消息队列USER_MESSAGE_QUEUE

消息队列有7种：

• SendMessagesListHead
• PostedMessagesListHead
• HardwareMessagesListHead
• NotifyMessagesListHead

GetMessage函数会处理SendMessage,但是不会处理PostMessage,HardwareMessagesListHead
GetMeesage中，会把SendMessagesList中的所有消处处理完成后，再从其6个消息队列中拿出一个消息返回。
HardwareMessagesListHead中的消息，会由DispatchMessage来处理，即DispatchMessage函数会根据窗口句柄调用相关的窗口过程。因为一个进程的所有的窗口共享一个消息队列，但不同的窗口却有不同有消息处理函数。故这里是分发。分发使用窗口句柄HWND来标识。
通过窗口句柄，找到窗口对象，再进一步找到窗口回调函数，再调用它。

TranslateMessage:用于处理键盘的按键消息的。如将WM_KEYDOWN加工为WM_CHAR消息消息。如屏蔽TranslateMessage,系统将会只会收到WM_KEYDOWN消息，不会收到WM_CHAR消息。

typedef struct _USER_MESSAGE_QUEUE
{
  /* Owner of the message queue */
  struct _ETHREAD *Thread;
  /* Queue of messages sent to the queue. */
  LIST_ENTRY SentMessagesListHead;
  /* Queue of messages posted to the queue. */
  LIST_ENTRY PostedMessagesListHead;
  /* Queue of sent-message notifies for the queue. */
  LIST_ENTRY NotifyMessagesListHead;
  /* Queue for hardware messages for the queue. */
  LIST_ENTRY HardwareMessagesListHead;
  /* Lock for the hardware message list. */
  FAST_MUTEX HardwareLock;
  /* Lock for the queue. */
  FAST_MUTEX Lock;
  /* True if a WM_QUIT message is pending. */
  BOOLEAN QuitPosted;
  /* The quit exit code. */
  ULONG QuitExitCode;
  /* Set if there are new messages in any of the queues. */
  KEVENT NewMessages;  
  /* FIXME: Unknown. */
  ULONG QueueStatus;
  /* Current window with focus (ie. receives keyboard input) for this queue. */
  HWND FocusWindow;
  /* True if a window needs painting. */
  BOOLEAN PaintPosted;
  /* Count of paints pending. */
  ULONG PaintCount;
  /* Current active window for this queue. */
  HWND ActiveWindow;
  /* Current capture window for this queue. */
  HWND CaptureWindow;
  /* Current move/size window for this queue */
  HWND MoveSize;
  /* Current menu owner window for this queue */
  HWND MenuOwner;
  /* Identifes the menu state */
  BYTE MenuState;
  /* Caret information for this queue */
  PTHRDCARETINFO CaretInfo;

  /* Window hooks */
  PHOOKTABLE Hooks;

  /* queue state tracking */
  WORD WakeBits;
  WORD WakeMask;
  WORD ChangedBits;
  WORD ChangedMask;

  /* extra message information */
  LPARAM ExtraInfo;

} USER_MESSAGE_QUEUE, *PUSER_MESSAGE_QUEUE;