java - DeadlineExceededException 如何在 Google App Engine for Java 中实现？

Question

在 Google App Engine 上的应用必须具有在 30 秒内返回响应数据的 Web 请求。当超过这个时间时，会抛出一个DeadlineExceededException异常:

/time.jsp
java.lang.ClassCastException: com.google.apphosting.api.DeadlineExceededException cannot be cast to javax.servlet.ServletException
    at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:754)
    at org.apache.jsp.time_jsp._jspService(time_jsp.java:66)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1093)
    at com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:712)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
    at com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:237)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
    at org.mortbay.jetty.Server.handle(Server.java:313)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:506)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:830)
    at com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
    at com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:125)
    at com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235)
    at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4755)
    at com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4753)
    at com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24)
    at com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:359)
    at com.google.net.rpc.impl.Server$2.run(Server.java:800)
    at com.google.tracing.LocalTraceSpanRunnable.run(LocalTraceSpanRunnable.java:56)
    at com.google.tracing.LocalTraceSpanBuilder.internalContinueSpan(LocalTraceSpanBuilder.java:510)
    at com.google.net.rpc.impl.Server.startRpc(Server.java:756)
    at com.google.net.rpc.impl.Server.processRequest(Server.java:348)
    at com.google.net.rpc.impl.ServerConnection.messageReceived(ServerConnection.java:459)
    at com.google.net.rpc.impl.RpcConnection.parseMessages(RpcConnection.java:319)
    at com.google.net.rpc.impl.RpcConnection.dataReceived(RpcConnection.java:290)
    at com.google.net.async.Connection.handleReadEvent(Connection.java:419)
    at com.google.net.async.EventDispatcher.processNetworkEvents(EventDispatcher.java:762)
    at com.google.net.async.EventDispatcher.internalLoop(EventDispatcher.java:207)
    at com.google.net.async.EventDispatcher.loop(EventDispatcher.java:101)
    at com.google.net.rpc.RpcService.runUntilServerShutdown(RpcService.java:251)
    at com.google.apphosting.runtime.JavaRuntime$RpcRunnable.run(JavaRuntime.java:373)
    at java.lang.Thread.run(Unknown Source)

这是怎么做到的？你有任何开源代码吗？

Answer 1

The Request Timer

A request handler has a limited amount of time to generate and return a response to a request, typically around 30 seconds. Once the deadline has been reached, the request handler is interrupted.

The Java runtime environment interrupts the servlet by throwing a com.google.apphosting.api.DeadlineExceededException. If the request handler does not catch this exception, as with all uncaught exceptions, the runtime environment will return an HTTP 500 server error to the client.

The request handler can catch this error to customize the response. The runtime environment gives the request handler a little bit more time (less than a second) after raising the exception to prepare a custom response.

While a request can take as long as 30 seconds to respond, App Engine is optimized for applications with short-lived requests, typically those that take a few hundred milliseconds. An efficient app responds quickly for the majority of requests. An app that doesn't will not scale well with App Engine's infrastructure.

部分运行时==不使用线程。这个功能肯定是对虚拟机的修改，我不会屏住呼吸等待源代码。