218 lines
11 KiB
Plaintext
218 lines
11 KiB
Plaintext
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USER MODULE
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===========
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USER implements windowing and messaging subsystems. It also
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contains code for common controls and for other miscellaneous
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stuff (rectangles, clipboard, WNet, etc). Wine USER code is
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located in windows/, controls/, and misc/ directories.
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1. Windowing subsystem
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Windows are arranged into parent/child hierarchy with one
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common ancestor for all windows (desktop window). Each window
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structure contains a pointer to the immediate ancestor (parent
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window if WS_CHILD style bit is set), a pointer to the sibling
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(returned by GetWindow(..., GW_NEXT)), a pointer to the owner
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window (set only for popup window if it was created with valid
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hwndParent parameter), and a pointer to the first child
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window (GetWindow(.., GW_CHILD)). All popup and non-child windows
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are therefore placed in the first level of this hierarchy and their
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ancestor link (wnd->parent) points to the desktop window.
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Desktop window - root window
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| \ '-.
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| \ '-.
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popup -> wnd1 -> wnd2 - top level windows
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| \ '-. '-.
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| \ '-. '-.
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child1 child2 -> child3 child4 - child windows
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Horizontal arrows denote sibling relationship, vertical lines
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- ancestor/child. To summarize, all windows with the same immediate
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ancestor are sibling windows, all windows which do not have desktop
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as their immediate ancestor are child windows. Popup windows behave
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as topmost top-level windows unless they are owned. In this case the
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only requirement is that they must precede their owners in the top-level
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sibling list (they are not topmost). Child windows are confined to the
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client area of their parent windows (client area is where window gets
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to do its own drawing, non-client area consists of caption, menu, borders,
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intrinsic scrollbars, and minimize/maximize/close buttons).
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Another fairly important concept is "z-order". It is derived from
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the ancestor/child hierarchy and is used to determine "above/below"
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relationship. For instance, in the example above, z-order is
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child1->popup->child2->child3->wnd1->child4->wnd2->desktop. Current
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active window ("foreground window" in Win32) is moved to the front
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of z-order unless its top-level ancestor owns popup windows.
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All these issues are dealt with (or supposed to be) in
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windows/winpos.c
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Wine specifics: in default and managed mode each top-level window
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gets its own X counterpart with desktop window being basically a
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fake stub. In desktop mode, however, only desktop window has X
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window associated with it.
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2. Messaging subsystem
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Each Windows task/thread has its own message queue - this is where
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it gets messages from. Messages can be generated on the fly
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(WM_PAINT, WM_NCPAINT, WM_TIMER), they can be created by the system
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(hardware messages), they can be posted by other tasks/threads
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(PostMessage), or they can be sent by other tasks/threads (SendMessage).
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Message priority:
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First the system looks for sent messages, then for posted messages,
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then for hardware messages, then it checks if the queue has the
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"dirty window" bit set, and, finally, it checks for expired
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timers. See windows/message.c.
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From all these different types of messages, only posted messages go
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directly into the private message queue. System messages (even in
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Win95) are first collected in the system message queue and then
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they either sit there until Get/PeekMessage gets to process them
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or, as in Win95, if system queue is getting clobbered, a special
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thread ("raw input thread") assigns them to the private
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queues. Sent messages are queued separately and the sender sleeps
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until it gets a reply. Special messages are generated on the fly
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depending on the window/queue state. If the window update region is
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not empty, the system sets the QS_PAINT bit in the owning queue and
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eventually this window receives a WM_PAINT message (WM_NCPAINT too
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if the update region intersects with the non-client area). A timer
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event is raised when one of the queue timers expire. Depending on
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the timer parameters DispatchMessage either calls the callback
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function or the window procedure. If there are no messages pending
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the task/thread sleeps until messages appear.
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There are several tricky moments (open for discussion) -
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a) System message order has to be honored and messages should be
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processed within correct task/thread context. Therefore when
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Get/PeekMessage encounters unassigned system message and this
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message appears not to be for the current task/thread it should
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either skip it (or get rid of it by moving it into the private
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message queue of the target task/thread - Win95, AFAIK) and
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look further or roll back and then yield until this message
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gets processed when system switches to the correct context
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(Win16). In the first case we lose correct message ordering, in
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the second case we have the infamous synchronous system message
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queue. Here is a post to one of the OS/2 newsgroup I found to
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be relevant:
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" Here's the problem in a nutshell, and there is no good solution.
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Every possible solution creates a different problem.
