Oleh sebab setiap process mempunyai ruang alamat terasing, mereka tidak boleh sekadar berkongsi pembolehubah — mereka memerlukan komunikasi antara process (inter-process communication, IPC). OS menawarkan beberapa mekanisme, berbeza dari segi kelajuan, arah, dan sama ada ia berfungsi merentas mesin.
Mekanisme utama
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Pipe / FIFO → byte stream, one direction; anonymous pipe = parent↔child, named FIFO = any procs
e.g. ls | grep foo (the shell wires stdout→stdin via a pipe)
Shared memory → both map the SAME physical pages → FASTEST (no copy), but you must
synchronize access yourself (semaphore/mutex)
Message queue → kernel-managed queue of discrete messages; decoupled, preserves boundaries
Socket → bidirectional stream/datagram; UNIX-domain (same host) or TCP/UDP (across network)
Signal → tiny async notification (a number), e.g. SIGINT, SIGTERM — control, not data transfer