C / C++ / MFC

HOW WHAT29-Apr-07 4:33

29-Apr-07 4:33

volatile bool Sentinel = true;<br />
<br />
unsigned ThreadFunc1( void* pArguments ) {<br />
   while (Sentinel){;}<br />
      <br />
......<br />
   return 0;<br />
} <br />
<br />
unsigned  ThreadFunc2( void* pArguments ) {<br />
   Sentinel = false; // exit critical section<br />
   return 0;<br />
}

--------------------------------------------
Ago, i think if a thread readning a address, and other thread write this address, that will be conflict. But why above not happen error and crash.

you say "You are doing (at least) 2 things", but InterlockedExchange only 1 operation, how to use it.

underside is my some code, can u help me see is it safe?

1.

volatile LONG g_Value = -1;<br />
<br />
LONG Read()<br />
{<br />
......<br />
    return InterlockedExchange(&g_Value, g_Value);<br />
}<br />
<br />
VOID Write(LONG NewValue)<br />
{<br />
......<br />
    return InterlockedExchange(&g_Value, NewValue);<br />
}<br />
<br />
VOID Thread1()<br />
{<br />
    if (Read >= 0)<br />
    {<br />
        Write(-1);<br />
        <br />
        for (INT i = 0; i < 10; i++)<br />
        {<br />
            Write(i);<br />
            if (RunThread3() == error)<br />
            {<br />
                Write(-1);<br />
            }<br />
        }<br />
    }<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
    // code same with Thread1 function<br />
}

-----------------------------------------------------

2.

volatile LONG g_nIndex = -1;<br />
<br />
VOID Thread1()<br />
{<br />
    InterlockedExchange(&g_nIndex, 1);<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
    do<br />
    {<br />
    }<br />
    while (InterlockedExchange(&g_nIndex, g_nIndex) < -1);<br />
}<br />
<br />
VOID Thread3()<br />
{<br />
    INT nIndex = GetIndex();<br />
    InterlockedExchange(&g_nIndex, nIndex);<br />
}

-----------------------------------------------------

3.

volatile LONG g_nData1 = 0L;<br />
<br />
VOID Thread1()<br />
{<br />
    if (InterlockedExchange(&g_nData1, g_nData1) == 0)<br />
    {<br />
        InterlockedExchangePointer(&g_nData1, 1);<br />
    }<br />
<br />
.................<br />
<br />
    if (InterlockedExchangePointer(&g_nData1, g_nData1) == 1)<br />
    {<br />
        InterlockedExchangePointer(&g_nData1, 0L);<br />
    }<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
    // code same with Thread1<br />
}

-------------------------------------------------------

4.

volatile LONG g_bIsLock = 0L;<br />
<br />
VOID Thread1()<br />
{<br />
    if (InterlockedExchange(&g_bIsLock, g_bIsLock) == 1)<br />
    {<br />
        InterlockedExchange(&g_bIsLock, 0L);<br />
    }<br />
    else<br />
    {<br />
        InterlockedExchange(&g_bIsLock, 1);<br />
    }<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
    InterlockedExchange(&g_bIsLock, g_bIsLock);<br />
}<br />
<br />
VOID Thread3()<br />
{<br />
    if (InterlockedExchange(&g_bIsLock, g_bIsLock))<br />
    {<br />
        <br />
    }<br />
}

Thanks very much for your help.

cmk29-Apr-07 9:13

cmk

29-Apr-07 9:13

Your code does not make sense.

Do not use:
if( InterlockedExchange() ) {
InterlockedExchange();
}
This is bad, you are doing 2 things (test and set) in 2 instructions.

Instead use:
while( InterlockedCompareExchange(&lock, 1, 0) ) {
// lock was == 0, now == 1, 'this' thread set lock = 1
}
This is better, you are doing 2 things in 1 instruction.

...cmk

Save the whales - collect the whole set

HOW WHAT29-Apr-07 20:05

29-Apr-07 20:05

Yes, my code not make sense, it only write example for my question.

Is nether code right now? Which Interlocked functions unneed?

1.

volatile LONG g_Value = -1;<br />
<br />
LONG Read()<br />
{<br />
	// return g_Value;<br />
	return InterlockedExchange(&g_Value, g_Value);<br />
}<br />
<br />
VOID Write(LONG NewValue)<br />
{<br />
	// g_Value = NewValue;<br />
	InterlockedExchange(&g_Value, NewValue);<br />
}<br />
<br />
VOID Thread1()<br />
{<br />
	if (Read() >= 0)<br />
	{<br />
		Write(-1);<br />
<br />
		for (INT i = 0; i < 10; i++)<br />
		{<br />
			......<br />
			Write(i);<br />
<br />
			if (RunThread2() == error)<br />
			{<br />
				......<br />
				Write(-1);<br />
			}<br />
		}<br />
	}<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
	// code same with Thread1 function<br />
}

-----------------------------------------------------

2.

