Mapping a File for Shared Memory

Mapping a File for Shared Memory

You can use mmap() simply to create a segment of memory that can be shared among unrelated processes:

In one process, create a file to represent the segment.
Typically the file is located in /var/tmp, but it can be anywhere. The file permissions determine the access permitted to other processes.
In another process, get a file descriptor using open() or the POSIX function shm_open(), specifying the file path.
In that other process, use mmap() specifying the file descriptor of the file.

Tip: The usinit() function is a more convenient and general way of creating a shared arena. It is based on mmap() but adds other services--see "Allocating in a Shared Arena". You can also create a shared segment of memory using SVR4-compatible shared memory functions; see "System V Shared Memory".