) sensor.metrics().get(0).metricValue();
    assertEquals(totalRequests, value);
}{code}
It needs some tweaks to make the fields visible in the test. Given a few runs, the test should fail which demonstrates the thread safety issue.



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