C / C++ / MFC

Re: Difference between Critical Sections over Mutex objects

13-Sep-11 0:13

Thanks for the comment.

Yeah your comment give me a some kind of idea. But then, what is the advantage use of a mutex to control multiple process and multiple Critical Sections to control multiple process?

I appreciate your help all the time...
CodingLover Smile | :)

ShilpiP13-Sep-11 1:05

ShilpiP

13-Sep-11 1:05

Mutex and Critical Section are used for synchronization.Both are almost same except that Critical Section is used within a same process area, where mutex is used in different process area.

I will explain you with simple example:
Suppose in your project, You are using one array and two threads are running simultaneously. First thread add data in an array and other display that data on screen.

Scenario 1: Without Critical section
There is a schedular program in OS that give time slot to every process and threads that are running. It is so frequently done that we feel that all threads are running simultaneous.Suppose time slot given to both thread is equal. If thread one is running it can add only 40 data and than time slot is given to other thread and it display 50 data. Now for some data some garbage data is displayed.
If threads uses the same resourse and we must synchronize the thread. In this case we use CS.Process area of both the thread is same, So it is fast.

Scenario 2: Suppose we use printer machine to print some data. If two person request at a time and if no synchronization process is used than it gives to garbage data. At this time one process have to wait to complete the process of second. This time the process or thread are from different process area. So we use mutexes. The process area of process is different, So it is slow.

I think this example will clear your doubt. Smile | :)

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Re: Difference between Critical Sections over Mutex objects

CodingLover13-Sep-11 1:22

Re: Difference between Critical Sections over Mutex objects

13-Sep-11 1:22

Thanks for the comment.

Pretty much clear what you are saying now.

However lets consider the scenario 1 for a minute. As you explain we can use CS to control the two threads and guaranteed that data adding or reading take place at a time. But the order of the execution is not guaranteed. That's clear. At the same time we can mutex on that too. At that point what's the advantage of each.

Hope I am clear with my this question.

I appreciate your help all the time...
CodingLover Smile | :)

ShilpiP13-Sep-11 2:17

ShilpiP

13-Sep-11 2:17

My suggestion is you must read about the synchronization of thread.
There are four types of synchronization
1) Critical section
2) Mutex
3) Event
4) Semaphore
Every synchronization object is used to meet different requirement and as per our requirement we have to choose which synchronization object is used in our application.

Re: Difference between Critical Sections over Mutex objects

CodingLover13-Sep-11 17:39

Re: Difference between Critical Sections over Mutex objects

13-Sep-11 17:39

SP 24 wrote:
My suggestion is you must read about the synchronization of thread.

Of course, I myself have to do that. Smile | :)

BTW do you know any good online resources?

Regarding my previous comment, do you have any thoughts of it? If so I would like to know.

I appreciate your help all the time...
CodingLover Smile | :)

ShilpiP13-Sep-11 18:39

ShilpiP

13-Sep-11 18:39

Google will help you Smile | :)

MSDN

a) MultiThreading[^]

b) Multithreading: When to Use the Synchronization Classes[^]

c) Informit[^]

Re: Difference between Critical Sections over Mutex objects

CodingLover13-Sep-11 21:21

Problem using IAccessible2

13-Sep-11 21:21

Thanks a lot. I'll have a look at them. Smile | :)

I appreciate your help all the time...
CodingLover Smile | :)

kartikdasani12-Sep-11 2:17

kartikdasani

12-Sep-11 2:17

I have been trying to write automation code for Mozilla Firefox and need to use the IAccessible2 interface in my code.
The problem is that I keep getting the error : No such interface supported. I have registered the IAccessible2Proxy.dll. But still get the error.

web browser control difficulty

doug2512-Sep-11 1:28

12-Sep-11 1:28

Hello, I'm trying to display a web page inside my own window.

I found a c++ example by chris becke on the net which is huge. I ported the code into my application but I can only get the web page to display when I run the project in visual c++.

Is there a more bare bone example that displays a web page inside a window ? or why does my program only work when I run it from visual c++ ?

I'm not of a great state of intelligence to understand all the com code needed to display a web page but with a little help I think I might understand..

thanks,

CPallini12-Sep-11 2:16

CPallini

12-Sep-11 2:16

If you are using MFC then you may have a look at "Using MFC to Host a WebBrowser Control"[^] at MSDN.

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doug2513-Sep-11 2:50

13-Sep-11 2:50

Thanks, but i'm not using MFC

krmed12-Sep-11 3:56

krmed

12-Sep-11 3:56

When you run an application from inside Visual Studio, the working directory is the directory containing the project files (.vcxproj, .sln). However when you run outside of VS, the working directory is the one containing the .exe file.

