Threads are sometimes called lightweight processes, program execution flow is the smallest unit. A standard thread from the thread ID, the current instruction pointer (PC), registers and stack composed of a collection. In addition, the threads a process Zhong of an entity only is system independent of the basic unit of scheduling and distribution, the thread does not personally own system of Zi Yuan, Zhi has a 1:00 in the running essential of resources, but it may belong to a process with the Qi Ta threads sharing all the resources owned by the process. A thread can create and undo another thread, the same process can be concurrent execution between multiple threads. As the threads between the constraints, resulting in the operation of the thread showing a discontinuity. Thread also has in place, blocking and running three basic states. Thread is a single program control flow sequence. In a single program run multiple threads to complete different tasks, known as multi-threading.