Shared Memory: Another problem

This is a one C# application.

The first section of the code is just a decleration to import window API from Kernel32.dll. This is just so I can get access to the memory. This is the code that I've received from my first post: http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=469838&SiteID=1

The second section is the main part of the code that use the imported API to create a named shared memory called "TestSharedMemory". It should be receiving information from the shared segment of the memory.

When I run the C# code alone, it was able to access the part of the memory. I have done couple of stepping through and it looks like it actually points to a memory location and would read data from it (but the data would be "null" because there is on other application writing data to it). However, if the I run the same C# application while the C application is running, the C# pointer would points to null instead of a memory location.

It seems like the C# and C application are pointing to the same memory location, but if they're running at the same time the C application would locks the C# one out.

Here is the C code (Notice that it is very similar to the main function in C#):

#include <stdio.h>
#include <windows.h>

void main(int argc, char* argv[])
{
HANDLE mappedFile = 0;
int oneSecond = 1000;
char* shared = NULL;
HANDLE eventHnd;

eventHnd = CreateEvent(NULL, FALSE, FALSE, "TestSharedEvent");

mappedFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL,
PAGE_READWRITE, 0, 4096, "TestSharedMemory");
printf("CreateFileMapping returned %d\n", mappedFile);
fflush(NULL);

shared = (char*)MapViewOfFile(mappedFile, FILE_MAP_WRITE, 0, 0, 0);
printf("MapViewOfFile returned %p\n", shared);
fflush(NULL);

memset(shared, 0, 4096);
printf("memset worked\n");
fflush(NULL);

int counter = 0;
while (1)
{
sprintf(shared, "value %d", counter++);
printf("Sending new string: %s\n", shared);
SetEvent(eventHnd);
// STEP 5
Sleep(1000);
}

UnmapViewOfFile(shared);
}

I also tried running two C application at the same time (one sending and the other receiving the memory) , and it works just fine.

adroit2 at 2007-9-10 >

There's two application in total, one C# and one C. I thought you were asking if the code in my original post was two seperate application, that code is for one application.

Give me another try. Here is the working prototype code that I've got. If you run the master code, it will start sending information to the memory. If you, then, start up the slave code, it will starts receiving the information from the memory.

I just want to convert the slave code to C#.

EXE file #1: Mater C code sending information:

#include <stdio.h>
#include <windows.h>

void main(int argc, char* argv[])
{
HANDLE mappedFile = 0;
int oneSecond = 1000;
char* shared = NULL;
HANDLE eventHnd;

eventHnd = CreateEvent(NULL, FALSE, FALSE, "TestSharedEvent");

// STEP 1
mappedFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL,
PAGE_READWRITE, 0, 4096, "TestSharedMemory");
printf("CreateFileMapping returned %d\n", mappedFile);
fflush(NULL);

// STEP 2
shared = (char*)MapViewOfFile(mappedFile, FILE_MAP_WRITE, 0, 0, 0);
printf("MapViewOfFile returned %p\n", shared);
fflush(NULL);

memset(shared, 0, 4096);
printf("memset worked\n");
fflush(NULL);

int counter = 0;
while (1)
{
sprintf(shared, "value %d", counter++);
printf("Sending new string: %s\n", shared);
SetEvent(eventHnd);
// STEP 5
Sleep(1000);
}

UnmapViewOfFile(shared);
}

EXE File #2 Slave C code receiving information:

#include <stdio.h>
#include <windows.h>

#define SCREEN_SIZE (320*240/8)

void main(int argc, char* argv[])
{
HANDLE mappedFile = 0;
int oneSecond = 1000;
char* shared = NULL;
HANDLE eventHnd;

eventHnd = CreateEvent(NULL, FALSE, FALSE, "TestSharedEvent");

// STEP 1
mappedFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL,
PAGE_READWRITE, 0, SCREEN_SIZE, "TestSharedMemory");
printf("CreateFileMapping returned %d\n", mappedFile);
fflush(NULL);

// STEP 2
shared = (char*)MapViewOfFile(mappedFile, FILE_MAP_WRITE, 0, 0, 0);
printf("MapViewOfFile returned %p\n", shared);
fflush(NULL);

memset(shared, 0, 4096);
int value = 0;

printf("memset worked\n");
fflush(NULL);

while (1)
{
WaitForSingleObject(eventHnd, INFINITE);
// STEP 5
printf("New value %s\n", shared);
Sleep(oneSecond);
}

UnmapViewOfFile(shared);
}

Make File:

CPPFILES1 = master.cpp
CPPFILES2 = slave.cpp

OBJS1 = $(CPPFILES1:s;.cpp;$O;)
OBJS2 = $(CPPFILES2:s;.cpp;$O;)

EXETARGET1 = master$E
EXETARGET2 = slave$E

link: deps $(EXETARGET1) $(EXETARGET2)

$(EXETARGET1): $(OBJS1)

$(EXETARGET2): $(OBJS2)

deps:: includes$(DEP)
includes$(DEP): $(CPPFILES1) $(CPPFILES2)
.INCLUDE .IGNORE : includes$(DEP)

I know that I am terrible at explaining things, sorry about that. I am trying though. Is that a little more clear? Or do you need more info? I'm not sure what other information you need to make this more clear.

Thank you, for trying to help. I truly appreciate it.

adroit2 at 2007-9-10 >