Understanding Processes vs. Threads: Definitions, Differences, and Trade‑offs

1. Definition

A process is an independent execution activity of a program on a data set, serving as the unit of resource allocation and scheduling in the system.

A thread is an entity of a process and the basic unit of CPU scheduling; it is a smaller, independently runnable unit. Threads do not own system resources except essential ones such as a program counter, a set of registers, and a stack, but they share all resources of their parent process.

2. Relationship

A thread can create and terminate another thread; multiple threads within the same process can execute concurrently.

Compared with a process, a thread is closer to the execution entity: it can share data with other threads in the same process while having its own stack space and independent execution sequence.

3. Differences

The main distinction lies in resource management. A process has an independent address space; if a process crashes, it does not affect others. A thread is merely a different execution path within a process, sharing the same address space. If a thread dies, the whole process terminates, making multi‑process programs more robust, though process switching consumes more resources and is less efficient.

However, for tasks that require simultaneous execution and shared variables, threads are necessary, whereas processes are not suitable.

In short:

Every program has at least one process, and each process has at least one thread.

Threads have a finer granularity than processes, giving higher concurrency.

Processes have separate memory spaces, while multiple threads share memory, greatly improving execution efficiency.

Threads cannot run independently; they depend on the application to create and control them.

From a logical perspective, threads allow multiple execution parts within one application, but the operating system schedules and manages resources at the process level.

4. Advantages and Disadvantages

Threads have low execution overhead but are harder to manage and protect resources; processes have higher overhead but provide better isolation and can migrate across machines.

Via: http://blogread.cn/it/article/7445