IPC

Inter Process Communication

• https://en.wikipedia.org/wiki/Inter-process_communication#Approaches
• File
• Signals
• Network Sockets
• Unix Domain Sockets
• Anonymous Pipes
• Named Pipes
• Message Queues
• Shared Memory

File

• A record stored on disk which can be accessed by multiple processes

Signals

• See terminal_signals

Network Sockets

• https://en.wikipedia.org/wiki/Network_socket
• used for TCP/IP communication
• The domain passed is AF_INET in socket() method call
• See socket

Unix Domain Sockets

• https://en.wikipedia.org/wiki/Unix_domain_socket
• aka Unix socket or local socket or IPC socket
• The domain passed is AF_UNIX in socket() method call
• Before Windows natively supported Unix domain sockets in late 2017, developers relied on Named Pipes as the primary, high-performance solution for local Inter-Process Communication (IPC)
• Unix socket example: /var/run/docker.sock
  • https://stackoverflow.com/questions/35110146/what-is-the-purpose-of-the-file-docker-sock

Anonymous Pipes

• https://en.wikipedia.org/wiki/Anonymous_pipe
• It is unidirectional data channel using stdin/stdout
• It is FIFO
• Bidirectional communication can be achieved using 2 anonymous pipes
• Examples
  • | in terminal to pass output of one process to another
  • stdio transport in MCP server

Named Pipes

• Instead of using stdin and stdout, special files are created in filesystem
• These special files have no contents on the file system
• They persists unless deleted unlike anonymous pipe which is ephemeral
• It is FIFO

# create a named pipe
mkfifo my_pipe
 
# check file metadata
# prw-r--r--  1 KartikeyKumar  staff  0 28 Jun 17:13 my_pipe
ls -al my_pipe
 
 
# Terminal 1: waits for data
cat my_pipe
 
# Terminal 2: sends data to Terminal 1
echo "Hello from Terminal 2!" > my_pipe
 
# remove the named pipe
rm my_pipe

Message queue

• A data stream similar to a socket, but which usually preserves message boundaries
• Allow multiple processes to read/write to the message queue without being directly connected to each other
• https://man7.org/linux/man-pages/man7/mq_overview.7.html
• https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/mq_send.c;h=b6b70c3ac1f2f3b3fb783abb6566a6cfb538cdc4;hb=HEAD