线上有一个音讯生产服务 xxx-consumer，应用 spring-kafka 框架，主线程批量从生产队列（kafka）拉取交易系统生产的音讯，而后提交到子线程池中挨个解决生产。
public abstract class AbstractMessageDispatchListener implements
BatchAcknowledgingMessageListener<String, Msg>, ApplicationListener<ApplicationReadyEvent> {
private ThreadPoolExecutor executor;
public abstract MessageWorker chooseWorker(ConsumerRecord<String, Msg> data);
@Override
public void onMessage(List<ConsumerRecord<String, Msg>> datas, Acknowledgment acknowledgment) {List<Future<?>> futureList = new ArrayList<>(datas.size());
try {CountDownLatch countDownLatch = new CountDownLatch(datas.size());
for (ConsumerRecord<String, Msg> data : datas) {Future<?> future = executor.submit(new Worker(data, countDownLatch));
futureList.add(future);
}
countDownLatch.await(20000L - 2000, TimeUnit.MILLISECONDS);
long countDownLatchCount = countDownLatch.getCount();
if (countDownLatchCount > 0) {return;}
acknowledgment.acknowledge();} catch (Exception e) {logger.error("onMessage error", e);
} finally {for (Future<?> future : futureList) {if (future.isDone() || future.isCancelled()) {continue;}
future.cancel(true);
}
}
}
@Override
public void onApplicationEvent(ApplicationReadyEvent event) {ThreadFactoryBuilder builder = new ThreadFactoryBuilder();
builder.setNameFormat(this.getClass().getSimpleName() + "-pool-%d");
builder.setDaemon(false);
executor = new ThreadPoolExecutor(12,
12 * 2,
60L,
TimeUnit.SECONDS,
new ArrayBlockingQueue<>(100),
builder.build());
}
private class Worker implements Runnable {
private ConsumerRecord<String, Msg> data;
private CountDownLatch countDownLatch;
Worker(ConsumerRecord<String, Msg> data, CountDownLatch countDownLatch) {
this.data = data;
this.countDownLatch = countDownLatch;
}
@Override
public void run() {
try {MessageWorker worker = chooseWorker(data);
worker.work(data.value());
} finally {countDownLatch.countDown();
}
}
}
}1. 问题背景
有一天早上 xxx-consumer 服务呈现大量报警，人工排查发现 30w+ 的音讯未解决，业务日志失常，gc 日志有大量 Full gc，初步判断因为 Full gc 导致音讯解决慢，大量的音讯积压。
2. 堆栈剖析
查看了近一个月的 JVM 内存信息，发现老年代内存无奈被回收（9 月 22 号的降落是因为服务有一次上线重启），初步判断产生了内存透露。
通过 <jmap -dump:format=b,file=/home/work/app/xxx-consumer/logs/jmap_dump.hprof -F> 命令导出内存快照，应用 Memory Analyzer 解析内存快照文件 jmap_dump.hprof，发现有很显著的内存透露提醒：
进一步查看线程细节，发现创立了大量的 ThreadLocalScope 对象且循环援用：
同时咱们也看到了分布式追踪（dd-trace-java）jar 包中的 FakeSpan 类，初步判断是 dd-trace-java 中自研扩大的 kafka 插件存在内存透露 bug。
3. 代码剖析
持续查看 dd-trace-java 中 kafka 插件的代码，其解决流程如下：
第一批音讯
- （SpringKafkaConsumerInstrumentation:L22）BatchAcknowledgingMessageListener.onMessage 进入时，主线程会创立一个 scope00=ThreadLocalScope（Type_BatchMessageListener_Value，toRestore=null）
- （ExecutorInstrumentation:L21L47）音讯被 submit 到线程池中解决时，子线程会创立一个 scope10=ThreadLocalScope（Type_BatchMessageListener_Value，toRestore=null）
- （SpringKafkaConsumerInstrumentation:L68）子线程解决音讯时（ConsumerRecord.value），会创立一个 scope11=ThreadLocalScope（Type_ConsumberRecord_Value，toRestore=scope10）
- （ExecutorInstrumentation:L54）子线程解决完音讯后，执行 scope10.close()，而 scopeManager.tlsScope.get()=scope11，命中 ThreadLocalScope:L19，scope10 和 scope11 均无奈被 GC
