Concurrency and Parallelism -

Concurrency

The composition of independently executing tasks.
Applied when dealing with handling lots of things at once.
The focus is on how to structure a solution to solve a problem which may or may not be solved in a parallel manner.
Concurrency is a way to structure a program by breaking it into pieces that can be executed independently.
Communication is the means to coordinate the independent executions.
Go supports concurrency. Go provides:
- concurrent execution (goroutines).
- synchronization and messaging (channels).
- multi-way concurrent control (select).
IMPORTANT POINTS:
- Concurrency is powerful.
- Concurrency is not parallelism.
- Concurrency enables parallelism.
- Concurrency makes parallelism (and scaling and everything else) easy.

“Concurrency is about dealing with lots of things at once. Parallelism is about doing lots of things at once.” — Rob Pike
- Concurrency is a property of a program where two or more tasks can be in progress simultaneously. Parallelism is a run-time property where two or more tasks are being executed simultaneously. Through concurrency you want to define a proper structure to your program. Concurrency can use parallelism for getting its job done but remember parallelism is not the ultimate goal of concurrency.
Concurrency is about dealing with lots of things at once.
Parallelism is about doing lots of things at once.
Not the same, but related.
Concurrency is about structure, parallelism is about execution.
Concurrency provides a way to structure a solution to solve a problem that may (but not necessarily) be parallelizable.
An analogy
- Concurrent: Mouse, keyboard, display, and disk drivers.
- Parallel: Vector dot product.