Race condition in Atmosphere when initializing two VaadinServlets at the same time

[vaadin-bot]

Originally by @Artur-

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One way to reproduce is to set a breakpoint in PushRequestHandler's constructor and DefaultBroadcasterFactory.lookup(Class,Object,boolean,boolean) . Then open two URLs mapped to different servlets, e.g. /integration and /run/BasicPush. The race condition comes from addAtmosphereHandler. Depending on which thread enters the synchronized block in lookup first, it either works or throws an exception:

Apr 2, 2014 7:58:26 PM org.atmosphere.cpr.AtmosphereFramework interceptor
INFO: Installed AtmosphereInterceptor  Track Message Size Interceptor using | with priority BEFORE_DEFAULT 
Apr 2, 2014 7:58:34 PM org.atmosphere.cpr.AtmosphereFramework configureBroadcaster
SEVERE: Unable to configure Broadcaster/Factory/Cache
java.lang.IllegalStateException: Broadcaster already exists /*. Use BroadcasterFactory.lookup instead
	at org.atmosphere.cpr.DefaultBroadcasterFactory.lookup(DefaultBroadcasterFactory.java:189)
	at org.atmosphere.cpr.DefaultBroadcasterFactory.get(DefaultBroadcasterFactory.java:121)
	at org.atmosphere.cpr.DefaultBroadcasterFactory.get(DefaultBroadcasterFactory.java:108)
	at org.atmosphere.cpr.AtmosphereFramework.configureBroadcaster(AtmosphereFramework.java:1041)
	at org.atmosphere.cpr.AtmosphereFramework.init(AtmosphereFramework.java:714)
	at org.atmosphere.cpr.AtmosphereFramework.init(AtmosphereFramework.java:616)
	at com.vaadin.server.communication.PushRequestHandler.<init>(PushRequestHandler.java:113)
	at com.vaadin.server.VaadinServletService.createRequestHandlers(VaadinServletService.java:92)
	at com.vaadin.server.VaadinService.init(VaadinService.java:179)
	at com.vaadin.server.VaadinServlet.createServletService(VaadinServlet.java:190)
	at com.vaadin.server.VaadinServlet.init(VaadinServlet.java:96)
	at com.vaadin.server.LegacyVaadinServlet.init(LegacyVaadinServlet.java:48)
	at com.vaadin.launcher.ApplicationRunnerServlet.init(ApplicationRunnerServlet.java:60)
	at org.eclipse.jetty.servlet.ServletHolder.initServlet(ServletHolder.java:519)
	at org.eclipse.jetty.servlet.ServletHolder.getServlet(ServletHolder.java:402)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:642)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:457)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
	at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:557)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1075)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:384)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1009)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
	at org.eclipse.jetty.server.Server.handle(Server.java:368)
	at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:488)
	at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:932)
	at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:994)
	at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:640)
	at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
	at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:628)
	at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
	at java.lang.Thread.run(Thread.java:695)
Apr 2, 2014 7:58:34 PM org.atmosphere.cpr.AtmosphereFramework autoDetectWebSocketHandler
INFO: Auto detecting WebSocketHandler in /WEB-INF/classes/

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Imported from https://dev.vaadin.com/ issue #13528

[vaadin-bot]

Originally by @Artur-

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Atmosphere ticket: Atmosphere/atmosphere#1543

[vaadin-bot]

Originally by @Artur-

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Fixed with a workaround until the Atmosphere issue is fixed

[vaadin-bot]

Originally by CodingFabian

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The same code is in 7.1.x - i guess it should be backported?