In today’s fast-paced mobile development world, concurrency isn’t a nice-to-have — it’s foundational. Whether fetching live stock market data or rendering complex UI updates, building responsive and scalable iOS apps requires developers to think in parallel.

At InRhythm, we are deeply committed to promoting best practices in modern software engineering. We champion scalable patterns, clean syntax, and a culture of continuous learning. This article dives into the evolution of concurrency in iOS, offering actionable insights and patterns to modernize your Swift codebase using async/await and TaskGroup.

Why Concurrency Matters

Concurrency is the backbone of responsive apps. It allows tasks — like API calls, data parsing, and UI rendering — to happen simultaneously or asynchronously without blocking the main thread. Whether updating UI elements or aggregating multiple remote data sources, concurrency ensures your app feels fast and fluid.

The Evolution of Concurrency in iOS

1. Dispatch Queues & GCD (Grand Central Dispatch)

The foundation of concurrency in iOS begins with Dispatch Queues, introduced via GCD in Objective-C and later adopted in Swift.

Pros:

• Fine-grained control over thread execution
• Widely supported across iOS versions

Cons:

• Verbose syntax
• Manual thread management
• Nested callbacks leading to unmaintainable asynchronous code

swift
DispatchQueue.global().async {
    // Background work 
   DispatchQueue.main.async { 
        // UI update
   }

}

To simplify GCD, developers began wrapping logic in completion handlers. This enabled asynchronous flows with cleaner APIs and introduced deeply nested code and harder-to-read logic.

swift
fetchData { result in
    parse(result) { parsed in
        updateUI(parsed)
    }
}

3. Combine Framework

Combine is Apple’s declarative framework for managing asynchronous data streams via Publishers and Subscribers.

Pros:

• Declarative and reactive
• Powerful operators for chaining logic

Cons:

• Steeper learning curve
• Verbosity and complexity in larger codebases

4. Async/Await: The Modern Swift Concurrency

Introduced in Swift 5.5 (iOS 15+), async/await revolutionized how iOS developers write concurrent code. It brings simplicity, clarity, and performance, without the downsides of nested callbacks or manual threading.

swift
func fetchData() async throws -> StockSummary {
    let result = try await apiClient.fetchSummary()
    return result
}

Why it shines:

• Clean, readable syntax
• Precise error handling with try/catch
• Fully integrated into the Swift concurrency model

Going Beyond: Task and TaskGroup

As applications grow in complexity, developers need tools that can perform multiple asynchronous tasks in parallel. This is where TaskGroup comes in — a structured concurrency tool that lets you run multiple independent async tasks simultaneously and aggregate their results efficiently.

Use Case: Parallel Network Calls with TaskGroup

Let’s say your app needs to:

• Fetch stock summary from one endpoint
• Retrieve ETF holdings from another

Instead of awaiting each one sequentially, you can execute both in parallel using TaskGroup.

swift
func fetchAllData() async throws {
    try await withTaskGroup(of: Void.self) { group in
        group.addTask {
            try await fetchSummary()
        }
        group.addTask {
            try await fetchTopHoldings()
        }
    }
}

Why This Matters

• True concurrency: Tasks run in parallel, reducing wait time
• Structured cancellation: If one task fails, others are automatically cancelled
• Cleaner code: No more manual thread management or nesting

Best Practices for Swift Concurrency

• Use async/await wherever possible for clarity and simplicity.
• Avoid legacy completion handlers unless needed for backward compatibility.
• Use TaskGroup when making multiple independent API calls.
• Annotate UI-bound functions with @MainActor to ensure thread safety.
• Always handle errors with do-catch to prevent silent failures.

Final Thoughts: Engineering Excellence at InRhythm

At InRhythm, we believe in pushing the boundaries of what’s possible with modern development practices. Our teams do not just build apps — we build scalable, maintainable systems grounded in thoughtful architecture and continuous learning.

By embracing the latest concurrency tools in Swift, like async/await and TaskGroup, our engineers are delivering faster, more responsive, and more resilient applications. We’re passionate about sharing that knowledge to uplift the entire community.

Whether you are just starting with concurrency or refining a production system, these modern Swift techniques will help future-proof your code and level up your development workflow.

Let’s Connect

If you are passionate about building better software and want to work with some of the sharpest minds in the industry, get in touch with us at InRhythm. We are always looking for engineers who care deeply about quality, craftsmanship, and community.

InRhythm, iOS Best Practices, iOS Parallel Programming, iOS TaskGroup, Modern iOS Architecture, Structured Concurrency, Swift 5.5, Swift Concurrency, Swift Performance, Swift UI Threads