So if you are opening an html file with just a file name (e.g. open "MyTest.html") then that file must exist in the working directory. You should use full path names to avoid this problem. (You can use GetModuleFileName to find out the directory containing your exe).

Hope that helps.

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doug2513-Sep-11 2:59

13-Sep-11 2:59

I understand this, I have been using the full path and file name.

I need to convert the string to a BSTR, I'm assuming i'm doing it correctly because as I say, the program works but only shows a web page when I run it from visual studio.
here's how:

C++

 char url[MAX_PATH];
 // _getcwd(url, MAX_PATH);
  GetModuleFileName(InstanceHandle, url, MAX_PATH);
  std::string file = url;
  file = file.substr(0, file.find_last_of("\\"));
  file += "\\Help.html";
  //file = "Help.html";

// show that the path is correct
  MessageBox(NULL, file.c_str(), NULL, NULL);

   OLECHAR* oleChar = NULL;
    oleChar = (OLECHAR*)calloc(file.length(), sizeof(OLECHAR));
    MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, file.c_str(), -1, oleChar, sizeof(WCHAR)*file.length());

  vURL.bstrVal = SysAllocString(oleChar);

doug2513-Sep-11 11:18

Member function pionters in C++

13-Sep-11 11:18

I've got the program to work Smile | :)

! after some modifications. still not sure what the problem was but I think it had something to do with structure declarations I'd placed in a header file..

Erudite_Eric12-Sep-11 0:30

12-Sep-11 0:30

So I use a lot of function pointers in C, and wanted to add one to a C++ class (MFC).

So I start off with a typedef in my class:

typedef ULONG (MyClass::*MyFunc)(PULONG, PVOID);

The call back:

ULONG MyFunc(PULONG, PVOID);

Another func that takes the callback as a parameter:

ULONG SomeFunc(PULONG, MyFunc, PVOID);

I then write the implementaiton of SomeFunc:
ULONG MyClass::SomeFunc(PULONG pVal, MyFunc pProc, PVOID pOpt)
{
...
}

To call the callback from inside MyClass::SomeFunc() I had to use this syntax:

ULONG ret = (this->*pProc)(&x, NULL);

I couldn't just call (*pProc)(&x, NULL); I had to add the 'this->'.

What a crappy syntax. You dont have to call other member funcs with a 'this->' so why is it required for function pointers?

--edit--

Perhaps it would look better as: (*this.*pProc)(&x, NULL); Smile | :)

Nah, thats WAY to much direction...

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Nothing to say.

image processing toolkits | batch image processing

C^hris L^osinger12-Sep-11 1:52

C^hris L^osinger

12-Sep-11 1:52

Fat__Eric wrote:
What a crappy syntax. You dont have to call other member funcs with a 'this->' so why is it required for function pointers?

probably because whoever designed C++ was kind enough to mandate an implicit this-> for member fns, because calling member fns is a very common situation, but didn't bother for member fn ptrs, because that's much less common.

you can just make a macro for that ugly syntax

Erudite_Eric12-Sep-11 2:09

12-Sep-11 2:09

Chris Losinger wrote:
probably because whoever designed C++ was kind enough to mandate an implicit
this-> for member fns

You dont need to specify 'this->' when calling member funcs, you just call them by name. Thats the point I am making.

Chris Losinger wrote:
fn ptrs, because that's much less common.

Used a lot in C though. A heck of a lot. Surprises me they werent better catered for in C++.

Chris Losinger wrote:
you can just make a macro for that ugly syntax

Yeah, it sure is a pigs arse. Smile | :)

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Nothing to say.

CPallini12-Sep-11 2:13

CPallini

12-Sep-11 2:13

Fat__Eric wrote:
Used a lot in C though. A heck of a lot. Surprises me they werent better catered for in C++

Possibly because C++ doesn't encourage C-style programming.

Erudite_Eric12-Sep-11 2:33

12-Sep-11 2:33

Yet there are a lot of functions in the Win32 API that use call backs. Smile | :)

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Nothing to say.

MicroVirus12-Sep-11 3:08

MicroVirus

12-Sep-11 3:08

The Windows API is more C than it is C++.

Erudite_Eric12-Sep-11 3:09

12-Sep-11 3:09

Are you suggesting that C++ was designed to be incompatible with the win 32 API? Smile | :)

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Nothing to say.

MicroVirus12-Sep-11 8:29

MicroVirus

12-Sep-11 8:29

Well... since all my C++ Win32 programs seem to work, I guess that can't be it, right? Poke tongue | ;-P