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Once again we are back to the question of how to best terminate a thread. A "regular" thread is easy. A simple boolean variable set to false could terminate a while loop and allow the thread to exit. What happens when a thread is blocked, though? For example, if we had a TCP/IP server and called
m_pSocket->Accept(m_conSocket);
That call will block the thread until a connection is made. What is the best way then to terminate the thread without having to terminate the main thread?
Thanks.
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Well you could use TerminateThread() but that's not recommended. For the TCP/IP server example another solution would be to use a function like select(), with a small time out, to check for incomming connections on the socket and only the call accept() or read() or any other blocking calls. This way the thread will never be blocked for a long time. You could then use a boolean variable to stop it and perform clean up.
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Your asking for trouble even thinking of calling TerminateThread. Here's an example program which shows the kind of thing that can go wrong:
------------------------------------------
#include <windows.h>
CRITICAL_SECTION g_cs;
void ShowMessageBox()
{
EnterCriticalSection(&g_cs);
MessageBox(NULL, "Hello", "ShowMessageBox", MB_OK);
LeaveCriticalSection(&g_cs);
}
DWORD WINAPI ThreadProc(LPVOID lpParameter)
{
ShowMessageBox();
return 0;
}
int main(int argc, char* argv[])
{
InitializeCriticalSection(&g_cs);
// Start thread.
DWORD ThreadID;
HANDLE hThread = CreateThread(NULL, 0, &ThreadProc, 0, 0, &ThreadID);
// Wait for one second then kill the thread.
// It still holds the CRITICAL_SECTION!!!
Sleep(1000);
TerminateThread(hThread, 0);
// We've killed the "ShowMessageBox" API, permanently, calling it now
// causes this thread to dead lock!
ShowMessageBox();
DeleteCriticalSection(&g_cs);
return 0;
}
------------------------------------------
In this program calling TerminateThread permanently breaks ShowMessageBox because we killed the thread when it still held a lock. This is the worst kind of bug as it's very hard to reproduce as it's sensitive to timing. If you're calling Win32 functions many of them will briefly hold locks, if you terminate a thread while it is hold such a lock you're screwed.
Moral: Don't call TerminateThread. There are exceptions but very few.
Steve
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masnu wrote: A simple boolean variable set to false could terminate a while loop and allow the thread to exit.
Be sure you have not instructed the compiler to ignore testing the boolean with each iteration of the loop. Use of volatile will help here.
"The greatest good you can do for another is not just to share your riches but to reveal to him his own." - Benjamin Disraeli
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Hi,
I have got a query related to 'Unicode to MBCS conversions'.
First of all a brief information about project. I have got 2 projects, 1 is Unicode (Non-ISAPI) and other Non - Unicode (ISAPI). I need to pass the values from project 1 to project 2. Then this is going to be sent to ISAPI which in turn display the value in the browser through ASP page. I am using pseudo resources in which some characters are visible correctly while some are not. This output in the browser is through ISAPI calls written in project 2. My aim is to see the output in the browser correctly.
I m getting Output as follows:
?eí?í†íàlí$e
????àr†er ?à$ reí?í†íàlí$ed ??.
?lí?? here †? re†?r? †? †?e ????àr†er ???e ?à?e.
Following code snippet is written in project 1:
In order to convert Unicode strings to MBCS following conversion is done.
char* mbcsBuff = (char*) malloc ((strMessage.GetLength() + 1) * sizeof(_TCHAR));
wcstombs( mbcsBuff, strMessage, (strMessage.GetLength() + 1) * sizeof(_TCHAR));
mbcsBuff needs to be passed to project 2 in the form of BSTR.
Project 2: BSTR string from project 1 is then converted to CString here and passed to ISAPI call (StartContent(), EndContent()) and sent to browser.
Now how do i see the output correctly?
I have tried my level best to put up the problem clearly, even then feel free to ask me more details if needed. Urgent support is needed. Thank you in advance.
Nishith
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Take a look at the function WideCharToMultiByte. This converts strings from unicode to MBCS.
Deus caritas est
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Is the Unicode string coming out correctly? Also, which code page do you want to use to convert the Unicode string to MBCS? Also BSTRs are Unicode strings prefixed by length, so why not create a BSTR from the output of project 1 from the Unicode string? You can then pass this BSTR to project 2 and then convert to MBCS.
Deus caritas est
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Is the Unicode string coming out correctly? Also, which code page do you want to use to convert the Unicode string to MBCS? Also BSTRs are Unicode strings prefixed by length, so why not create a BSTR from the output of project 1 from the Unicode string? You can then pass this BSTR to project 2 and then convert to MBCS.
Deus caritas est
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Hi Andy,
Yes Unicode string is correct in project 1. I have used code page as 1200 for conversions. Is it possible to convert BSTR string into MBCS in a Non-Unicode project? Since project 2 is having ISAPI calls where exactly i need to pass on this MBCS string, i tried doing the same but the result was the same (No change in the outout).
Also i have tried WideCharToMultiByte() but the result is the same.
One more point project 2 cannot be made as Unicode project since ISAPI calls are used to pass on the strings to the browser.
Can you throw some more light on this issue? Thank you for your time.
Nishith
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meet2nishith wrote: Yes Unicode string is correct in project 1. I have used code page as 1200 for conversions. Is it possible to convert BSTR string into MBCS in a Non-Unicode project?
try _bstr_t class it expose char* for non Unicode projects
"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow
cheers,
Alok Gupta
VC Forum Q&A :- I/ IV
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I'm having a little trouble getting this code to work. The documentation on MSDN could suck a beach ball through a garden hose!
midiOutGetVolume((HMIDIOUT)MIDI_MAPPER,&OldMidiVol);
From my understanding 'MIDI_MAPPER' is supposed to find the correct device. Yet the above function returns MMSYSERR_NOTSUPPORTED. If I replace the MIDI_MAPPER with '0', it works as it should do.
