Use MMAP for inter-process communication in Linux

At the operating system level, the virtual address space seen by each process is independent and there is no intersection between them. Therefore, you need to map different virtual addresses of multiple associated processes to the same physical address space through an intermediate Association. MMAP is such a function. it treats a file (also... information & nbs) as the virtual address space seen by each process is independent at the operating system level and there is no intersection between them. Therefore, you need to map different virtual addresses of multiple associated processes to the same physical address space through an intermediate Association.
 
MMAP is a function that maps a file (that is, the physical address space in the memory) to the address space of different processes.
 
I. write
 
It is worth noting that MMAP requires the physical address space in the memory. Therefore, during the write operation, you need to load the file into the memory for the operation. Therefore, you need to perform the write operation after opening the file, this causes a page missing exception and maps the file to the memory.
 

 
Fd = open (argv [1], O_CREAT | O_RDWR | O_TRUNC, 00777 );
Lseek (fd, 4, SEEK_SET); // here the size is best for the shared struct, and the entire size is loaded into the memory.
Write (fd, "", 1 );
P_mmap = (int *) mmap (NULL, sizeof (int), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 );
Close (fd );
 
* (P_mmap) = 1;
If you do not perform the write null operation, mmap ING will be performed directly, resulting in a segment error because the physical memory corresponding to the actual fd does not exist.
 
 
II. Read
 
The read process must call mmap after the write process. Otherwise, a segment error occurs, which is the same as the previous one.
 
Read Process Flow
 
 
Fd = open (argv [1], O_CREAT | O_RDWR, 0077 );
P_mmap = (int *) mmap (NULL, sizeof (int), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0 );
Printf ("data: % d \ n", (* (p_mmap )));

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