inheritableThreadLocal
能满足上下文之间的数据传递
前提是在父类线程中创建子类线程;
参见源码如下:
Thread类有两个属性
ThreadLocal.ThreadLocalMap threadLocals = null; ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
我们在进行new Thread()会调用下方init方法:
该方法会获取父线程的inheritableThreadLocals并赋值到当前线程
private void init(ThreadGroup g, Runnable target, String name, long stackSize, AccessControlContext acc, boolean inheritThreadLocals) { if (name == null) { throw new NullPointerException("name cannot be null"); } this.name = name; Thread parent = currentThread(); SecurityManager security = System.getSecurityManager(); if (g == null) { /* Determine if it's an applet or not */ /* If there is a security manager, ask the security manager what to do. */ if (security != null) { g = security.getThreadGroup(); } /* If the security doesn't have a strong opinion of the matter use the parent thread group. */ if (g == null) { g = parent.getThreadGroup(); } } /* checkAccess regardless of whether or not threadgroup is explicitly passed in. */ g.checkAccess(); /* * Do we have the required permissions? */ if (security != null) { if (isCCLOverridden(getClass())) { security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION); } } g.addUnstarted(); this.group = g; this.daemon = parent.isDaemon(); this.priority = parent.getPriority(); if (security == null || isCCLOverridden(parent.getClass())) this.contextClassLoader = parent.getContextClassLoader(); else this.contextClassLoader = parent.contextClassLoader; this.inheritedAccessControlContext = acc != null ? acc : AccessController.getContext(); this.target = target; setPriority(priority); if (inheritThreadLocals && parent.inheritableThreadLocals != null) this.inheritableThreadLocals = ThreadLocal.createInheritedMap(parent.inheritableThreadLocals); /* Stash the specified stack size in case the VM cares */ this.stackSize = stackSize; /* Set thread ID */ tid = nextThreadID(); }
其中springcloud的hystrix采用线程池进行资源隔离
此时可以采用HystrixConcurrencyStrategy进行上下文传递，为什么不采用inheritableThreadLocal进行上下文传递
这里就要说到inheritableThreadLocal传递的特性，创建线程
hystrix采用的是线程池技术，所以不是每次请求都一定会创建线程，如果是获取线程资源池的线程而不是创建线程
则父线程的属性并不会被传递给子线程
