Asynchronous task is a non-blocking task. Main thread goes back to the thread pool (and free to do other tasks) when it reaches to await – and new thread is assigned when wait is complete.
It is different from the multi-threading. In multi-threding, task is divided between multiple threads. Cores of your CPU are utilized.
Analogy
Let’s say you have some chores like:
- Boiling eggs 🫕 (or sweet potatoes🍠🍠 if you dont eat eggs 🥚🥚)
- Clean 🧹🪣 the house
There are multiple ways to achieve this:
- Boil the eggs 🥚 and wait until it finishes, then clean 🧹🪣 the house. It is called
synchronous task. - You put eggs 🥚 in boiling water and set the timer ⏰. Meanwhile you finishes other works like clean a house🧹🪣. When timer ⏰ indicates, you close the lit of boiling pan 🫕. Then again you finishes the remaining task. It is called
asynchronous task. You are not bound to wait for the task to finish. - You has asked someone to boil the eggs🫕 and you are taking care of cleaning 🧹🪣 the house. You are two people 👥 now. It is called
multi-threading, you have more workers to finish the task.
Synchronous task
namespace ConsoleApp;
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine($"Main thread : {Thread.CurrentThread.ManagedThreadId}");
BoilEggs();
CleanHouse();
Console.WriteLine($"All task completed by ThreadId: {Thread.CurrentThread.ManagedThreadId}");
}
public static void BoilEggs()
{
Console.WriteLine("Eggs are boiling...");
Thread.Sleep(2000);
Console.WriteLine($"Egg boiled by thread : {Thread.CurrentThread.ManagedThreadId}");
}
public static void CleanHouse()
{
Console.WriteLine("Cleaning in process..");
Thread.Sleep(1500);
Console.WriteLine($"House cleaned by thread : {Thread.CurrentThread.ManagedThreadId}");
}
}
Output:
Main thread : 1
Eggs are boiling...
# wait for 2 sec
Egg boiled by thread : 1
Cleaning in process..
# wait for 1.5 sec
House cleaned by thread : 1
All task complete by ThreadId: 1
As you have noticed, all the task are finished by a single thread.
Asynchronous Task
namespace ConsoleApp;
public class Program
{
public static async Task Main(string[] args)
{
Console.WriteLine($"Main thread : {Thread.CurrentThread.ManagedThreadId}");
await BoilEggs();
await CleanHouse();
await SomeOtherChore();
Console.WriteLine($"All task completed by ThreadId: {Thread.CurrentThread.ManagedThreadId}");
}
public static async Task BoilEggs()
{
Console.WriteLine("Eggs are boiling...");
await Task.Delay(2000);
Console.WriteLine($"Egg boiled by thread : {Thread.CurrentThread.ManagedThreadId}");
}
public static async Task CleanHouse()
{
Console.WriteLine("Cleaning in process..");
await Task.Delay(1500);
Console.WriteLine($"House cleaned by thread : {Thread.CurrentThread.ManagedThreadId}");
}
public static async Task SomeOtherChore()
{
Console.WriteLine("SomeOther chore in process..");
await Task.Delay(500);
Console.WriteLine($"SomeOther chore is completed by thread : {Thread.CurrentThread.ManagedThreadId}");
}
}
Output:
Main thread : 1
Eggs are boiling...
# main thread is released
# waiting for 2 sec
# Thread by id 5 has joined in
Egg boiled by thread : 5
Cleaning in process..
# Thread 5 is released
# wait for 1.5 sec
# Thread 5 has joined back
House cleaned by thread : 5
SomeOther chore in process..
# thread 5 is released
# waiting for 500 ms
# thread 5 has joined back
SomeOther chore is completed by thread : 5
All task completed by ThreadId: 5
You can also wait all task at once.
Console.WriteLine($"Main thread : {Thread.CurrentThread.ManagedThreadId}");
Task boilEggTask = BoilEggs();
Task cleanHouseTask = CleanHouse();
Task otherChoreTask = SomeOtherChore();
await Task.WhenAll(boilEggTask, cleanHouseTask, otherChoreTask);
Console.WriteLine($"All task completed by ThreadId: {Thread.CurrentThread.ManagedThreadId}");
output:
Main thread : 1
# threa 1 is released
# waiting for all the task to finished
Eggs are boiling...
Cleaning in process..
SomeOther chore in process..
# thread 5 has joined in
# all tasks are completed at once in the background
SomeOther chore is completed by thread : 5
House cleaned by thread : 5
Egg boiled by thread : 5
All task completed by ThreadId: 5
Multi-threading
using System.Diagnostics.CodeAnalysis;
namespace ConsoleApp;
public class Program
{
public static void Main(string[] args)
{
Console.WriteLine($"Main thread : {Thread.CurrentThread.ManagedThreadId}");
Thread t1 = new Thread(BoilEggs);
Thread t2 = new Thread(CleanHouse);
Thread t3 = new Thread(SomeOtherChore);
t1.Start();
t2.Start();
t3.Start();
t1.Join();
t2.Join();
t3.Join();
}
public static void BoilEggs()
{
Console.WriteLine("Eggs are boiling...");
Thread.Sleep(2000);
Console.WriteLine($"Egg boiled by thread : {Thread.CurrentThread.ManagedThreadId}");
}
public static void CleanHouse()
{
Console.WriteLine("Cleaning in process..");
Thread.Sleep(1500);
Console.WriteLine($"House cleaned by thread : {Thread.CurrentThread.ManagedThreadId}");
}
public static void SomeOtherChore()
{
Console.WriteLine("SomeOther chore in process..");
Thread.Sleep(500);
Console.WriteLine($"SomeOther chore is completed by thread : {Thread.CurrentThread.ManagedThreadId}");
}
}
output:
Main thread : 1
# All task are running simultaniously by different thread
# Tasks will finish in the order of shortest execution task
Eggs are boiling...
Cleaning in process..
SomeOther chore in process..
SomeOther chore is completed by thread : 6 # It has the shortest time
House cleaned by thread : 5 # it is second shortest
Egg boiled by thread : 4 # it has longest time
Real life use case of async
string url = "https://jsonplaceholder.typicode.com/users";
HttpClient client = new();
var data = await client.GetStringAsync(url);
Console.WriteLine(data);
When to choose each?
Async is useful in IO bound tasks like network calls, database calls or manipulating files.
multi-threading is useful in CPU bound tasks like image/video processing, encryption/hashing or processing the large data.