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With a windowing system, events can go to many different windows.
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Most are sent by applications or by the OS when things relating to
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that window happen (like repainting, timers, etc.)
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Mouse input events go to the window you click on (unless some window
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captures the mouse).
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So far, no problem. Whenever an event happens, you put a message on
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the target window's message queue. Every process has a message
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queue. If the process queue fills up, the messages back up onto the
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system queue.
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This is the first cause of apps hanging the GUI. If an app doesn't
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handle messages and they back up into the system queue, other apps
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can't get any more messages. The reason is that the next message in
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line can't go anywhere, and the system won't skip over it.
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This can be fixed by making apps have bigger private message queues.
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The SIQ fix does this. PMQSIZE does this for systems without the SIQ
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fix. Applications can also request large queues on their own.
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Another source of the problem, however, happens when you include
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keyboard events. When you press a key, there's no easy way to know
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what window the keystroke message should be delivered to.
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Most windowing systems use a concept known as "focus". The window
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with focus gets all incoming keyboard messages. Focus can be changed
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from window to window by apps or by users clicking on winodws.
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This is the second source of the problem. Suppose window A has focus.
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You click on window B and start typing before the window gets focus.
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Where should the keystrokes go? On the one hand, they should go to A
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until the focus actually changes to B. On the other hand, you
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probably want the keystrokes to go to B, since you clicked there
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first.
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OS/2's solution is that when a focus-changing event happens (like
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clicking on a window), OS/2 holds all messages in the system queue
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until the focus change actually happens. This way, subsequent
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keystrokes go to the window you clicked on, even if it takes a while
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for that window to get focus.
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The downside is that if the window takes a real long time to get focus
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(maybe it's not handling events, or maybe the window losing focus
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isn't handling events), everything backs up in the system queue and
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the system appears hung.
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There are a few solutions to this problem.
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One is to make focus policy asynchronous. That is, focus changing has
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absolutely nothing to do with the keyboard. If you click on a window
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and start typing before the focus actually changes, the keystrokes go
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to the first window until focus changes, then they go to the second.
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This is what X-windows does.
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Another is what NT does. When focus changes, keyboard events are held
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in the system message queue, but other events are allowed through.
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This is "asynchronous" because the messages in the system queue are
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delivered to the application queues in a different order from that
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with which they were posted. If a bad app won't handle the "lose
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focus" message, it's of no consequence - the app receiving focus will
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get its "gain focus" message, and the keystrokes will go to it.
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The NT solution also takes care of the application queue filling up
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problem. Since the system delivers messages asynchronously, messages
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waiting in the system queue will just sit there and the rest of the
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messages will be delivered to their apps.
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The OS/2 SIQ solution is this: When a focus-changing event happens,
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in addition to blocking further messages from the application queues,
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a timer is started. When the timer goes off, if the focus change has
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not yet happened, the bad app has its focus taken away and all
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messages targetted at that window are skipped. When the bad app
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finally handles the focus change message, OS/2 will detect this and
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stop skipping its messages.
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As for the pros and cons:
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The X-windows solution is probably the easiest. The problem is that
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users generally don't like having to wait for the focus to change
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before they start typing. On many occasions, you can type and the
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characters end up in the wrong window because something (usually heavy
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system load) is preventing the focus change from happening in a timely
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manner.
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The NT solution seems pretty nice, but making the system message queue
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asynchronous can cause similar problems to the X-windows problem.
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Since messages can be delivered out of order, programs must not assume
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that two messages posted in a particular order will be delivered in
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that same order. This can break legacy apps, but since Win32 always
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had an asynchronous queue, it is fair to simply tell app designers
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"don't do that". It's harder to tell app designers something like
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that on OS/2 - they'll complain "you changed the rules and our apps
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are breaking."
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The OS/2 solution's problem is that nothing happens until you try to
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change window focus, and then wait for the timeout. Until then, the
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bad app is not detected and nothing is done." (by David Charlap)
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b) Intertask/interthread SendMessage. The system has to inform the
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target queue about the forthcoming message, then it has to
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carry out the context switch and wait until the result is
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available. In Win16 it is done by putting necessary parameters
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into the queue structure and do a DirectedYield() call.
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However, in Win32 there could be several messages pending sent
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by preemptively executing threads, and in this case SendMessage
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has to build some sort of message queue for sent
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messages. Another issue is what to do with messages sent to the
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sender when it is blocked inside its own SendMessage. At this
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point Wine does not address any of these problems.
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