共享内存----实现进程间通信

C++使用共享内存实现进程间通信

　　文件映射是一种实现进程间单向或双向通信的机制。它允许两个或多个本地进程间相互通信。为了共享文件或内存，所有的进程必须使用相同的文件映射的名字或是句柄。

　　为了实现共享文件，第一个进程先调用CreateFile方法。接下来调用CreateFileMapping方法来创建一个文件映射对象。并为文件映射指明一个句柄和名称。由于事件，信号，互斥对象和文件映射等这些内核对象都共享同一个名字空间，所以如果这个名字和其他一个对象的名称重名的话那么将创建失败。

　　为了实现共享内存，进程应首先调用CreateFileMapping函数然后在hFile参数中传入INVALID_HANDLE_VALUE宏来替代句柄。相应的文件映射对象会从系统的分页文件中获得一段内存。如果hFile参数的值是INVALID_HANDLE_VALUE，那么你在调用CreateFileMapping时必须给共享内存指定一个大小值。

　　使用共享内存或文件的进程必须使用MapViewOfFile函数或MapViewOfFileEx函数来创建一个文件视图。

　　下面我们创建一个名称为"Local\SampleMap"的文件映射对象，并将一个字符串写入到文件映射中。

　　我们将创建两个程序，一个是服务程序，一个是客户程序。服务程序负责创建文件映射。

　　服务程序命名为CppFileMappingServer，它的执行过程是

　　1、创建一个特定大小的文件映射对象，名称为“Local\SampleMap”

　　2、将这个对象的文件视图映射到进程的地址空间，然后向视图中写入字符串。

　　接下来执行客户程序CppFileMappingClient，它首先打开这个名称为“Local\SampleMap”的文件映射对象。然后把相同的文件映射视图映射到自己的地址空间中。然后从视图中读取服务进程所写入的数据。

　　Server完整源码：

#pragma region Includes
#include <stdio.h>
#include <windows.h>
#pragma endregion
#define MAP_PREFIX          L"Local\\"
#define MAP_NAME            L"SampleMap"
#define FULL_MAP_NAME       MAP_PREFIX MAP_NAME

// Max size of the file mapping object.
#define MAP_SIZE            65536

// File offset where the view is to begin.
#define VIEW_OFFSET         0

// The number of bytes of a file mapping to map to the view. All bytes of the
// view must be within the maximum size of the file mapping object (MAP_SIZE).
// If VIEW_SIZE is 0, the mapping extends from the offset (VIEW_OFFSET) to
// the end of the file mapping.
#define VIEW_SIZE           1024

// Unicode string message to be written to the mapped view. Its size in byte
// must be less than the view size (VIEW_SIZE).
#define MESSAGE             L"Message from the first process."

int wmain(int argc, wchar_t* argv[])
{
HANDLE hMapFile = NULL;
PVOID pView = NULL;

// Create the file mapping object.
hMapFile = CreateFileMapping(
INVALID_HANDLE_VALUE,   // Use paging file - shared memory
NULL,                   // Default security attributes
PAGE_READWRITE,         // Allow read and write access
0,                      // High-order DWORD of file mapping max size
MAP_SIZE,               // Low-order DWORD of file mapping max size
FULL_MAP_NAME           // Name of the file mapping object
);
if (hMapFile == NULL)
{
wprintf(L"CreateFileMapping failed w/err 0x%08lx\n", GetLastError());
goto Cleanup;
}
wprintf(L"The file mapping (%s) is created\n", FULL_MAP_NAME);

// Map a view of the file mapping into the address space of the current
// process.
pView = MapViewOfFile(
hMapFile,               // Handle of the map object
FILE_MAP_ALL_ACCESS,    // Read and write access
0,                      // High-order DWORD of the file offset
VIEW_OFFSET,            // Low-order DWORD of the file offset
VIEW_SIZE               // The number of bytes to map to view
);
if (pView == NULL)
{
wprintf(L"MapViewOfFile failed w/err 0x%08lx\n", GetLastError());
goto Cleanup;
}
wprintf(L"The file view is mapped\n");

// Prepare a message to be written to the view.
PWSTR pszMessage = MESSAGE;
DWORD cbMessage = (wcslen(pszMessage) + 1) * sizeof(*pszMessage);

// Write the message to the view.
memcpy_s(pView, VIEW_SIZE, pszMessage, cbMessage);

wprintf(L"This message is written to the view:\n\"%s\"\n",
pszMessage);

// Wait to clean up resources and stop the process.
wprintf(L"Press ENTER to clean up resources and quit");
getchar();

Cleanup:

if (hMapFile)
{
if (pView)
{
// Unmap the file view.
UnmapViewOfFile(pView);
pView = NULL;
}
// Close the file mapping object.
CloseHandle(hMapFile);
hMapFile = NULL;
}

return 0;
}

Client完整源码：

#pragma region Includes
#include <stdio.h>
#include <windows.h>
#pragma endregion
#define MAP_PREFIX          L"Local\\"
#define MAP_NAME            L"SampleMap"
#define FULL_MAP_NAME       MAP_PREFIX MAP_NAME

// File offset where the view is to begin.
#define VIEW_OFFSET         0

// The number of bytes of a file mapping to map to the view. All bytes of the
// view must be within the maximum size of the file mapping object. If
// VIEW_SIZE is 0, the mapping extends from the offset (VIEW_OFFSET) to the
// end of the file mapping.
#define VIEW_SIZE           1024

int wmain(int argc, wchar_t* argv[])
{
HANDLE hMapFile = NULL;
PVOID pView = NULL;

// Try to open the named file mapping identified by the map name.
hMapFile = OpenFileMapping(
FILE_MAP_READ,          // Read access
FALSE,                  // Do not inherit the name
FULL_MAP_NAME           // File mapping name
);
if (hMapFile == NULL)
{
wprintf(L"OpenFileMapping failed w/err 0x%08lx\n", GetLastError());
goto Cleanup;
}
wprintf(L"The file mapping (%s) is opened\n", FULL_MAP_NAME);

// Map a view of the file mapping into the address space of the current
// process.
pView = MapViewOfFile(
hMapFile,               // Handle of the map object
FILE_MAP_READ,          // Read access
0,                      // High-order DWORD of the file offset
VIEW_OFFSET,            // Low-order DWORD of the file offset
VIEW_SIZE               // The number of bytes to map to view
);
if (pView == NULL)
{
wprintf(L"MapViewOfFile failed w/err 0x%08lx\n", GetLastError());
goto Cleanup;
}
wprintf(L"The file view is mapped\n");

// Read and display the content in view.
wprintf(L"Read from the file mapping:\n\"%s\"\n", (PWSTR)pView);

// Wait to clean up resources and stop the process.
wprintf(L"Press ENTER to clean up resources and quit");
getchar();

Cleanup:

if (hMapFile)
{
if (pView)
{
// Unmap the file view.
UnmapViewOfFile(pView);
pView = NULL;
}
// Close the file mapping object.
CloseHandle(hMapFile);
hMapFile = NULL;
}

return 0;
}

运行效果：

　　Server




　　Client