Thread, Process, Goroutines: Definitions, How They Work, Differences, and Utility
1. Process
Definition:
A process is an independent program in execution, with its own memory space, code, data, and system resources.
How it works:
- The operating system (OS) creates a process when you run a program.
- Each process is isolated from others; it cannot directly access another process's memory.
- Communication between processes (Inter-Process Communication, IPC) is possible but more complex (e.g., pipes, sockets).
Utility:
- Used for running separate applications or services.
- Good for isolation and security (a crash in one process doesn't affect others).
2. Thread
Definition:
A thread is the smallest unit of execution within a process. Multiple threads can exist within the same process, sharing the same memory and resources.
How it works:
- Threads within the same process share code, data, and resources, but each has its own execution stack and program counter.
- Threads are lighter than processes and can communicate more easily (since they share memory).
- The OS schedules threads for execution, often on different CPU cores.
Utility:
- Used for parallelism within a single application (e.g., handling multiple user requests, background tasks).
- More efficient than processes for tasks that need to share data.
3. Goroutine
Definition:
A goroutine is a lightweight thread managed by the Go runtime (not the OS), used in the Go programming language.
How it works:
- Goroutines are multiplexed onto a smaller number of OS threads by the Go runtime scheduler.
- They are extremely lightweight (a few KB of stack space) and can be created in large numbers.
- Communication and synchronization between goroutines are typically done using channels.
Utility:
- Ideal for concurrent programming in Go (e.g., web servers, parallel computations).
- Makes it easy to write scalable, concurrent code without worrying about OS thread management.
Key Differences
| Aspect | Process | Thread | Goroutine |
|---|---|---|---|
| Memory | Separate per process | Shared within process | Shared within process |
| Creation Cost | High | Medium | Very Low |
| Scheduling | By OS | By OS | By Go runtime |
| Communication | IPC (complex) | Shared memory (easy) | Channels (easy, safe) |
| Crash Impact | Isolated | Can affect process | Can affect process |
| Language | Any | Any | Go only |
Summary of Utility
- Processes: Use for strong isolation, running separate programs/services.
- Threads: Use for parallelism within a program, sharing data easily.
- Goroutines: Use in Go for massive concurrency with minimal overhead.
Deep Dive: Threads and Processes
Is a Process Always Made Up of Threads?
Short Answer:
Yes, in modern operating systems, every process has at least one thread.
Explanation
-
Single-threaded Process:
- When a process is created, it starts with a single thread, often called the "main thread."
- This thread executes the program's code.
- If the program never creates additional threads, it remains a single-threaded process.
-
Multi-threaded Process:
- A process can create additional threads to perform tasks concurrently.
- All threads within a process share the same memory and resources.
-
Thread as the Execution Unit:
- In modern OSes, a thread is the actual unit of execution.
- Even if you don't explicitly create threads, the OS creates at least one thread for your process to run.
Historical Context
- Older Systems:
- In very old or simple operating systems, the concept of threads didn't exist. The process itself was the unit of execution.
- Modern systems (Windows, Linux, macOS, etc.) always use threads, even if you don't see them directly.
Summary Table
| Scenario | Threads Present? | Notes |
|---|---|---|
| Modern OS, any process | Yes (at least 1) | Main thread always exists |
| Multi-threaded program | Yes (many) | Threads created for concurrency |
| Old/simple OS | No (historically) | Process = execution unit, no thread concept |
Key Point:
Every process in a modern OS has at least one thread (the main thread). Multi-threaded processes have more.
Deep Dive: Routines (Goroutines, Coroutines, Threads) and Core Utilization
What is a Routine?
- "Routine" is a general term for a function or procedure. In concurrency, it often refers to goroutines (Go), coroutines (Python, Lua, Kotlin), or threads.
How Do Routines Work Behind the Scenes?
1. Goroutines (Go)
- Managed by the Go runtime, not the OS.
- When you start a goroutine, it's scheduled by the Go scheduler, which multiplexes many goroutines onto a smaller number of OS threads.
- The Go runtime automatically manages the mapping of goroutines to OS threads and can move goroutines between threads as needed.
- By default, Go will use as many OS threads as there are CPU cores (configurable with
GOMAXPROCS). - The Go scheduler tries to keep all CPU cores busy by distributing goroutines across available threads/cores.
- If you have many goroutines and multiple CPU cores, Go can run them in parallel, maximizing CPU utilization.
2. Coroutines (General, e.g., Python asyncio)
- Coroutines are functions that can pause and resume their execution (using
await,yield, etc.). - They are scheduled cooperatively, meaning they yield control back to the event loop, which then runs the next coroutine.
- Coroutines are not OS threads; they run in a single thread unless you explicitly use threads or processes.
- By default, coroutines run on a single OS thread and thus on a single CPU core.
- To utilize multiple cores, you need to combine coroutines with multiprocessing or threading.
3. Threads (General)
- Threads are managed by the OS.
- Each thread can be scheduled on any available CPU core by the OS scheduler.
- Multiple threads can run in parallel on multiple cores.
- If you create multiple threads, the OS can run them on different CPU cores, allowing true parallelism (especially for CPU-bound tasks).
Summary Table
| Type | Managed By | Parallelism | Core Utilization | Notes |
|---|---|---|---|---|
| Goroutine | Go runtime | Yes | Across multiple cores | Efficient, lightweight, Go-specific |
| Coroutine | Language/runtime | No (by default) | Single core (unless combined with threads/processes) | Cooperative multitasking, not true parallelism |
| Thread | OS | Yes | Across multiple cores | True parallelism, heavier than goroutines/coroutines |
How the Process Works Behind the Scenes
- You start a routine (goroutine/coroutine/thread).
- Scheduler (OS or language runtime) decides when and where to run it.
- If multiple CPU cores are available:
- Threads and goroutines can be run in parallel on different cores.
- Coroutines (by default) run on one core unless you use multiple processes/threads.
- The scheduler balances the workload to maximize CPU utilization.
In summary:
- Goroutines and threads can utilize multiple CPU cores for parallel execution.
- Coroutines, by default, do not utilize multiple cores unless combined with other concurrency mechanisms.
- The underlying scheduler (OS or language runtime) is responsible for distributing work across available cores.