What is DispatchGroup and when should we use it?

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DispatchGroup allows developers to manage groups of tasks that run concurrently. It helps to synchronize multiple asynchronous tasks and wait for all of them to complete before moving on to the next task.

The DispatchGroup class provides enter() & leave() methods, to manage tasks that are executed asynchronously. When a task is started, you call the enter() method, and when the task is finished, you call the leave() method. The DispatchGroup class keeps track of the number of uncompleted tasks in the group, and when the count reaches zero, the notify() method is called, indicating that all tasks in the group have completed.

Suppose you will display average weather for several cities, by fetching weather data asynchronously…

let group = DispatchGroup()
let cities = ["New York", "London", "Tokyo"]
var weatherData = [String: Weather]()
for city in cities {
    fetchWeather(for: city) { result in
        weatherData[city] = result
group.notify(queue: .main) {
    // All data has been fetched
    updateUI(with: weatherData)

DispatchGroup is useful in situations where you have multiple asynchronous tasks that need to be synchronized before proceeding to the next task. It simplifies the code by providing a structured way to manage tasks that are executed concurrently, and ensures that all tasks have completed before continuing with the next step.

✍️ Written by Ishtiak Ahmed

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