- （SpringKafkaConsumerInstrumentation:L42）BatchAcknowledgingMessageListener.onMessage 退出时，主线程会执行 scope00.close()，scope00 会被 GC
第二批音讯
- （SpringKafkaConsumerInstrumentation:L22）BatchAcknowledgingMessageListener.onMessage 进入时，主线程会创立一个 scope01=ThreadLocalScope（Type_BatchMessageListener_Value，toRestore=null）
- （ExecutorInstrumentation:L21L47）音讯被 submit 到线程池中解决时，子线程会创立一个 scope12=ThreadLocalScope（Type_BatchMessageListener_Value，toRestore=scope11）
- （SpringKafkaConsumerInstrumentation:L68）子线程解决音讯时（ConsumerRecord.value），会创立一个 scope13=ThreadLocalScope（Type_ConsumberRecord_Value，toRestore=scope12）
- （ExecutorInstrumentation:L54）子线程解决完音讯后，执行 scope12.close()，而 scopeManager.tlsScope.get()=scope13，命中 ThreadLocalScope:L19，scope12 和 scope13 均无奈被 GC
- （SpringKafkaConsumerInstrumentation:L42）BatchAcknowledgingMessageListener.onMessage 退出时，主线程会执行 scope01.close()，scope01 会被 GC
从上能够看到，主线程创立的 ThreadLocalScope 能被正确 GC，而线程池中创立的 ThreadLocalScope 被循环援用，无奈被正确 GC，从而造成内存透露。
@AutoService(Instrumenter.class)
public final class SpringKafkaConsumerInstrumentation extends Instrumenter.Configurable {
@Override
public AgentBuilder apply(final AgentBuilder agentBuilder) {
return agentBuilder
.type(hasSuperType(named("org.springframework.kafka.listener.BatchAcknowledgingMessageListener")))
.transform(DDAdvice.create().advice(isMethod().and(isPublic()).and(named("onMessage")),
BatchMessageListenerAdvice.class.getName()))
.type(named("org.apache.kafka.clients.consumer.ConsumerRecord"))
.transform(DDAdvice.create().advice(isMethod().and(isPublic()).and(named("value")),
RecoredValueAdvice.class.getName()))
.asDecorator();}
public static class BatchMessageListenerAdvice {@Advice.OnMethodEnter(suppress = Throwable.class)
public static Scope before() {FakeSpan span = new FakeSpan();
span.setKind(FakeSpan.Type_BatchMessageListener_Value);
Scope scope = GlobalTracer.get().scopeManager().activate(span, false);
return scope;
}
@Advice.OnMethodExit(suppress = Throwable.class)
public static void after(@Advice.Enter Scope scope) {while (true) {Span span = GlobalTracer.get().activeSpan();
if (span != null && span instanceof FakeSpan) {FakeSpan fakeSpan = (FakeSpan) span;
if (fakeSpan.getKind().equals(FakeSpan.Type_ConsumberRecord_Value)) {GlobalTracer.get().scopeManager().active().close();} else {break;}
} else {break;}
}
if (scope != null) {scope.close();
}
}
}
public static class RecoredValueAdvice {@Advice.OnMethodEnter(suppress = Throwable.class)
public static void before(@Advice.This ConsumerRecord record) {Span activeSpan = GlobalTracer.get().activeSpan();
if (activeSpan instanceof FakeSpan) {FakeSpan proxy = (FakeSpan) activeSpan;
if (proxy.getKind().equals(FakeSpan.Type_ConsumberRecord_Value)) {GlobalTracer.get().scopeManager().active().close();
activeSpan = GlobalTracer.get().activeSpan();
if (activeSpan instanceof FakeSpan) {proxy = (FakeSpan) activeSpan;
}
}
if (proxy.getKind().equals(FakeSpan.Type_BatchMessageListener_Value)) {final SpanContext spanContext = TracingKafkaUtils.extractSecond(record.headers(), GlobalTracer.get());
