转自: https://blog.csdn.net/houzhizhen/article/details/51372058
Records在Yarn中原代码中主要用于RPC通訊,如以下语句生成一个新应用程序的請求,GetNewApplicationRequest request =
Records.newRecord(GetNewApplicationRequest.class);
Records⾥的代码非常简单,调用newRecord时调用factory.newRecordInstance()方法,源代码如下:
public class Records { // The default record factory private static final RecordFactory factory = RecordFactoryProvider.getRecordFactory(null); public static <T> T newRecord(Class<T> cls) { return factory.newRecordInstance(cls); } }
fractory是RecordFactory类型的,是一个接口,只有一个方法,代码如下:
public interface RecordFactory { public <T> T newRecordInstance(Class<T> clazz); }
这个factory是RecordFactoryProvider.getRecordFactory(null)来初始化的。RecordFactoryProvider的源代码如下:
public class RecordFactoryProvider { private static Configuration defaultConf; static { defaultConf = new Configuration(); } private RecordFactoryProvider() { } public static RecordFactory getRecordFactory(Configuration conf) { if (conf == null) { //Assuming the default configuration has the correct factories set. //Users can specify a particular factory by providing a configuration. conf = defaultConf; } String recordFactoryClassName = conf.get( YarnConfiguration.IPC_RECORD_FACTORY_CLASS, YarnConfiguration.DEFAULT_IPC_RECORD_FACTORY_CLASS); return (RecordFactory) getFactoryClassInstance(recordFactoryClassName); } private static Object getFactoryClassInstance(String factoryClassName) { try { Class<?> clazz = Class.forName(factoryClassName); Method method = clazz.getMethod("get", null); method.setAccessible(true); return method.invoke(null, null); } catch (ClassNotFoundException e) { throw new YarnRuntimeException(e); } catch (NoSuchMethodException e) { throw new YarnRuntimeException(e); } catch (InvocationTargetException e) { throw new YarnRuntimeException(e); } catch (IllegalAccessException e) { throw new YarnRuntimeException(e); } } }
在方法⾥,由于传递的参数是null,所以conf = defaultConf,默认的DEFAULT_IPC_RECORD_FACTORY_CLASS 是 "org.apache.hadoop.yarn.factories.impl.pb.RecordFactoryPBImpl";调用getFactoryClassInstance("org.apache.hadoop.yarn.factories.impl.pb.RecordFactoryPBImpl")。
在getFactoryClassInstance方法⾥.,直接调用它的静态get方法,没有参数。RecordFactoryPBImpl的源代码如下: 1 public class RecordFactoryPBImpl implements Record 2
3 private static final String PB_IMPL_PACKAGE_SUFFIX = "impl.pb"; 4 private static final String PB_IMPL_CLASS_SUFFIX = "PBImpl"; 5 6 private static final RecordFactoryPBImpl self = new RecordFactoryPBImpl(); 7 private Configuration localConf = new Configuration(); 8 private ConcurrentMap<Class<?>, Constructor<?>> cache = new ConcurrentHashMap<Class<?>, Constructor<?>>(); 9 10 private RecordFactoryPBImpl() { 11 } 12 13 public static RecordFactory get() { 14 return self; 15 } 16 17 @SuppressWarnings("unchecked") 18 @Override 19 ....
}
RecordFactoryPBImpl是一个单例模式,get方法返回静态的final 变量 self.
在newRecordInstance(Class<T> clazz)方法⾥,首先判断cache是否能直接得到此类的构造器Constructor,如果得到,就直接调用constructor.newInstance();方法初始化一个对象,然后把此对象返回;如果缓冲器⾥没有,先调用getPBImplClassName(clazz)得到PBImpl的类实现,如getPBImplClassName(clazz);传递的是GetNewApplicationRequest,所在包是org.apache.hadoop.yarn.api.protocolrecords,按照规則,实现类是GetNewApplicationRequestPBImpl,所在包是org.apache.hadoop.yarn.api.protocolrecords.impl.pb, getPBImplClassName()方法返回的内容是org.apache.hadoop.yarn.api.protocolrecords.impl.pb.GetNewApplicationRequestPBImpl。
接着调用localConf.getClassByName("org.apache.hadoop.yarn.api.protocolrecords.impl.pb.GetNewApplicationRequestPBImpl")来返回class对象。然后得到它的constructor对象,放到cache⾥。
public <T> T newRecordInstance(Class<T> clazz) { Constructor<?> constructor = cache.get(clazz); if (constructor == null) { Class<?> pbClazz = null; try { pbClazz = localConf.getClassByName(getPBImplClassName(clazz)); } catch (ClassNotFoundException e) { throw new YarnRuntimeException("Failed to load class: [" + getPBImplClassName(clazz) + "]", e); } try { constructor = pbClazz.getConstructor(); constructor.setAccessible(true); cache.putIfAbsent(clazz, constructor); } catch (NoSuchMethodException e) { throw new YarnRuntimeException("Could not find 0 argument constructor", e); } } try { Object retObject = constructor.newInstance(); return (T)retObject; } catch (InvocationTargetException e) { throw new YarnRuntimeException(e); } catch (IllegalAccessException e) { throw new YarnRuntimeException(e); } catch (InstantiationException e) { throw new YarnRuntimeException(e); } } private String getPBImplClassName(Class<?> clazz) { String srcPackagePart = getPackageName(clazz); String srcClassName = getClassName(clazz); String destPackagePart = srcPackagePart + "." + PB_IMPL_PACKAGE_SUFFIX; String destClassPart = srcClassName + PB_IMPL_CLASS_SUFFIX; return destPackagePart + "." + destClassPart; } private String getClassName(Class<?> clazz) { String fqName = clazz.getName(); return (fqName.substring(fqName.lastIndexOf(".") + 1, fqName.length())); } private String getPackageName(Class<?> clazz) { return clazz.getPackage().getName(); }