Most objects in WPF derive from DispatcherObject,which provides the
basic constructs for dealing with concurrency and threading. WPF is
based on a messaging system implemented by the dispatcher. This works
much like the familiar Win32 message pump; in fact,the WPF dispatcher
uses User32 messages for performing cross thread calls.
There are really two core concepts to understand when discussing
concurrency in WPF – the dispatcher and thread affinity.
During the design phase of WPF,the goal was to move to a single
thread of execution,but a non-thread “affinitized” model. Thread
affinity happens when a component uses the identity of the executing
thread to store some type of state. The most common form of this is to
use the thread local store (TLS) to store state. Thread affinity
requires that each logical thread of execution be owned by only one
physical thread in the operating system,which can become memory
intensive. In the end,WPF’s threading model was kept in sync with the
existing User32 threading model of single threaded execution with
thread affinity. The primary reason for this was interoperability –
systems like OLE 2.0,the clipboard,and Internet Explorer all require
single thread affinity (STA) execution.
Given that you have objects with STA threading,you need a way to
communicate between threads,and validate that you are on the correct
thread. Herein lies the role of the dispatcher. The dispatcher is a
basic message dispatching system,with multiple prioritized queues.
Examples of messages include raw input notifications (mouse moved),
framework functions (layout),or user commands (execute this method).
By deriving from DispatcherObject,you create a CLR object that has
STA behavior,and will be given a pointer to a dispatcher at creation
time.
就个人而言,我更喜欢WPF的单线程模型,而不必使用锁定和线程同步技术. Dispatcher可用于将消息传递到different priority levels的主UI线程,该线程负责大多数小型后台进程,如果您需要任何繁重的处理,那么您仍然可以为其创建自己的后台线程.
