what is difference between semaphore and shared memory

Question

What is difference between semaphore and a shared memory ?
can I use semaphores between two different processes or it must be used only in threads of a same process ?

[Semaphore](http://en.wikipedia.org/wiki/Semaphore_(programming)) [Shared Memory](http://en.wikipedia.org/wiki/Shared_memory) — Arnab Nandy, Nov 16 '14 at 17:06

score 3 · Answer 1 · edited May 23 '17 at 10:28

3

Yes, you can use semaphore between two different processes

Choose a name for your semaphore

#define SNAME "/mysem"

Use sem_open with O_CREAT in the process that creates them

sem_t *sem = sem_open(SNAME, O_CREAT, 0644, 3); /* Initial value is 3. */

Open semaphores in the other processes

sem_t *sem = sem_open(SEM_NAME, 0); /* Open a preexisting semaphore. */

Reference

edited May 23 '17 at 10:28

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answered Nov 16 '14 at 17:11

Arnab Nandy

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this is answer of part 2 only the part one given in your comment check it – Arnab Nandy Nov 16 '14 at 17:29

score 3 · Answer 2 · answered Nov 16 '14 at 17:50

The semaphore is a system for synchronization 2 or plus process to access a shared resource.

The shared memory is a system for sharing a piece of memory between 2 o plus process, on the shared memory is possible write or read data to and from a process.

For example with a semaphore is possible to manage the access to shared memory for avoid the read o write non synchronized from 2 process.

Bye

what is difference between semaphore and shared memory

2 Answers2