Several questions about Windows Message Queue

1. Do all messages start with WM?

No, and

Prefix	Message category	Documentation
ABM and ABN	Application desktop Toolbar	Shell messages and notifications
ACM and ACN	Animation Control	Animation control messages and animation control notifications
BCM, BCN, BM, and BN	Button Control	Button Control Messages and button control notifications
CB and CBN	ComboBox control	ComboBox control messages and ComboBox control specifications
Cbem and cben	Comboboxex Control	Comboboxex messages and comboboxex notifications
CCM	General Control	Control Messages
CDM	Common Dialog Box	Common Dialog Box messages
DFM	Default context menu	Shell messages and notifications
DL	Drag list box	Drag list box configurations
DM	Default push button control	Dialog Box messages
DTM and dtn	Date and Time picker Control	Date and Time picker messages and date and time picker notifications
Em and EN	Edit Control	Edit Control Messages, Edit Control notifications, rich edit messages, and rich edit notifications
HDM AND HDN	Header Control	Header control messages and header control notifications
Hkm	Hot Key Control	Hot Key Control Messages
IPM and IPN	IP address control	IP address messages and IP address communications
LB and LBN	List box Control	List box messages and list box notifications
Lm	Syslink Control	Syslink Control Messages
LVM and LVN	List View Control	List View Messages and List View notifications
MCM and MCN	Month calendar Control	Month calendar messages and month calendar notifications
PBM	Progress bar	Progress bar messages
PGM and PGN	Pager Control	Pager control messages and pager control notifications
PSM and pSN	Property sheet	Property sheet messages and property sheet notifications
Rb and rBN	Rebar Control	Rebar control messages and rebar control notifications
SB and SBN	Status Bar window	Status Bar messages and status bar notifications
SBM	Scroll bar Control	Scroll bar messages
SMC	Shell menu	Shell messages and notifications
STM and STN	Static Control	Static Control Messages and static control configurations
TB and TBN	Toolbar	Toolbar Control Messages and Toolbar Control notifications
TBM and trbn	Trackbar Control	Trackbar control messages and trackbar control notifications
TCM and TCN	Tab Control	Tab control messages and Tab control notifications
TDM and TDN	Task Dialog	Task dialog messages and task dialog notifications
TTM and ttn	Tooltip Control	Tooltip control messages and tooltip control notifications
TVM and TVN	Tree-View Control	Tree View Messages and Tree View notifications
UDM and UDN	Up-down control	Up-down messages and up-down notifications

 

2. range I of message numbers and custom messages

Message-identifier values are used as follows:

• The system reserves message-identifier values in the range 0x0000 through 0x03ff (the valueWm_user-1) for system-defined messages. applications cannot use these values for private messages.
• Values in the range 0x0400 (the valueWm_user) Through 0x7fff are available for message identifiers for private window classes.
• If your application is marked version 4.0, you can use message-identifier values in the range 0x8000 (Wm_app) Through 0 xbfff for private messages.
• The system returns a message identifier in the range 0xc000 through 0 xFFFF when an application calltheRegisterwindowmessageFunction to register a message. the message identifier returned by this function is guaranteed to be unique throughout the system. use of this function prevents conflicts that can arise if other applications use the same message identifier for different purposes.

That is: 0x0000 to 0x03ff (WM_USER-1) is system retained and applications cannot use

0x0400 (wm_user) to 0x07ff, which can be used in the private window class, that is, internal application

After windows95 and nt3.5 (there is a windows3.1 and nt3.1 in front, I am lucky to spend a few days, ah, I am also old enough) 0x0800 (wm_app) to 0xbff will also be used by the program.

0xc000 to 0xffff are global custom messages that can be used between unused applications. For such a message, you must callRegisterwindowmessageThe system allocates a number. Therefore, when the program runs twice, registering the same message may have different numbers.

 

3. Are message queues owned by windows, threads, and processes?

The system maintains a single system message queue and one thread-specific message queue for each GUI thread.

The system has a system queue, and each GUI thread has a queue of its own.

 

4. When will a Message Queue be created?

To avoid the overhead of creating a message queue for non-Gui threads, all threads are created initially without a message queue. the system creates a thread-specific message queue only when the thread makes its first call to one of the specific user functions; no GUI function callresult in the creation of a message queue.

No message queue is generated for all wired threads. When a thread calls a specific function for the first time, a message queue is created.

System messages (such as keyboard, mouse, wm_quit, and wm_paint) are first sent to the system message queue. Then, the system extracts messages from the queue one by one to see the window to which the message is sent, put the message in the queue of the Creation thread in this window.

The system creates a thread's message queue when the thread makes its first call
To one of the user or GDI functions.

 

5. Are all messages in the message queue?

No. Divided into queued message and none queued message. The former includes the mouse, keyboard event, wm_paint, wm_quit, wm_timer, and so on. The latter includes wm_active and wm_setfocus. None queued message is sent through sendmessage. The sending of these messages directly calls the processing function of the corresponding window (the statement is not rigorous, and only the window of the same thread can be called directly; otherwise, wait for the target window to complete the call. Cross-thread transmission involves the issue of callback alling)

Notification message,SendpolicymessageThe sent message is not placed in the message queue. The behavior of this function is the same as that of sendmessage when the target window belongs to the sending thread. It is returned only after the message is processed. When the target window is in another thread, the behavior is the same as that of postmessage, and the message is returned after the message processing is complete.

 

6. What is the size of a message queue?

There is a limit of 10,000 posted messages per message queue. this limit shoshould be sufficiently large. if your application exceeds the limit, it shoshould be redesigned to avoid consuming so far system resources. to adjust this limit, modify the following registry key.

 

HKEY_LOCAL_MACHINE   SOFTWARE      Microsoft         Windows NT            CurrentVersion               Windows                  USERPostMessageLimit

The default value is 10000.

Refer:

1. http://msdn.microsoft.com/en-us/library/ms644927(v=vs.85).aspx

2. msdn description of attatchthreadinput

3. Refer to the msdn documentation for related APIs in 1.