|
How can it lock if you don't use InterlockedIncrement() for all cases? It can't.
The system has no way of knowing if you are changing the variable directly.
You have to use InterlockedIncrement() every place you increment the variable for it to work.
The way you've coded your thread, all 5 threads are going to increment the value regardless.
InterlockedIncrement() ensures the increment won't happen at the same time but it's still
going to happen as soon as another thread is done incrementing it.
Mark
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
|
|
|
|
|
1) do you mean : if first thread calls InterlockedIncrement(&i_Lock) first, then second thread calls i_Lock++;
the i_Lock++ still works?
2) what does "same time" mean?
do u mean: if InterlockedIncrement(&i_Lock); are called at "same time" by two threads, only one call works?
but, a PC has only one CPU, it can not change a value at "same time" by 2 threads in any way (++ or InterlockedIncrement).
|
|
|
|
|
includeh10 wrote: 1) do you mean : if first thread calls InterlockedIncrement(&i_Lock) first, then second thread calls i_Lock++;
the i_Lock++ still works?
Yes. All the threads incrementinging i_Lock should use InterlockedIncrement() to do so. That's
the only way the operation will be thread safe.
includeh10 wrote: 2) what does "same time" mean?
do u mean: if InterlockedIncrement(&i_Lock); are called at "same time" by two threads, only one call works?
but, a PC has only one CPU, it can not change a value at "same time" by 2 threads in any way (++ or InterlockedIncrement).
While it's true it won't occur at the "same time" on a single-processor machine, it's best to
assume that logically it can. You have no control over when the system is going to switch threads.
If the switch occurs right in the middle of a thread changing the variable and another thread
takes over and changes that variable then the first thread resumes but the variable has changed.
That can be bad.
In the simple case of incrementing a long, chances are pretty good these days that it will take
a single machine-code instruction to do the increment. Theoretically one wouldn't need
to use thread synchronization because the active thread isn't going to change in the middle
of a CPU instruction.
InterlockedIncrement() does more than just increment though. It also checks the result and
returns the result. Now imagine doing all those operations without thread synchronization:
1) i_Lock = 0
2) Thread A increments i_Lock - i_Lock now == 1
3) Thread B becomes the executing thread
4) Thread B increments i_Lock - i_Lock now == 2
5) Thread B gets the value of i_Lock (2)
6) Thread A becomes the executing thread
7) Thread A gets the value of i_Lock (2)
i_Lock should have been 1 in thread A but thread B changed it before thread A was finished.
Now do the same with proper synchronization:
1) i_Lock = 0
2) Thread A calls InterlockedIncrement() to increment i_Lock
3) Thread B becomes the executing thread
4) Thread B calls InterlockedIncrement() to increment i_Lock
5) Thread B is put into a waiting state (paused) until Thread A's call to InterlockedIncrement()
is completed
6) Thread A becomes the executing thread
7) Thread A's call to InterlockedIncrement() completes, returning 1 (i_Lock == 1)
8) Thread B becomes the executing thread
9) Thread B's call to InterlockedIncrement() is allowed to continue
10) Thread B's call to InterlockedIncrement() completes, returning 2 (i_Lock == 2)
That's the expected behavior - first-come, first-serve Make sense?
InterlockedIncrement() and InterlockedDeccrement() are often used for object reference count
variables. When an object's reference count is 0, often the object should be destroyed.
Imagine not synchronizing this process (as described above). Two threads try to decrement the
ref count on an object, but both think the ref count is 0 after they have done so. Both threads
try to destroy the object - one succeeds, one crashes.
Mark
"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder
|
|
|
|
|
Hai, i have an Access Control System which has a client server architecture, It supoports data tranfer to third part by a connectivity called SAGE. The manufacturer supplied all dlls and header files. but when i include these header files in my VC++ project to access Data from the system, i get Fatal Errors, cannot include the header files. What could be the problem. Can any one help please.. my mail id mahesh.mudackal@gmail.com
|
|
|
|
|
mahesh.mundackal wrote: but when i include these header files in my VC++ project to access Data from the system, i get Fatal Errors, cannot include the header files.
What errors?
Nobody can give you wiser advice than yourself. - Cicero
|
|
|
|
|
mahesh.mundackal wrote: i get Fatal Errors, cannot include the header files. What could be the problem.
Hint, hint. Linker is unable to find the header files. check your paths.
|
|
|
|
|
what errors? and can you show them.
|
|
|
|
|
Hi all,
I have created an SDI application and 3 dockable toolbars within them. But the problem is these toolbars are appearing in 3 different lines being left aligned. I want them to be in a single line unless the first line is filled.
Is there is any way to align the tool bar just after creation.
Anurag Gandhi.
|
|
|
|
|
Dear,
I want to insert an ActiveX control of DIO card in SDI Application. Previously I tried this in Dialog based application it worked. But when I inserted it in the SDI application. It Compiled with no errors but when I RUN it this is givig some error.
Plz any one of u have solution how to insert an ActiveX control in SDI plz send it.
Murali.S
|
|
|
|
|
Murali_mom wrote: this is givig some error.
