hystrix源码之hystrix请求变量

Posted 2020-10-17 zwh1988

HystrixRequestContext

　　请求的上线文实现，内部定义了一个静态变量ThreadLocal,每个线程可以获取自己的HystrixRequestContext对象。一个请求往往由一个tomcat线程处理，所以在该tomcat线程中，HystrixRequestContext对象可以共享。

private static ThreadLocal<HystrixRequestContext> requestVariables = new ThreadLocal<HystrixRequestContext>();

　　HystrixRequestContext内部是一个ConcurrentHashMap存储请求变量。

ConcurrentHashMap<HystrixRequestVariableDefault<?>, HystrixRequestVariableDefault.LazyInitializer<?>> state = new ConcurrentHashMap<HystrixRequestVariableDefault<?>, HystrixRequestVariableDefault.LazyInitializer<?>>();

HystrixRequestVariableLifecycle->HystrixRequestVariable->HystrixRequestVariableDefault->HystrixLifecycleForwardingRequestVariable

　　HystrixRequestVariableLifecycle和HystrixRequestVariable定义了一个请求变量，这个请求变量对象的生命周期为在一个请求内。

　　HystrixRequestVariableDefault为默认实现类。内部他把变量值存储在HystrixRequestContext对象中。key为当前HystrixRequestVariableDefault对象，value为变量真正的值。

public T get() {
        if (HystrixRequestContext.getContextForCurrentThread() == null) {
            throw new IllegalStateException(HystrixRequestContext.class.getSimpleName() + ".initializeContext() must be called at the beginning of each request before RequestVariable functionality can be used.");
        }
        ConcurrentHashMap<HystrixRequestVariableDefault<?>, LazyInitializer<?>> variableMap = HystrixRequestContext.getContextForCurrentThread().state;

        // short-circuit the synchronized path below if we already have the value in the ConcurrentHashMap
        LazyInitializer<?> v = variableMap.get(this);
        if (v != null) {
            return (T) v.get();
        }
....

　　HystrixLifecycleForwardingRequestVariable只是一个封装对象，内部封装了一个HystrixRequestVariableLifecycle对象。

private final HystrixRequestVariableLifecycle<T> lifecycle;

HystrixRequestVariableHolder

　　定义了一个静态变量，存储所有的HystrixRequestVariable对象，全局共享。

private static ConcurrentHashMap<RVCacheKey, HystrixRequestVariable<?>> requestVariableInstance = new ConcurrentHashMap<RVCacheKey, HystrixRequestVariable<?>>();

　　RVCacheKey由两部分组成：当前HystrixRequestVariableHolder对象，指定HystrixConcurrencyStrategy对象。

public T get(HystrixConcurrencyStrategy concurrencyStrategy) { 
　　RVCacheKey key = new RVCacheKey(this, concurrencyStrategy);
　　...

　　如果没有已经存在的HystrixRequestVariable对象，通过HystrixConcurrencyStrategy新建一个。

...
if (rvInstance == null) {
            requestVariableInstance.putIfAbsent(key, concurrencyStrategy.getRequestVariable(lifeCycleMethods));
｝
...