This is totally confusing me. Does the 'MMSYSERR_NOTSUPPORTED' error mean the function is not supported or that 'MIDI_MAPPER' is not supported? And why if a change the value does it work?
I want this code to be portable and I'm guessing that if I simply replace 'MIDI_MAPPER' with a '0' would cause problems as this may not be true on all machines.
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midiOutGetVolume() accepts a handle to an open MIDI device or a device ID. MIDI_MAPPER</code (which does not have the value 0, rather 0xffffffff) is neither - it is a flag passed to <code>midiOutOpen() or midiOutGetDevCaps(). This flag is not supported by midiOutGetVolume(). You'll have to open the MIDI mapper with midiOutOpen() first.
Ryan "Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"
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Hi,
Can anybody point to a links which tells
1. Building a static library in MSVC 6.0
2. Linking the same with application MSVC 6.0
As i am facing problems.
I built the static library with settings Multi threaded dll (both for release and debug).
I am trying to link with my application. It is not working at all. lot of mismatchings.
Regards, Eswari
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Hi all,
Ya it's somewhat confusion question.
Here I want embed java applet in the VC++ to control the browser, browser (.html) page is also generated by VC++ coding.
If I want to the VC++ app by the browser, then what type tool I need to embed with VC++ ?
Thankx,
Awating your reply,
- Ramesh
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Re-modified,
Ya it's somewhat confusion question.
Here I want to embed java applet in the VC++ to control the browser, browser (.html) page is also generated by VC++ coding.
If I want to control the VC++ app from the browser shown (.html) page, then what type of tool will be required to embed with VC++ ?
Thankx,
- Ramesh
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hi, i m working on a project where i want to a html file in SDI view
sourabh jain
patni computers system
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For this, you can use a CHtmlView instead of the standard CEditView, or use a CFormView (I think) and add one HTML controls available on Code Project to the view.
~RaGE();
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I have a dual monitor on my system and it is very convenient to have different windows on separate monitors. On the bottom of my screen I have Find Results 1 and Find Results 2 as separated tabs (I have a picture but can't figure out how to paste it here).
If I pin both of them, they appear one of top of the other.
When debugging a program in run mode, I also have separated groups of tabs. In the debug mode if I pin both of them, they appear left and right of one another and I can adjust them to be on separate monitors.
I would very much like to be able to do the same left-right ordering in edit mode, but I can't figure out what controls it. For Find Results 1 and 2 this is especially convenient to be able to arrange on separate monitors, but as is they are above and below one another, completely wasting the space on the second monitor.
Any suggestions would be greatly appreciated.
Ilan
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Hi
I am using Visual Studio 2005. I have developed my project in VC++ which is a dialog based MFC application.
Here on the Button Click event of one dialog i need to get the value inserted in one edit box. for that I have declared variable also and i use GetWindowTextA() functions for that and it throw assertions. Showsing NULL value in hWnd...
I don't know why this happens........any idea? The same code works fine in Visual Studio 6.0
My Code looks like this :
=========================
void CPswdWnd::OnBnClickedButton1()
{
// TODO: Add your control notification handler code here
char sCurPswd[512]="";
m_Pswd.GetWindowTextA(sCurPswd,strlen(sCurPswd)); //Here it give assertion
}
My Variables are declared by righ clicking the Editbox and then "Add Variables" and then i have made the variable as "Control".
Any idea?
Thankx in advance
Mahesh
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void CPswdWnd::OnBnClickedButton1()
{
char sCurPswd[512]="";
m_Pswd.GetWindowText(sCurPswd,strlen(sCurPswd));
}
Without "A" at the end. The compiler decides then which one fits best.
~RaGE();
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Since the buffer the O.P. allocated is a char buffer, they need to be using it with the ANSI version of the function. If their app is a UNICODE build, GetWindowText(...) will resolve to GetWindowTextW(...), and will not accept the char buffer.
Identifiers like GetWindowText that are #defined to different functions (the A or W versions) depending on the build type should only be expected to work correctly under different build types when using TCHAR as the character type.
Peace!
-=- James
If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
DeleteFXPFiles & CheckFavorites (Please rate this post!)
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It is likely ASSERTing because the you are passing the return from strlen(...) as the length of the buffer. These are two different things.
You should be calling the function like: m_Pswd.GetWindowTextA(sCurPswd,512).
Peace!
--- Modified at 10:34 Tuesday 14th February, 2006
Actually, the second parameter is the max number of characters to copy into the buffer. This is important, because it does not mean the size of the buffer. That is why using sizeof(...) as was also suggested would be incorrect in a UNICODE build.
-=- James
If you think it costs a lot to do it right, just wait until you find out how much it costs to do it wrong!
Avoid driving a vehicle taller than you and remember that Professional Driver on Closed Course does not mean your Dumb Ass on a Public Road!
DeleteFXPFiles & CheckFavorites (Please rate this post!)
-- modified at 10:34 Tuesday 14th February, 2006
Actually, the second parameter is the max number of characters to copy into the buffer. This is important, because it does not mean the size of the buffer. That is why using sizeof(...) as was also suggested would be incorrect in a UNICODE build.
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Amarelia wrote: m_Pswd.GetWindowTextA(sCurPswd,strlen(sCurPswd)); //Here it give assertion
Use sizeof(sCurPswd)*sizeof(TCHAR) instead of strlen(sCurPswd).
"The greatest good you can do for another is not just to share your riches but to reveal to him his own." - Benjamin Disraeli
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