Please wait until I search my telescope, so that I can look at your monitor to read those errors.
Nobody can give you wiser advice than yourself. - Cicero
|
|
|
|
|
Plz find some solution I need it badly
|
|
|
|
|
brahmma wrote: Please wait until I search my telescope, so that I can look at your monitor to read those errors.
Maybe dont need to telescope ,like advanced tools (did you see Ring I,II).
|
|
|
|
|
Can you more explain about errors?
|
|
|
|
|
I have a program,using thirdpart code.(there are some C codes in it)
It works when I debug it step by step,but it would crash if I run it weather in release or debug mode.
I found that there are some exceptions occur.But the most strange thing is that the exception cound not be catched using CException but only be catched if I use catch(...).
Someone would tell me why?
BEST REGARDS
|
|
|
|
|
You are probably stomping on memory that you do not own. Can you post relevant portion of the code where the crash occurs?
Nobody can give you wiser advice than yourself. - Cicero
|
|
|
|
|
OK,it very kind of you.
But if you give me your e-mail,that I can send the codes for you?
My E-mail is:kcynic@163.com
Thanks.
|
|
|
|
|
kcynic wrote: But if you give me your e-mail,that I can send the codes for you?
Please don't email me any code. Post the "relevant" code right here. By relevant, I mean the code where the crash occurs. That way, even if I can't figure out the problem, somebody else will! And the reply might be useful to someone who may search the forums for a similar problem in the future. That is the very reason behind having discussion forums.
PS: Edit your previous post to remove your email id from it. You are inviting spam by displaying your email ID on a public forum, which search engines will index.
Nobody can give you wiser advice than yourself. - Cicero
|
|
|
|
|
my codes is so simple,and the exception was occured in the thirdpart codes.
I don't think the error could be handled using such no sense codes.
my codes like this:
CMyODBC db;<br />
int rows=0;<br />
if(!db.ConnectDB("Test","sa",""))<br />
{<br />
AfxMessageBox("Opent the database failed!");<br />
return;<br />
}<br />
CString sql="SELECT * FROM [KB_USERS_ALL]";
CODBCSet set;<br />
<br />
db.PrepareSql(sql,set);<br />
try<br />
{<br />
db.FetchData();<br />
CString str;<br />
char* msg=set.m_coldata[0].value;<br />
}<br />
catch (...)
{<br />
AfxMessageBox("Exception");<br />
}<br />
<br />
try{ <br />
while(db.FetchData())<br />
{<br />
rows++;<br />
CString str;<br />
for(int i=0;i<set.GetCols();++i)<br />
str+=set.m_coldata[i].value;<br />
AfxMessageBox(str);<br />
}<br />
}catch(...)<br />
{<br />
AfxMessageBox("dfgdsg");<br />
}<br />
CString str;<br />
str.Format("there has %d records",rows);<br />
AfxMessageBox(str);<br />
try{<br />
}catch(...)<br />
{<br />
<br />
}
But thanks all the same.
Best regards to you.
|
|
|
|
|
You see, CException is the base class for all exceptions in MFC. I don't know an MFC class named CMyODBC. Check with your third party vendor if they have an exception handling class for their CMyODBC class.
Nobody can give you wiser advice than yourself. - Cicero
|
|
|
|
|
Looks like your third party C may be throwing but C doesn't use CException, that's a C++ class, so catch( CException ) won't work. You could try catch( std::exception ) in case it's throwing something derived from the standard library exception. Other than that I would try catch( char* ). Believe it or not this may be the only way to trap some C exceptions short of catch(...) which really doesn't let you find out what's wrong 
Nothing is exactly what it seems but everything with seems can be unpicked.
|
|
|
|
|
Matthew Faithfull wrote: Other than that I would try catch( char* ).
The Old Skool method 
Nobody can give you wiser advice than yourself. - Cicero
|
|
|
|
|
Yes,I know that you mean.The part C code CMyODBC only a general class using Win Database API,as you said,if there has some try block,it also doesn't throw CException.
Thanks.I would go steep into the code and find the error(because there is no try-catch block in it!)
|
|
|
|
|
|
Thanks,but I want to know why the codes didn't throw an exception when I trace it step by step,but only when I run it there would be some exception.
|
|
|
|
|
There's no obvious reason why you'd get exceptions only when you don't run step by step but there are two related likely causes.
Stepping through the code affects two things, speed and thread synchronisation. If multiple threads are involved then the code may work when single stepped but crash when run for real if data or resouce sharing between the threads is faulty.
If it's single threaded then all you really have left is speed and unless there's any io/comms external or interprocess communication going on then the difference would be hard to explain. Usually single stepping would only make the system work if the code being run is overrunning a buffer in another, flawed, process but doesn't fill the buffer as fast when single stepped so you don't see the bug.;)
The only way you're going to get to the bottom of this is to look at what the excpetion tells you and where it occurs. Find the exception code e.g. 0xC0000005 for Access Violation and make sure the debugger is set to always break on that exception. If the debugger is being cryptic you could always post what it says and someone may recognise it.
Nothing is exactly what it seems but everything with seems can be unpicked.
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
. Very nasty indeed. Good luck.