Linux internals and network programming: Introduction to IPC

Created by Thomas

IPC (Interprocess Communication)

Communication
- Exchange data between processes
- Can be used between threads of a process, but not necessary because threads can exchange information via shared global variables.

Synchronization:
- Synchronize actions of processes or threads

Types of communications

Types of synchronization

Data transfer:
- Require 2 data transfers between user memory and kernel memory
- For writing, one transfer from user memory to kernel memory
- For reading, another transfer from kernel memory to user memory.

- Byte stream
+ Via pipe, FIFO, datagram socket
+ Read operation: can read arbitrary number of bytes from IPC channel, regardless of size of blocks written by writer.

- Message
+ Via System V message queues, POSIX message queues and datagram socket.
+ Read operation: read a whole message, not possible to read multiple messages on a single read

Below is some examples.

Common illustration of data transfer

Parent-child using two PIPEs

Parent-child using two FIFOs

One server-multiple clients using FIFOs

Client-server using message queue

Shared memory

- Via System V shared memory, POSIX shared memory and memory mapping.
- Allow processes to exchange information by putting it to a region of memory that shared between processes.
- Don't require system calls or data transfer between user and kernel spaces, shared memory can support fast communication.
- However, share memory needs synchronization between processes.

Illustration of shared memory using semaphore.