volatile LONG g_nIndex = -1;<br />
<br />
VOID Thread1()<br />
{<br />
	// g_nIndex = 1;<br />
	InterlockedExchange(&g_nIndex, 1);<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
	do<br />
	{<br />
		......<br />
	}<br />
	// while (g_nIndex < -1);<br />
	while (InterlockedExchange(&g_nIndex, g_nIndex) < -1);<br />
}<br />
<br />
VOID Thread3()<br />
{<br />
	INT nIndex = GetIndex();<br />
<br />
	// g_nIndex = nIndex;<br />
	InterlockedExchange(&g_nIndex, nIndex);<br />
}

-----------------------------------------------------

3.

volatile LONG g_nData1 = 0L;<br />
<br />
VOID Thread1()<br />
{<br />
	// if (0L == g_nData1) g_nData = 1;<br />
	InterlockedCompareExchange(g_nData1, 1, 0L);<br />
<br />
	.................<br />
<br />
	// if (1 == g_nData1) g_nData = 0L;<br />
	InterlockedCompareExchange(g_nData1, 0, 1);<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
	// code same with Thread1<br />
}

-------------------------------------------------------

4.

volatile LONG g_bIsLock = 0L;<br />
<br />
VOID Thread1()<br />
{<br />
	// if (1 == g_bIsLock) g_bIsLock = 0;<br />
	InterlockedCompareExchange(g_nData1, 0L, 1);<br />
}<br />
<br />
VOID Thread2()<br />
{<br />
	// if (0 == g_bIsLock)<br />
	if (InterlockedExchange(&g_bIsLock, g_bIsLock) == 0L)<br />
	{<br />
		......<br />
	}<br />
}<br />
<br />
VOID Thread3()<br />
{<br />
	// if (1 == g_bIsLock)<br />
	if (InterlockedExchange(&g_bIsLock, g_bIsLock) == 1)<br />
	{<br />
		......<br />
	}<br />
}

---------------------------------------------

And can u tell me why nether MSDN example unuseInterlocked functions, but it can work right and have not resource conflict( a thread read value, the other one write value)

volatile bool Sentinel = true;<br />
<br />
unsigned ThreadFunc1( void* pArguments ) {<br />
	while (Sentinel){;}<br />
<br />
	......<br />
	return 0;<br />
} <br />
<br />
unsigned ThreadFunc2( void* pArguments ) {<br />
	Sentinel = false; // exit critical section<br />
	return 0;<br />
}

HOW WHAT28-Apr-07 22:48

28-Apr-07 22:48

http://msdn2.microsoft.com/en-us/library/ms684122.aspx[^][^]

Unclear why those code run not happen error, if
if "volatile bool Sentinel = true;" -> "bool Sentinel = true;" , have some different?

cmk29-Apr-07 0:01

cmk

29-Apr-07 0:01

HOW WHAT wrote:
Unclear why those code run not happen error, if
if "volatile bool Sentinel = true;" -> "bool Sentinel = true;" , have some different?

http://msdn2.microsoft.com/en-us/library/12a04hfd(VS.80).aspx[^]

volatile is important.
It tells the compiler that the value could change any time.
e.g.

void  Thread1( void )
{
    while( Sentinal ) {
        ...
    }
}
void  Thread2( void )
{
    ...
    Sentinal = false;
    (wait for Thread1 to finish)
    ...
}

If Sentinal is NOT volatile then Thread1 may cache the value of Sentinal when the Thread1 starts and never reload it becuase it is not used anywhere else in Thread1 (it optimizes the load out). In the example above this could cause Thread2 to wait forever becuase Thread1 never exits.

If Sentinal IS volatile then Thread1 reloads the value in each iteration of the while loop.
Therefore when Thread2 changes Sentinal Thread1 will see the change.

...cmk

Save the whales - collect the whole set

HOW WHAT29-Apr-07 2:49

29-Apr-07 2:49

May i understand that it's real-time and not optimize code of all about this value?

how to make very large numbers

cmk29-Apr-07 9:04

cmk

29-Apr-07 9:04

I do not understand what you are saying.

...cmk

Save the whales - collect the whole set

g3RC4n27-Apr-07 15:43

g3RC4n

27-Apr-07 15:43

is there a libary or something where i can get numbers which have like 50 digits without truncation, for a program for find prime numbers etc???

also why i'm here

***************************************************
***************************************************

i'm trying to use the .clear() with vectors but they never work

Code:

#include <iostream>
#include <vector>

using namespace std;
int main()
{
vectornumbers;

int createindex = 100;

while(createindex)
{
numbers.push_back(createindex);
createindex--;
}
cout << numbers[20] << endl;
numbers.clear();
cout << numbers[20] << endl;

system("PAUSE");
return 0;
}

what am i doing wrong?

thanks i'n advanced

David Crow27-Apr-07 17:02

David Crow

27-Apr-07 17:02

g3RC4n wrote:
what am i doing wrong?

Not using <pre> tags for one thing. The other thing is that your code snippet (i.e., adding to a vector) has nothing to do with your question (i.e., large numbers, primes).

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Rajesh R Subramanian27-Apr-07 19:31

Rajesh R Subramanian

27-Apr-07 19:31

DavidCrow wrote:
Not using <pre> tags for one thing.

Laugh | :laugh:

g3RC4n27-Apr-07 23:11

g3RC4n

27-Apr-07 23:11

can you just help me out? Frown | :(

cp987628-Apr-07 0:21

cp9876

28-Apr-07 0:21

google "large integer library c++"

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."