研究阻塞和非阻塞 IO 时，我心中产生了一些疑问。
我来阅读这里写的一份声明（https://mail-archives.apache.org/mod_mbox/tomcat-users/201402.mbox/%[电子邮件保护]%3E) “即使 NIO HTTP 连接器也必须使用阻塞 IO 来读取请求主体并写入响应：。
有人可以解释一下吗？
其次，我在 tomcat 服务器上运行 jmeter 负载测试，测试我们项目中用于获取用户某些详细信息的 API 之一。最初我每秒发出 2-3 个请求，应用程序能够维持该吞吐量，但当我尝试每秒发出 15-20 个请求时，tomcat 服务器的性能时间呈指数级增长。线程转储显示 Nio 连接器线程正在等待写入数据，请提供解决方案，以免线程被阻塞。
"http-nio-8080-exec-1502" - Thread t@103682
java.lang.Thread.State: TIMED_WAITING
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <400f1e16> (a java.util.concurrent.CountDownLatch$Sync)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedNanos(AbstractQueuedSynchronizer.java:1037)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(AbstractQueuedSynchronizer.java:1328)
at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:277)
at org.apache.tomcat.util.net.NioEndpoint$KeyAttachment.awaitLatch(NioEndpoint.java:1381)
at org.apache.tomcat.util.net.NioEndpoint$KeyAttachment.awaitWriteLatch(NioEndpoint.java:1384)
at org.apache.tomcat.util.net.NioBlockingSelector.write(NioBlockingSelector.java:114)
at org.apache.tomcat.util.net.NioSelectorPool.write(NioSelectorPool.java:172)
at org.apache.coyote.http11.InternalNioOutputBuffer.writeToSocket(InternalNioOutputBuffer.java:139)
at org.apache.coyote.http11.InternalNioOutputBuffer.addToBB(InternalNioOutputBuffer.java:197)
- locked <24b951cc> (a org.apache.coyote.http11.InternalNioOutputBuffer)
at org.apache.coyote.http11.InternalNioOutputBuffer.access$000(InternalNioOutputBuffer.java:41)
at org.apache.coyote.http11.InternalNioOutputBuffer$SocketOutputBuffer.doWrite(InternalNioOutputBuffer.java:320)
at org.apache.coyote.http11.filters.ChunkedOutputFilter.doWrite(ChunkedOutputFilter.java:118)
at org.apache.coyote.http11.AbstractOutputBuffer.doWrite(AbstractOutputBuffer.java:256)
at org.apache.coyote.Response.doWrite(Response.java:491)
at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:391)
at org.apache.tomcat.util.buf.ByteChunk.flushBuffer(ByteChunk.java:426)
at org.apache.tomcat.util.buf.ByteChunk.append(ByteChunk.java:339)
at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:421)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:409)
at org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:97)
at com.fasterxml.jackson.core.json.UTF8JsonGenerator._flushBuffer(UTF8JsonGenerator.java:2039)
at com.fasterxml.jackson.core.json.UTF8JsonGenerator.writeString(UTF8JsonGenerator.java:454)
at com.fasterxml.jackson.databind.ser.std.StringSerializer.serialize(StringSerializer.java:49)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:704)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:704)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:704)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:119)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:79)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:18)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:704)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serializeContents(IndexedListSerializer.java:119)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:79)
at com.fasterxml.jackson.databind.ser.impl.IndexedListSerializer.serialize(IndexedListSerializer.java:18)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:704)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:690)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:292)
at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1429)
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:951)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:264)
at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:100)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:167)
at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:100)
at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:166)
at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:80)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:127)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:806)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:729)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1099)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:672)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
- locked <368bdc01> (a org.apache.tomcat.util.net.NioChannel)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
答案1
我无法告诉你。在堆栈跟踪中，我看到一些 http 和 json 库。我会使用 java 分析器来告诉你应用程序在哪里花费了时间。这样你就应该能够找出代码中的哪一行被阻塞了。或者，你可以在代码中插入日志语句来记录它们被调用的时间。这样你就会看到应用程序在哪里等待。但我猜是 tomcat 调用了你的应用程序（而不是相反），所以可能是等待在你的应用程序之外。