Linux Shared Memory Implementation

The implementation principle of shared memory in Linux is achieved through system calls such as shmget, shmat, and shmdt.

Firstly, you can obtain a shared memory identifier (handle) through the shmget system call, which can be used to create a new shared memory area or to access an existing one.

int shmget(key_t key, size_t size, int shmflg);

In this case, key is a key value used to identify the shared memory area; size is the size of the shared memory area to create or obtain; shmflg is a set of flags used to specify the access rights and creation attributes of the shared memory.

Then, the shared memory is mapped to the address space of the current process through the shmat system call, allowing the process to access the shared memory area. The prototype of the shmat system call is as follows:

void *shmat(int shmid, const void *shmaddr, int shmflg);

“Among them, shmid is the identifier of shared memory; shmaddr is the address for mapping shared memory, and if it is NULL, the system will automatically choose a suitable address; shmflg is some flags used to specify the mapping method of shared memory.”

Finally, the shared memory is detached from the address space of the current process through the shmdt system call, preventing the process from accessing the shared memory area. The prototype of the shmdt system call is as follows:

int shmdt(const void *shmaddr);

“Among them, shmaddr is the mapping address of shared memory.”

Linux manages and accesses shared memory through these system calls, allowing processes to efficiently share data on the same machine.