ab7accb2de
Motivation: In MemoryRegionCache.Entry we use the Recycler to reduce GC pressure and churn. The problem is that these will also be recycled when the PoolThreadCache is collected and finalize() is called. This then can have the effect that we try to load class but the WebApp is already stoped. This will produce an stacktrace like this on Tomcat: ``` 19-Mar-2019 15:53:21.351 INFO [Finalizer] org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading Illegal access: this web application instance has been stopped already. Could not load [java.util.WeakHashMap]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access. java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [java.util.WeakHashMap]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access. at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1383) at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1371) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1186) at io.netty.util.Recycler$3.initialValue(Recycler.java:233) at io.netty.util.Recycler$3.initialValue(Recycler.java:230) at io.netty.util.concurrent.FastThreadLocal.initialize(FastThreadLocal.java:188) at io.netty.util.concurrent.FastThreadLocal.get(FastThreadLocal.java:142) at io.netty.util.Recycler$Stack.pushLater(Recycler.java:624) at io.netty.util.Recycler$Stack.push(Recycler.java:597) at io.netty.util.Recycler$DefaultHandle.recycle(Recycler.java:225) at io.netty.buffer.PoolThreadCache$MemoryRegionCache$Entry.recycle(PoolThreadCache.java:478) at io.netty.buffer.PoolThreadCache$MemoryRegionCache.freeEntry(PoolThreadCache.java:459) at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:430) at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:422) at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:279) at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:270) at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:241) at io.netty.buffer.PoolThreadCache.finalize(PoolThreadCache.java:230) at java.lang.System$2.invokeFinalize(System.java:1270) at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:102) at java.lang.ref.Finalizer.access$100(Finalizer.java:34) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:217) ``` Beside this we also need to ensure we not try to lazy load SizeClass when the finalizer is used as it may not be present anymore if the ClassLoader is already destroyed. This would produce an error like: ``` 20-Mar-2019 11:26:35.254 INFO [Finalizer] org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading Illegal access: this web application instance has been stopped already. Could not load [io.netty.buffer.PoolArena$1]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access. java.lang.IllegalStateException: Illegal access: this web application instance has been stopped already. Could not load [io.netty.buffer.PoolArena$1]. The following stack trace is thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access. at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForResourceLoading(WebappClassLoaderBase.java:1383) at org.apache.catalina.loader.WebappClassLoaderBase.checkStateForClassLoading(WebappClassLoaderBase.java:1371) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1186) at io.netty.buffer.PoolArena.freeChunk(PoolArena.java:287) at io.netty.buffer.PoolThreadCache$MemoryRegionCache.freeEntry(PoolThreadCache.java:464) at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:429) at io.netty.buffer.PoolThreadCache$MemoryRegionCache.free(PoolThreadCache.java:421) at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:278) at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:269) at io.netty.buffer.PoolThreadCache.free(PoolThreadCache.java:240) at io.netty.buffer.PoolThreadCache.finalize(PoolThreadCache.java:229) at java.lang.System$2.invokeFinalize(System.java:1270) at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:102) at java.lang.ref.Finalizer.access$100(Finalizer.java:34) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:217) ``` Modifications: - Only try to put the Entry back into the Recycler if the PoolThredCache is not destroyed because of the finalizer. - Only try to access SizeClass if not triggered by finalizer. Result: No IllegalStateException anymoe when a webapp is reloaded in Tomcat that uses netty and uses the PooledByteBufAllocator.
Netty Project
Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients.
Links
How to build
For the detailed information about building and developing Netty, please visit the developer guide. This page only gives very basic information.
You require the following to build Netty:
- Latest stable Oracle JDK 7
- Latest stable Apache Maven
- If you are on Linux, you need additional development packages installed on your system, because you'll build the native transport.
Note that this is build-time requirement. JDK 5 (for 3.x) or 6 (for 4.0+) is enough to run your Netty-based application.
Branches to look
Development of all versions takes place in each branch whose name is identical to <majorVersion>.<minorVersion>. For example, the development of 3.9 and 4.0 resides in the branch '3.9' and the branch '4.0' respectively.
Usage with JDK 9
Netty can be used in modular JDK9 applications as a collection of automatic modules. The module names follow the reverse-DNS style, and are derived from subproject names rather than root packages due to historical reasons. They are listed below:
io.netty.allio.netty.bufferio.netty.codecio.netty.codec.dnsio.netty.codec.haproxyio.netty.codec.httpio.netty.codec.http2io.netty.codec.memcacheio.netty.codec.mqttio.netty.codec.redisio.netty.codec.smtpio.netty.codec.socksio.netty.codec.stompio.netty.codec.xmlio.netty.commonio.netty.handlerio.netty.handler.proxyio.netty.resolverio.netty.resolver.dnsio.netty.transportio.netty.transport.epoll(nativeomitted - reserved keyword in Java)io.netty.transport.kqueue(nativeomitted - reserved keyword in Java)io.netty.transport.unix.common(nativeomitted - reserved keyword in Java)io.netty.transport.rxtxio.netty.transport.sctpio.netty.transport.udt
Automatic modules do not provide any means to declare dependencies, so you need to list each used module separately
in your module-info file.