问WPF中的Control.InvokeRequired发生了什么？

EN

  if(this.InvokeRequired)
       this.Invoke(ProcessState);

  using MS.Internal.WindowsBase;
  using System;
  using System.ComponentModel;
  using System.Security;
  using System.Threading;

  namespace System.Windows.Threading
  {
     // Summary:
//     Provides services for managing the queue of work items for a thread.
public sealed class Dispatcher
{
    // Summary:
    //     Gets the System.Windows.Threading.Dispatcher for the thread currently executing
    //     and creates a new System.Windows.Threading.Dispatcher if one is not already
    //     associated with the thread.
    //
    // Returns:
    //     The dispatcher associated with the current thread.
    public static Dispatcher CurrentDispatcher { get; }
    //
    // Summary:
    //     Determines whether the System.Windows.Threading.Dispatcher has finished shutting
    //     down.
    //
    // Returns:
    //     true if the dispatcher has finished shutting down; otherwise, false.
    public bool HasShutdownFinished { get; }
    //
    // Summary:
    //     Determines whether the System.Windows.Threading.Dispatcher is shutting down.
    //
    // Returns:
    //     true if the System.Windows.Threading.Dispatcher has started shutting down;
    //     otherwise, false.
    public bool HasShutdownStarted { get; }
    //
    // Summary:
    //     Gets the collection of hooks that provide additional event information about
    //     the System.Windows.Threading.Dispatcher.
    //
    // Returns:
    //     The hooks associated with this System.Windows.Threading.Dispatcher.
    [EditorBrowsable(EditorBrowsableState.Advanced)]
    public DispatcherHooks Hooks { get; }
    //
    // Summary:
    //     Gets the thread this System.Windows.Threading.Dispatcher is associated with.
    //
    // Returns:
    //     The thread.
    public Thread Thread { get; }

    // Summary:
    //     Occurs when the System.Windows.Threading.Dispatcher finishes shutting down.
    public event EventHandler ShutdownFinished;
    //
    // Summary:
    //     Occurs when the System.Windows.Threading.Dispatcher begins to shut down.
    public event EventHandler ShutdownStarted;
    //
    // Summary:
    //     Occurs when a thread exception is thrown and uncaught during execution of
    //     a delegate by way of Overload:System.Windows.Threading.Dispatcher.Invoke
    //     or Overload:System.Windows.Threading.Dispatcher.BeginInvoke.
    public event DispatcherUnhandledExceptionEventHandler UnhandledException;
    //
    // Summary:
    //     Occurs when a thread exception is thrown and uncaught during execution of
    //     a delegate by way of Overload:System.Windows.Threading.Dispatcher.Invoke
    //     or Overload:System.Windows.Threading.Dispatcher.BeginInvoke when in the filter
    //     stage.
    public event DispatcherUnhandledExceptionFilterEventHandler UnhandledExceptionFilter;

