Process vs Thread: Isolation vs Shared Execution
Overview A process is an independently executing program instance with its own private address space, while a thread is a lightweight unit of execution that runs inside a process and shares that process’s memory with its sibling threads. The distinction matters because it determines how much isolation, communication overhead, and crash-safety you get versus how cheap context switching and data sharing are. Comparison Diagram Process Thread Process A Code Data Heap Stack Process B Code Data Heap Stack no shared memory (IPC only) single process address space Shared Code / Data / Heap Thread 1 Stack Registers Thread 2 Stack Registers Thread 3 Stack Registers shared heap/code, private stack per thread Comparison Table Aspect Process Thread Memory space Own isolated virtual address space Shares address space with sibling threads in the same process Creation cost Expensive (fork/CreateProcess, new page tables) Cheap (allocate stack + TCB, reuse existing address space) Context switch cost Higher (flush TLB, swap page tables) Lower (same address space, just swap registers/stack pointer) Communication Requires IPC: pipes, sockets, shared memory, message queues Direct via shared variables/heap; needs locks/mutexes for safety Fault isolation A crash typically stays contained to that process A crash (e.g. bad pointer, unhandled exception) can take down the whole process Scheduling unit OS schedules processes (which contain ≥ 1 thread) OS (or runtime) schedules threads independently within a process Concurrency primitives needed Rarely needed within a single process Mutexes, semaphores, atomics to guard shared state Typical use case Running separate, independently-failing programs (browser tabs as processes, microservices) Parallelizing work within one program (web server handling many requests, UI thread + workers) Key Differences A thread lives inside a process and shares its code, heap, and open file handles; a process owns its own private address space. Threads communicate by directly reading/writing shared memory (needing synchronization); processes must use explicit IPC mechanisms. Creating and context-switching a thread is much cheaper than doing the same for a process, since no new address space or page table is involved. A crashing thread can corrupt or kill its entire parent process; a crashing process is generally isolated from other processes by the OS. Multiple threads share one process’s resource limits (file descriptors, memory quota); each process gets its own. When to Use Each Process ...