What is inter-process communication (IPC)?
What is Inter-process communication (IPC)?
Inter-process communication (IPC) provides processes with the capability to communicate with each other. This communication can happen via a variety of ways, using process signals, pipes, message queues, semaphores, and shared memory usage.
Inter-process communication (IPC) provides processes with the capability to communicate with each other. This communication can happen via a variety of ways, using process signals, pipes, message queues, semaphores, and shared memory usage.
Signals
Processes can receive or send a signal to be informed about a specific event or action to take, such as stop running (SIGSTOP, SIGKILL, SIGTERM).
# kill -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
Pipes
Pipes provide the output from one process to another one, typically for further processing.
ps -ef | grep systemd
root 237 1 0 Dec17 ? 00:00:00 /lib/systemd/systemd-journald
root 255 1 0 Dec17 ? 00:00:00 /lib/systemd/systemd-udevd
systemd+ 311 1 0 Dec17 ? 00:00:00 /lib/systemd/systemd-timesyncd
message+ 528 1 0 Dec17 ? 00:00:00 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
root 533 1 0 Dec17 ? 00:00:00 /lib/systemd/systemd-logind
michael 574 1 0 Dec17 ? 00:00:00 /lib/systemd/systemd --user
root 12290 591 0 12:59 pts/0 00:00:00 grep systemd
Semaphores
Semaphores provided a location in memory of which the value can be view and test by multiple processes.
Related syscalls include:
- semctl(2)
- semget(2)
- semop(2)
- semtimedop(2)
Message queues
A message queue provides two or more processes a way to communicate. Each of them opens the message queue using the mq_open(3) function call that includes a name of the queue. Messages then can be shared.
Related syscalls include:
- mq_getsetattr(2)
- mq_notify(2)
- mq_open(2)
- mq_timedreceive(2)
- mq_timedsend(2)
- mq_getsetattr(2)
- mq_timedreceive(2)
- mq_timedsend(2)
- mq_unlink(2)
Shared memory
By using shared memory, processes can communicate via shared virtual address space that is visible to them. Access is controlled via keys and by using some permission checks. When a process is allowed to use the shared memory, it can see those areas.