if (spanContext != null) {FakeSpan consumerProxy = new FakeSpan();
consumerProxy.setContext(spanContext);
consumerProxy.setKind(FakeSpan.Type_ConsumberRecord_Value);
GlobalTracer.get().scopeManager().activate(consumerProxy, false);
}
}
}
}
}
}@AutoService(Instrumenter.class)
public final class ExecutorInstrumentation extends Instrumenter.Configurable {
@Override
public AgentBuilder apply(final AgentBuilder agentBuilder) {
return agentBuilder
.type(not(isInterface()).and(hasSuperType(named(ExecutorService.class.getName()))))
.transform(DDAdvice.create().advice(named("submit").and(takesArgument(0, Runnable.class)),
SubmitTracedRunnableAdvice.class.getName()))
.asDecorator();}
public static class SubmitTracedRunnableAdvice {@Advice.OnMethodEnter(suppress = Throwable.class)
public static TracedRunnable wrapJob(
@Advice.This Object dis,
@Advice.Argument(value = 0, readOnly = false) Runnable task) {if (task != null && (!dis.getClass().getName().startsWith("slick.util.AsyncExecutor"))) {task = new TracedRunnable(task, GlobalTracer.get());
return (TracedRunnable) task;
}
return null;
}
}
public static class TracedRunnable implements Runnable {
private final Runnable delegate;
private final Span span;
private final Tracer tracer;
public TracedRunnable(Runnable delegate, Tracer tracer) {
this.delegate = delegate;
this.tracer = tracer;
if (tracer != null) {this.span = tracer.activeSpan();
} else {this.span = null;}
}
@Override
public void run() {
Scope scope = null;
if (span != null && tracer != null) {scope = tracer.scopeManager().activate(span, false);
}
try {delegate.run();
} finally {if (scope != null) {scope.close();
}
}
}
}
}public class ThreadLocalScopeManager implements ScopeManager {final ThreadLocal<ThreadLocalScope> tlsScope = new ThreadLocal<ThreadLocalScope>();
@Override
public Scope activate(Span span, boolean finishOnClose) {return new ThreadLocalScope(this, span, finishOnClose);
}
@Override
public Scope active() {return tlsScope.get();
}
}public class ThreadLocalScope implements Scope {
private final ThreadLocalScopeManager scopeManager;
private final Span wrapped;
private final boolean finishOnClose;
private final ThreadLocalScope toRestore;
ThreadLocalScope(ThreadLocalScopeManager scopeManager, Span wrapped, boolean finishOnClose) {
this.scopeManager = scopeManager;
this.wrapped = wrapped;
this.finishOnClose = finishOnClose;
this.toRestore = scopeManager.tlsScope.get();
scopeManager.tlsScope.set(this);
}
@Override
public void close() {if (scopeManager.tlsScope.get() != this) {
// This shouldn't happen if users call methods in the expected order. Bail out.
return;
}
if (finishOnClose) {wrapped.finish();
}
scopeManager.tlsScope.set(toRestore);
}
@Override
public Span span() {return wrapped;}
}End
RecoredValueAdvice 没有销毁本人创立的对象，而是寄希望于 BatchMessageListenerAdvice 去销毁。
但（SpringKafkaConsumerInstrumentation:L27）BatchAcknowledgingMessageListener.onMessage 退出时，只会 close 主线程创立的 ThreadLocalScope，不会 close 线程池中创立的 ThreadLocalScope，导致子线程创立的 ThreadLocalScope 被循环援用，无奈被正确 GC，从而造成内存透露。