IPC (inter-process)
Inter-Process Communication — mechanisms for exchanging data between processes. UNIX mechanisms: pipes, sockets, shared memory, signals, message queues, semaphores. Confusingly similar to IPC (Instructions Per Cycle).
Performance ranking: shared memory (mmap, fastest, needs synchronization yourself), Unix socket (local IPC, ~5µs), pipe (single-stream, ~10µs), TCP loopback (~30µs). Cross-core overhead depends on cache: pipe between processes on same core = L1 hit; between sockets = NUMA roundtrip. Modern alternative: io_uring for async kernel IPC, eBPF maps for low-overhead cross-process state. Classic trap: high-throughput RPC design that ignores IPC overhead → unnecessary serialization between microservices.