How much faster will work be with coroutines compared to executing a calculation function without coroutines and threads?

Executing work with coroutines by itself does not make it "faster" compared to synchronous execution on a single thread. Coroutines allow efficient management of asynchronous operations, avoiding thread blocking and context switching, which leads to:

1. Improved UI responsiveness: The main thread is not blocked, which is important for user interface.
2. Efficient resource utilization: Less overhead compared to creating and managing multiple traditional threads.
3. Simplification of asynchronous code: Sequential style of writing asynchronous operations.

If the calculation function is purely computational and does not include blocking operations (e.g., input-output, network requests), then executing this function:

• Without coroutines and threads (synchronously on the main thread): Blocks the thread, UI hangs during calculation.
• With coroutines: The task runs in a thread pool (e.g., Dispatchers.Default for CPU-intensive tasks). It does not block the main thread, but the total execution time may be similar or even slightly longer due to coroutine scheduling overhead.
• With a separate traditional thread: The task runs in a separate thread, not blocking the main thread. The overhead of creating and managing the thread may be higher than with coroutines.

Thus, for purely CPU-intensive calculations without blocking operations, using coroutines or a separate thread will not make the computational work itself faster. The benefit of coroutines (or threads) in this scenario is in not blocking the main thread, which is critically important for maintaining a smooth and responsive user interface.

In fact, during pure CPU-intensive calculations:

// Synchronously on the current thread (may block)
fun calculateSync() {
    // Long calculation
}

// With coroutines (in Dispatchers.Default)
suspend fun calculateWithCoroutines() = withContext(Dispatchers.Default) {
    // Long calculation
}

// With a traditional thread
fun calculateWithThread() {
    Thread {
        // Long calculation
    }.start()
}

The "Long calculation" itself will take approximately the same time in any of these cases, assuming they run on CPU cores. The perception of work by the user and the application's ability to perform other tasks simultaneously will be faster.

For tasks involving blocking operations (e.g., file reading), coroutines using appropriate dispatchers (e.g., Dispatchers.IO) allow to "free" the thread on which they were launched to execute other coroutines, instead of blocking it as a traditional thread waiting for the operation to complete. In this scenario, coroutines can lead to significantly improved resource utilization and system throughput compared to using a large number of traditional threads for blocking tasks.