Parallel Execution and Asynchronous Programming in C++

Parallel execution and asynchronous programming are both techniques used to improve the efficiency and performance of C++ programs, but they serve different purposes and interact in interesting ways.

Parallel Execution:

• Focuses on dividing a task into smaller sub-tasks that can be executed simultaneously.
• Typically uses multiple threads to perform tasks concurrently.
• Commonly achieved using execution policies like std::execution::par and thread management libraries.

Asynchronous Programming:

• Focuses on non-blocking operations, allowing tasks to start, pause, and resume without waiting for each other.
• Uses constructs like std::async, std::future, and std::promise to manage asynchronous tasks.
• Often employed to handle I/O-bound operations, improving responsiveness without necessarily using multiple threads.

Interaction Between Parallel and Asynchronous Programming: Combining these techniques can lead to powerful and responsive applications. For instance, you can execute multiple asynchronous tasks in parallel, improving both computation and responsiveness.

Here's an example that demonstrates the interaction:

1#include <execution>
2#include <future>
3#include <iostream>
4#include <thread>
5#include <vector>
6
7void Log(int number) {
8  std::this_thread::sleep_for(
9    std::chrono::seconds(1));
10  std::cout << "Number: " << number << '\n';
11}
12
13int main() {
14  std::vector<int> numbers{1, 2, 3, 4, 5};
15
16  // Asynchronous tasks executed in parallel
17  std::vector<std::future<void>> futures;
18  for (int number : numbers) {
19    futures.push_back(std::async(
20      std::launch::async, Log, number));
21  }
22
23  // Wait for all tasks to complete
24  for (auto& future : futures) {
25    future.get();
26  }
27}

1Number: 4
2Number: 3
3Number: 2
4Number: 1
5Number: 5

In this example:

• std::async is used to launch asynchronous tasks.
• Each task runs the Log() function in parallel, thanks to std::launch::async.
• The main thread waits for all tasks to complete using future.get().

Key Points:

• Parallel Execution uses multiple threads for simultaneous task execution.
• Asynchronous Programming allows tasks to run without blocking the main thread.
• Combining both techniques can enhance performance and responsiveness.
• Use std::async with std::launch::async to execute tasks asynchronously in parallel.

By understanding how these techniques interact, you can write more efficient and responsive C++ programs, leveraging the best of both worlds.