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[fix][Java Client] Fix thread safety issue of
LastCumulativeAck (ap…
…ache#16072) ### Motivation There were several issues caused by the thread safe issue of `LastCumulativeAck`, see: - apache#10586 - apache#12343 The root cause is that `LastCumulativeAck` could be accessed by different threads, especially in `flushAsync` method. But the fields are accessed directly and no thread safety can be guaranteed. In addition, the current `LastCumulativeAck` class was added in apache#8996 to hold two object references, but this modification is wrong. Before apache#8996, there are two CAS operations in `doCumulativeAck` method in case it's called concurretly. Though the composite CAS operation is not atomic. However, after apache#8996, only CAS operation was performed but it's compared with a `LastCumulativeAck` object, not the two fields (`messageId` and `bitSetRecyclable`). There is another issue that it uses a flag `cumulativeAckFlushRequired` to mark if `lastCumulativeAck` should flush. However, if `flushAsync` was called concurrently, both would send ACK commands to broker. ### Modifications To solve the thread safety issue, this PR move the `LastCumulativeAck` out of the `PersistentAcknowledgmentsGroupingTracker` to disable directly access to the internal fields. Then, the following synchronized methods were added to guarantee the thread safety: - `update`: Guarantee the safe write operations. It also recycles the `BitSetRecyclable` object before assigning new values and indicates itself can be flushed. - `flush`: If it can be flushed, return a thread local `LastCumulativeAck` instance that contains the message ID and the bit set. The bit set is deep copied to avoid the original reference being recycled in another `update` call. In addition, since the `messageId` field is volatile, the `getMessageId` method can always retrieve the latest reference. `LastCumulativeAckTest` is added to verify the sematics above. Based on the new design, we can only maintain a `LastCumulativeAck` field in `PersistentAcknowledgmentsGroupingTracker` and call the related methods in `doCumulativeAck` and `flushAsync`. It also fixes the problem that two concurrent `flushAsync` calls might send the same ACK command twice.
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pulsar-client/src/test/java/org/apache/pulsar/client/impl/LastCumulativeAckTest.java
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| /** | ||
| * Licensed to the Apache Software Foundation (ASF) under one | ||
| * or more contributor license agreements. See the NOTICE file | ||
| * distributed with this work for additional information | ||
| * regarding copyright ownership. The ASF licenses this file | ||
| * to you under the Apache License, Version 2.0 (the | ||
| * "License"); you may not use this file except in compliance | ||
| * with the License. You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, | ||
| * software distributed under the License is distributed on an | ||
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | ||
| * KIND, either express or implied. See the License for the | ||
| * specific language governing permissions and limitations | ||
| * under the License. | ||
| */ | ||
| package org.apache.pulsar.client.impl; | ||
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| import static org.testng.Assert.assertEquals; | ||
| import static org.testng.Assert.assertFalse; | ||
| import static org.testng.Assert.assertNotSame; | ||
| import static org.testng.Assert.assertNull; | ||
| import static org.testng.Assert.assertSame; | ||
| import static org.testng.Assert.assertTrue; | ||
| import org.apache.pulsar.common.util.collections.BitSetRecyclable; | ||
| import org.testng.annotations.Test; | ||
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| public class LastCumulativeAckTest { | ||
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| @Test | ||
| public void testUpdate() { | ||
| final LastCumulativeAck lastCumulativeAck = new LastCumulativeAck(); | ||
| assertFalse(lastCumulativeAck.isFlushRequired()); | ||
| assertEquals(lastCumulativeAck.getMessageId(), LastCumulativeAck.DEFAULT_MESSAGE_ID); | ||
| assertNull(lastCumulativeAck.getBitSetRecyclable()); | ||
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| final MessageIdImpl messageId1 = new MessageIdImpl(0L, 1L, 10); | ||
| final BitSetRecyclable bitSetRecyclable1 = BitSetRecyclable.create(); | ||
| bitSetRecyclable1.set(0, 3); | ||
| lastCumulativeAck.update(messageId1, bitSetRecyclable1); | ||
| assertTrue(lastCumulativeAck.isFlushRequired()); | ||
| assertSame(lastCumulativeAck.getMessageId(), messageId1); | ||
| assertSame(lastCumulativeAck.getBitSetRecyclable(), bitSetRecyclable1); | ||
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| final MessageIdImpl messageId2 = new MessageIdImpl(0L, 2L, 8); | ||
| lastCumulativeAck.update(messageId2, bitSetRecyclable1); | ||
| // bitSetRecyclable1 is not recycled | ||
| assertEquals(bitSetRecyclable1.toString(), "{0, 1, 2}"); | ||
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| final BitSetRecyclable bitSetRecyclable2 = BitSetRecyclable.create(); | ||
| bitSetRecyclable2.set(0, 2); | ||
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| // `update()` only accepts a newer message ID, so this call here has no side effect | ||
| lastCumulativeAck.update(messageId2, bitSetRecyclable2); | ||
| assertSame(lastCumulativeAck.getBitSetRecyclable(), bitSetRecyclable1); | ||
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| final MessageIdImpl messageId3 = new MessageIdImpl(0L, 3L, 9); | ||
| lastCumulativeAck.update(messageId3, bitSetRecyclable2); | ||
| // bitSetRecyclable1 is recycled because it's replaced in `update` | ||
| assertEquals(bitSetRecyclable1.toString(), "{}"); | ||
| assertSame(lastCumulativeAck.getMessageId(), messageId3); | ||
| assertSame(lastCumulativeAck.getBitSetRecyclable(), bitSetRecyclable2); | ||
| bitSetRecyclable2.recycle(); | ||
| } | ||
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| @Test | ||
| public void testFlush() { | ||
| final LastCumulativeAck lastCumulativeAck = new LastCumulativeAck(); | ||
| assertNull(lastCumulativeAck.flush()); | ||
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| final MessageIdImpl messageId = new MessageIdImpl(0L, 1L, 3); | ||
| final BitSetRecyclable bitSetRecyclable = BitSetRecyclable.create(); | ||
| bitSetRecyclable.set(0, 3); | ||
| lastCumulativeAck.update(messageId, bitSetRecyclable); | ||
| assertTrue(lastCumulativeAck.isFlushRequired()); | ||
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| final LastCumulativeAck lastCumulativeAckToFlush = lastCumulativeAck.flush(); | ||
| assertFalse(lastCumulativeAck.isFlushRequired()); | ||
| assertSame(lastCumulativeAckToFlush.getMessageId(), messageId); | ||
| assertNotSame(lastCumulativeAckToFlush.getBitSetRecyclable(), bitSetRecyclable); | ||
| assertEquals(lastCumulativeAckToFlush.getBitSetRecyclable(), bitSetRecyclable); | ||
| } | ||
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| } |