    public DispatcherOperation BeginInvoke(Delegate method, params object[] args);
    //
    // Summary:
    //     Executes the specified delegate asynchronously at the specified priority
    //     on the thread the System.Windows.Threading.Dispatcher is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   method:
    //     The delegate to a method that takes no arguments, which is pushed onto the
    //     System.Windows.Threading.Dispatcher event queue.
    //
    // Returns:
    //     An object, which is returned immediately after Overload:System.Windows.Threading.Dispatcher.BeginInvoke
    //     is called, that can be used to interact with the delegate as it is pending
    //     execution in the event queue.
    //
    // Exceptions:
    //   System.ArgumentNullException:
    //     method is null.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid System.Windows.Threading.DispatcherPriority.
    [EditorBrowsable(EditorBrowsableState.Never)]
    [Browsable(false)]
    public DispatcherOperation BeginInvoke(DispatcherPriority priority, Delegate method);
    public DispatcherOperation BeginInvoke(Delegate method, DispatcherPriority priority, params object[] args);
    //
    // Summary:
    //     Executes the specified delegate asynchronously at the specified priority
    //     and with the specified argument on the thread the System.Windows.Threading.Dispatcher
    //     is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   method:
    //     A delegate to a method that takes one argument, which is pushed onto the
    //     System.Windows.Threading.Dispatcher event queue.
    //
    //   arg:
    //     The object to pass as an argument to the specified method.
    //
    // Returns:
    //     An object, which is returned immediately after Overload:System.Windows.Threading.Dispatcher.BeginInvoke
    //     is called, that can be used to interact with the delegate as it is pending
    //     execution in the event queue.
    //
    // Exceptions:
    //   System.ArgumentNullException:
    //     method is null.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid System.Windows.Threading.DispatcherPriority.
    [EditorBrowsable(EditorBrowsableState.Never)]
    [Browsable(false)]
    public DispatcherOperation BeginInvoke(DispatcherPriority priority, Delegate method, object arg);
    //
    // Summary:
    //     Executes the specified delegate asynchronously at the specified priority
    //     and with the specified array of arguments on the thread the System.Windows.Threading.Dispatcher
    //     is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   method:
    //     A delegate to a method that takes multiple arguments, which is pushed onto
    //     the System.Windows.Threading.Dispatcher event queue.
    //
    //   arg:
    //     The object to pass as an argument to the specified method.
    //
    //   args:
    //     An array of objects to pass as arguments to the specified method.
    //
    // Returns:
    //     An object, which is returned immediately after Overload:System.Windows.Threading.Dispatcher.BeginInvoke
    //     is called, that can be used to interact with the delegate as it is pending
    //     execution in the System.Windows.Threading.Dispatcher queue.
    //
    // Exceptions:
    //   System.ArgumentNullException:
    //     method is null.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     System.Windows.Threading.DispatcherPriority is not a valid priority.
    [Browsable(false)]
    [EditorBrowsable(EditorBrowsableState.Never)]
    public DispatcherOperation BeginInvoke(DispatcherPriority priority, Delegate method, object arg, params object[] args);
    //
    // Summary:
    //     Initiates shutdown of the System.Windows.Threading.Dispatcher asynchronously.
    //
    // Parameters:
    //   priority:
    //     The priority at which to begin shutting down the dispatcher.
    [SecurityCritical]
    public void BeginInvokeShutdown(DispatcherPriority priority);
    //
    // Summary:
    //     Determines whether the calling thread is the thread associated with this
    //     System.Windows.Threading.Dispatcher.
    //
    // Returns:
    //     true if the calling thread is the thread associated with this System.Windows.Threading.Dispatcher;
    //     otherwise, false.
    [EditorBrowsable(EditorBrowsableState.Never)]
    public bool CheckAccess();
    //
    // Summary:
    //     Disables processing of the System.Windows.Threading.Dispatcher queue.
    //
    // Returns:
    //     A structure used to re-enable dispatcher processing.
    public DispatcherProcessingDisabled DisableProcessing();
    //
    // Summary:
    //     Requests that all frames exit, including nested frames.
    [SecurityCritical]
    public static void ExitAllFrames();
    //
    // Summary:
    //     Gets the System.Windows.Threading.Dispatcher for the specified thread.
    //
    // Parameters:
    //   thread:
    //     The thread to obtain the System.Windows.Threading.Dispatcher from.
    //
    // Returns:
    //     The dispatcher for thread.
    public static Dispatcher FromThread(Thread thread);
    public object Invoke(Delegate method, params object[] args);
    //
    // Summary:
    //     Executes the specified delegate synchronously at the specified priority on
    //     the thread on which the System.Windows.Threading.Dispatcher is associated
    //     with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   method:
    //     A delegate to a method that takes no arguments, which is pushed onto the
    //     System.Windows.Threading.Dispatcher event queue.
    //
    // Returns:
    //     The return value from the delegate being invoked or null if the delegate
    //     has no return value.
    //
    // Exceptions:
    //   System.ArgumentException:
    //     priority is equal to System.Windows.Threading.DispatcherPriority.Inactive.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid priority.
    //
    //   System.ArgumentNullException:
    //     method is null.
    [Browsable(false)]
    [EditorBrowsable(EditorBrowsableState.Never)]
    public object Invoke(DispatcherPriority priority, Delegate method);
    public object Invoke(Delegate method, DispatcherPriority priority, params object[] args);
    public object Invoke(Delegate method, TimeSpan timeout, params object[] args);
    //
    // Summary:
    //     Executes the specified delegate at the specified priority with the specified
    //     argument synchronously on the thread the System.Windows.Threading.Dispatcher
    //     is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   method:
    //     A delegate to a method that takes one argument, which is pushed onto the
    //     System.Windows.Threading.Dispatcher event queue.
    //
    //   arg:
    //     An object to pass as an argument to the given method.
    //
    // Returns:
    //     The return value from the delegate being invoked or null if the delegate
    //     has no return value.
    //
    // Exceptions:
    //   System.ArgumentException:
    //     priority is equal to System.Windows.Threading.DispatcherPriority.Inactive.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid priority.
