Shared Memory in Operating Systems is an Inter-Process Communication (IPC) method that allows processes to exchange data using a common memory space. Since each process normally has its own address space, they cannot directly access each other’s data. To share information, a portion of memory is marked as shared, which can then be accessed by multiple processes for reading and writing. This makes data sharing fast and efficient.
Working of Shared Memory
Let us consider two processes P1 and P2 that want to perform Inter-process communication using a shared memory.
P1 has an address space, let us say A1 and P2 has an address space, let us say A2. Now, P1 takes up some of the available address space as a shared memory space, let us say S1. Since P1 has taken up this space, it can decide which other processes can read and write data from the shared memory space.
For now, we will assume that P1 has given only reading rights to other processes with respect to the shared memory. So, the flow of Inter-process communication will be as follows:
- Process P1 takes up some of the available space as shared memory S1
- Process P1 writes the data to be shared in S1
- Process P2 reads the shared data from S1
Now, let us assume that P1 has given write rights to P2 as well. So the communication will shown in the below diagram:
Since P1 took up the space for shared memory i.e. since process P1 is the creator process, only it has the right to destroy the shared memory as well.
Use Cases of Shared Memory
- Inter-Process Communication: Shared memory is primarily used in IPC where two processes need a shared address space in order to exchange data.
- Parallel Processing: Multiple processes can share and modify data in the shared address space, thereby speeding up computations.
- Databases: Shared memory is used in databases, in the form of cache, so that reading and writing of data can be much faster
- Graphics and Multimedia Applications: CPU and GPU can access data concurrently which is helpful in tasks such as video manipulation and processing.
- Distributed Systems: Two different machines can access data from a shared space and work as a single system.
Advantages
- Shared memory is one of the fastest means of IPC since it avoids overheads.
- Easy access to data once set up.
- It is memory efficient as processes do not need to separately store shared data.
Disadvantages
- Since it is operating system specific, it is difficult to implement common synchronization and authorization techniques.
- Memory leaks can take place.
- If the processes wait indefinitely for each other in order to release the shared memory space, a deadlock can occur.