ProDeveloperTutorial.com

Tutorials and Programming Solutions
Menu
  • Shell Scripting
  • System Design
  • Linux System Programming
  • 4g LTE
  • Coding questions
  • C
  • C++
  • DSA
  • GIT
  • 450 DSA Cracker
  • 5G NR
  • O-RAN

Linux System Programming: POSIX Shared Memory

prodevelopertutorial May 22, 2020

In this chapter we shall learn about:

1. Introduction

2. API’s used in POSIX Shared Memory

3. Example for POSIX Shared Memory

Introduction:

In the previous chapter we learned about SYS V Shared Memory. In this chapter we shall learn about POSIX Shared Memory.

You need to include below header file for using Shared Memory:

#include <sys/mman.h>

Important functions for using shared memory are:

1. mmap()

void *mmap( void *addr, size_t len, int prot, int flags, int fildes, off_t off );

This function is used to address a memory object.

2. mprotect()

int mprotect( void *addr, size_t len, int prot );

This function is used to change memory protection.

3. munmap()

int munmap( void *addr, size_t len );

This function is used to unmap the memory address that is previously mapped.

4. shm_open()

int shm_open( const char *name, int oflag, mode_t mode );
This function is used to open a shred memory object.

5. shm_unlink()

int shm_unlink( const char *name );

This function is used to remove a shared memory object.

Example for POSIX Shared Memory:

write.c

#include <stdio.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#define FILE_PATH "/my_shm_test"

int main(int argc, char *argv[])
{
	int res;
	int fd;
	int len;
	void *addr;
	char data[256] = "Hello World";


	// get shared memory file descriptor
	fd = shm_open(FILE_PATH, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);

	// increase the size
	res = ftruncate(fd, 256);

	// map shared memory
	addr = mmap(NULL, 256, PROT_WRITE, MAP_SHARED, fd, 0);

	// place data into memory
	len = strlen(data) + 1;
	memcpy(addr, data, len);

	
	sleep(2);

	// mmap cleanup
	res = munmap(addr, 256);

	// shm_open cleanup
	fd = shm_unlink(FILE_PATH);

	return 0;
}

 

read.c

#include <stdio.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define FILE_PATH "/my_shm_test"


int main(int argc, char *argv[])
{
int res;
int fd;
char data[256];
void *addr;

// get shared memory file descriptor
fd = shm_open(FILE_PATH, O_RDONLY, S_IRUSR | S_IWUSR);
if (fd == -1)
{
        perror("open");
        return 10;
}

// map shared memory 
addr = mmap(NULL, 256, PROT_READ, MAP_SHARED, fd, 0);

// place data into memory
memcpy(data, addr, 256);

printf("Read from shared memory: \"%s\"\n", data);

return 0;
}

 

 

List Of Tutorials available in this website:

C Programming 20+ ChaptersC++ Programming 80+ Chapters
100+ Solved Coding QuestionsData Structures and Algorithms 85+ Chapters
System design 20+ ChaptersShell Scripting 12 Chapters
4g LTE 60+ ChaptersMost Frequently asked Coding questions
5G NR 50+ ChaptersLinux System Programming 20+ chapters

 

Share
Email
Tweet
Linkedin
Reddit
Stumble
Pinterest
Prev Article
Next Article

About The Author

prodevelopertutorial

Follow this blog to learn more about C, C++, Linux, Competitive Programming concepts, Data Structures.

Leave a Reply Cancel Reply

You must be logged in to post a comment.

ProDeveloperTutorial.com

Tutorials and Programming Solutions
Copyright © 2023 ProDeveloperTutorial.com
We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. By clicking “Accept”, you consent to the use of ALL the cookies.
Do not sell my personal information.
Cookie SettingsAccept
Manage consent

Privacy Overview

This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary
Always Enabled
Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously.
CookieDurationDescription
cookielawinfo-checkbox-analytics11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checkbox-functional11 monthsThe cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checkbox-necessary11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-others11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-performance11 monthsThis cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy11 monthsThe cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.
Functional
Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance
Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytics
Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement
Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads.
Others
Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
SAVE & ACCEPT