    //
    //   System.ArgumentNullException:
    //     method is null.
    [EditorBrowsable(EditorBrowsableState.Never)]
    [Browsable(false)]
    public object Invoke(DispatcherPriority priority, Delegate method, object arg);
    //
    // Summary:
    //     Executes the specified delegate synchronously at the specified priority and
    //     with the specified time-out value on the thread the System.Windows.Threading.Dispatcher
    //     was created.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   timeout:
    //     The maximum time to wait for the operation to finish.
    //
    //   method:
    //     The delegate to a method that takes no arguments, which is pushed onto the
    //     System.Windows.Threading.Dispatcher event queue.
    //
    // Returns:
    //     The return value from the delegate being invoked or null if the delegate
    //     has no return value.
    [Browsable(false)]
    [EditorBrowsable(EditorBrowsableState.Never)]
    public object Invoke(DispatcherPriority priority, TimeSpan timeout, Delegate method);
    public object Invoke(Delegate method, TimeSpan timeout, DispatcherPriority priority, params object[] args);
    //
    // Summary:
    //     Executes the specified delegate at the specified priority with the specified
    //     arguments synchronously on the thread the System.Windows.Threading.Dispatcher
    //     is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   method:
    //     A delegate to a method that takes multiple arguments, which is pushed onto
    //     the System.Windows.Threading.Dispatcher event queue.
    //
    //   arg:
    //     An object to pass as an argument to the given method.
    //
    //   args:
    //     An array of objects to pass as arguments to the given method.
    //
    // Returns:
    //     The return value from the delegate being invoked or null if the delegate
    //     has no return value.
    //
    // Exceptions:
    //   System.ArgumentException:
    //     priority is equal to System.Windows.Threading.DispatcherPriority.Inactive.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid priority.
    //
    //   System.ArgumentNullException:
    //     method is null.
    [EditorBrowsable(EditorBrowsableState.Never)]
    [Browsable(false)]
    public object Invoke(DispatcherPriority priority, Delegate method, object arg, params object[] args);
    //
    // Summary:
    //     Executes the specified delegate at the specified priority with the specified
    //     argument synchronously on the thread the System.Windows.Threading.Dispatcher
    //     is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   timeout:
    //     The maximum time to wait for the operation to finish.
    //
    //   method:
    //     A delegate to a method that takes multiple arguments, which is pushed onto
    //     the System.Windows.Threading.Dispatcher event queue.
    //
    //   arg:
    //     An object to pass as an argument to the given method. This can be null if
    //     no arguments are needed.
    //
    // Returns:
    //     The return value from the delegate being invoked or null if the delegate
    //     has no return value.
    //
    // Exceptions:
    //   System.ArgumentException:
    //     priority is equal to System.Windows.Threading.DispatcherPriority.Inactive.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid priority.
    //
    //   System.ArgumentNullException:
    //     method is null.
    [EditorBrowsable(EditorBrowsableState.Never)]
    [Browsable(false)]
    public object Invoke(DispatcherPriority priority, TimeSpan timeout, Delegate method, object arg);
    //
    // Summary:
    //     Executes the specified delegate at the specified priority with the specified
    //     arguments synchronously on the thread the System.Windows.Threading.Dispatcher
    //     is associated with.
    //
    // Parameters:
    //   priority:
    //     The priority, relative to the other pending operations in the System.Windows.Threading.Dispatcher
    //     event queue, the specified method is invoked.
    //
    //   timeout:
    //     The maximum time to wait for the operation to finish.
    //
    //   method:
    //     A delegate to a method that takes multiple arguments, which is pushed onto
    //     the System.Windows.Threading.Dispatcher event queue.
    //
    //   arg:
    //     An object to pass as an argument to the specified method.
    //
    //   args:
    //     An array of objects to pass as arguments to the specified method.
    //
    // Returns:
    //     The return value from the delegate being invoked or null if the delegate
    //     has no return value.
    //
    // Exceptions:
    //   System.ArgumentException:
    //     priority is equal to System.Windows.Threading.DispatcherPriority.Inactive.
    //
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid System.Windows.Threading.DispatcherPriority.
    //
    //   System.ArgumentNullException:
    //     method is null.
    [Browsable(false)]
    [EditorBrowsable(EditorBrowsableState.Never)]
    public object Invoke(DispatcherPriority priority, TimeSpan timeout, Delegate method, object arg, params object[] args);
    //
    // Summary:
    //     Initiates the shutdown process of the System.Windows.Threading.Dispatcher
    //     synchronously.
    [SecurityCritical]
    public void InvokeShutdown();
    //
    // Summary:
    //     Enters an execute loop.
    //
    // Parameters:
    //   frame:
    //     The frame for the dispatcher to process.
    //
    // Exceptions:
    //   System.ArgumentNullException:
    //     frame is null.
    //
    //   System.InvalidOperationException:
    //     System.Windows.Threading.Dispatcher.HasShutdownFinished is true -or- frame
    //     is running on a different System.Windows.Threading.Dispatcher.  -or- Dispatcher
    //     processing has been disabled.
    [SecurityCritical]
    public static void PushFrame(DispatcherFrame frame);
    //
    // Summary:
    //     Pushes the main execution frame on the event queue of the System.Windows.Threading.Dispatcher.
    [SecurityCritical]
    public static void Run();
    //
    // Summary:
    //     Determines whether the specified System.Windows.Threading.DispatcherPriority
    //     is a valid priority.
    //
    // Parameters:
    //   priority:
    //     The priority to check.
    //
    //   parameterName:
    //     A string that will be returned by the exception that occurs if the priority
    //     is invalid.
    //
    // Exceptions:
    //   System.ComponentModel.InvalidEnumArgumentException:
    //     priority is not a valid System.Windows.Threading.DispatcherPriority.
    public static void ValidatePriority(DispatcherPriority priority, string parameterName);
    //
    // Summary:
    //     Determines whether the calling thread has access to this System.Windows.Threading.Dispatcher.
    //
    // Exceptions:
    //   System.InvalidOperationException:
    //     The calling thread does not have access to this System.Windows.Threading.Dispatcher.
    [EditorBrowsable(EditorBrowsableState.Never)]
    public void VerifyAccess();
}