Interprocess Communication (IPC)

Official Definition: Interprocess communication (IPC) is used for programs to communicate data to each other and to synchronize their activities. Semaphores, shared memory, and internal message queues are common methods of interprocess communication.

What it means:
IPC is a method for two or more separate programs or processes to communicate with each other. This avoids using real disk-based files and the associated I/O overhead to pass information. Like a file, you must first create or open the resource, use it and close it. Like real files, the resources have an owner, a group, and permissions. Until you remove the resource it continues to exist. Unlike real disk-based files, semaphores, message queues and shared memory do not persist across reboots.

Approaches to Interprocess Communication
The different approaches to implement interprocess communication are given as follows − Pipes: Pipe is widely used for communication between two related processes. This is a half-duplex method, so the first process communicates with the second process. However, in order to achieve a full-duplex, another pipe is needed.

• Message Passing: It is a mechanism for a process to communicate and synchronize. Using message passing, the process communicates with each other without resorting to shared variables. IPC mechanism provides two operations:
  • Send (message)- message size fixed or variable
  • Received (message)
• Message Queues: A message queue is a linked list of messages stored within the kernel. It is identified by a message queue identifier. This method offers communication between single or multiple processes with full-duplex capacity.
• Direct Communication: In this type of inter-process communication process, should name each other explicitly. In this method, a link is established between one pair of communicating processes, and between each pair, only one link exists.
• Indirect Communication: Indirect communication establishes like only when processes share a common mailbox each pair of processes sharing several communication links. A link can communicate with many processes. The link may be bi-directional or unidirectional.
• Shared Memory: Shared memory is a memory shared between two or more processes that are established using shared memory between all the processes. This type of memory requires to protected from each other by synchronizing access across all the processes.
• FIFO: Communication between two unrelated processes. It is a full-duplex method, which means that the first process can communicate with the second process, and the opposite can also happen.