[Quiz] What will happen if SendMessage to self?

This is an interesting thing (what i never thought of yet...) and I wonder how you people think it will happen.

We normally won't sendmessage to ourself, but what if we do that?

Here are the sample example:

Code:

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LRESULT CDlgExeDlg::DefWindowProc(UINT message, WPARAM wParam, LPARAM lParam)
{
        // TODO: Add your specialized code here and/or call the base class
        switch (message)
        {
        case WM_MYTEST:
                {
                        if (! SendMessage(WM_MYTEST)) {
                                ASSERT(0);
                        };
                       
                        int i = 0;

                }
.....

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Because SendMessage is a synchronous function, so THEORETICALLY it will casue an infinite loop!

But is this true?

How do you people think?

Quote:

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Originally Posted by myron

...Because SendMessage is a synchronous function, so THEORETICALLY it will casue an infinite loop!

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Yes it will, and then - stack overlow...
Did you try?

m. but actually (usiang VC6)

it just runs!
(After a certain number of stack-record repetition...)
A very interesting things...

Says, what if we repalce WM_MYTEST with WM_CREATE?

The dialog/app still shows up!

What a magic.

Quote:

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Originally Posted by myron

We normally won't sendmessage to ourself, but what if we do that?

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We normally don't send messages recursively to ourself (i.e. send WM_MYMESSAGE inside a WM_MYMESSAGE handler), but other than that its very normal to send messages to ourself.

Well, there is a trcik here.
Sendmessage is synchronous function, so "theoretically" this will cause system hang out... since the sendmessage won't return back... (in single thread condition of course)

Quote:

---

...
case WM_MYTEST:
{
if (! SendMessage(WM_SOMEOTHERMSG)) {
ASSERT(0);
};
...

---

it's the first sign of madness

Quote:

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Originally Posted by myron

Well, there is a trcik here.
Sendmessage is synchronous function, so "theoretically" this will cause system hang out... since the sendmessage won't return back... (in single thread condition of course)

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Unless I'm mistaken it won't necesarily hang...first execution is in the case WM_MYTEST code, then when you call SendMessage(WM_SOMETHINGELSE), execution goes to the WM_SOMETHINGELSE handler. When that handler completes, execution returns to the WM_MYTEST handler, after the SendMessage call.

Now, if we're talking about Windows messages, not user defined messages, it may or may not cause problems, depending on the message & what Windows does with it.