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Adaptive 这个应该是 Dubbo SPI 里最玄妙的东西了，一开始没懂，自适应扩展点加载，dubbo://123.123.123.123:1234/com.nicksxs.demo.service.HelloWorldService?anyhost=true&application=demo&default.loadbalance=random&default.service.filter=LoggerFilter&dubbo=2.5.3&interface=com.nicksxs.demo.service.HelloWorldService&logger=slf4j&methods=method1,method2,method3,method4&pid=4292&retries=0&side=provider&threadpool=fixed&threads=200&timeout=2000×tamp=1590647155886threadpool = fixed，说明线程池使用的是 fixed 对应的实现，也就是下图的这个
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譬如我们在引用一个服务时，在ReferenceConfig 中的
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private static final Protocol refprotocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
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就获取了自适应拓展，
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 public T getAdaptiveExtension () Object instance = cachedAdaptiveInstance.get(); if (instance == null ) { if (createAdaptiveInstanceError == null ) { synchronized (cachedAdaptiveInstance) { instance = cachedAdaptiveInstance.get(); if (instance == null ) { try { instance = createAdaptiveExtension(); cachedAdaptiveInstance.set(instance); } catch (Throwable t) { createAdaptiveInstanceError = t; throw new IllegalStateException("fail to create adaptive instance: " + t.toString(), t); } } } } else { throw new IllegalStateException("fail to create adaptive instance: " + createAdaptiveInstanceError.toString(), createAdaptiveInstanceError); } } return (T) instance; }
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这里也使用了 DCL，来锁cachedAdaptiveInstance，当缓存中没有时就去创建自适应拓展
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 private T createAdaptiveExtension () try { return injectExtension((T) getAdaptiveExtensionClass().newInstance()); } catch (Exception e) { throw new IllegalStateException("Can not create adaptive extension " + type + ", cause: " + e.getMessage(), e); } } private Class<?> getAdaptiveExtensionClass() { getExtensionClasses(); if (cachedAdaptiveClass != null ) { return cachedAdaptiveClass; } return cachedAdaptiveClass = createAdaptiveExtensionClass(); } private Class<?> createAdaptiveExtensionClass() { String code = createAdaptiveExtensionClassCode(); ClassLoader classLoader = findClassLoader(); com.alibaba.dubbo.common.compiler.Compiler compiler = ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.common.compiler.Compiler.class ).getAdaptiveExtension () ; return compiler.compile(code, classLoader); }
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生成的代码像这样
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 package com.alibaba.dubbo.rpc;import com.alibaba.dubbo.common.extension.ExtensionLoader;public class Protocol $Adaptive implements com .alibaba .dubbo .rpc .Protocol public void destroy () throw new UnsupportedOperationException( "method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!" ); } public int getDefaultPort () throw new UnsupportedOperationException( "method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!" ); } public com.alibaba.dubbo.rpc.Exporter export ( com.alibaba.dubbo.rpc.Invoker arg0) throws com.alibaba.dubbo.rpc.RpcException { if (arg0 == null ) { throw new IllegalArgumentException( "com.alibaba.dubbo.rpc.Invoker argument == null" ); } if (arg0.getUrl() == null ) { throw new IllegalArgumentException( "com.alibaba.dubbo.rpc.Invoker argument getUrl() == null" ); } com.alibaba.dubbo.common.URL url = arg0.getUrl(); String extName = ((url.getProtocol() == null ) ? "dubbo" : url.getProtocol()); if (extName == null ) { throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])" ); } com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class ) .getExtension (extName ) ; return extension.export(arg0); } public com.alibaba.dubbo.rpc.Invoker refer (java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1) throws com.alibaba.dubbo.rpc.RpcException { if (arg1 == null ) { throw new IllegalArgumentException("url == null" ); } com.alibaba.dubbo.common.URL url = arg1; String extName = ((url.getProtocol() == null ) ? "dubbo" : url.getProtocol()); if (extName == null ) { throw new IllegalStateException( "Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url(" + url.toString() + ") use keys([protocol])" ); } com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class ) .getExtension (extName ) ; return extension.refer(arg0, arg1); } }
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