What is Multi-threaded Programming
Multithreading is a fundamental concept in software engineering. In C#, multithreaded programming is essential for software developers working with the .NET Framework. Developers widely use multithreading in C# as it allows them to create complex and responsive applications efficiently.
This blog provides an overview of c# multithreading while, at the same time, also looking at how programmers can create and manage threads easily. It also includes the benefits of using multithreading and the different threading models available in C#.
Benefits and Advantages of Multithreaded Programming
When executed simultaneously, multithreading improves the effectiveness of applications. The most common benefits of the C# thread include the following:
- Enhanced application performance: With the help of multithreading, applications run faster with multiple tasks running in the same space. In its totality, it reduces execution time and gives way to multiple tasks.
- Increased throughput: Multitasking in C# enhances the throughput of applications. When two different threads run concurrently, it can save time and resources.
- Improved responsiveness: With the help of multithreading, a user can access the application’s front end while the program runs in the background.
- Increased resource utilisation: Multithreading allows users to access system resources more efficiently. For instance, threads can share resources like files, memory, and I/O devices, paving the pathway to efficiency.
- More accessible programming: Multithreading allows easier programming as users can write threads independently. It also enables users to debug and test applications in isolation.
- Optimised communication: Thread synchronisation enables better process-to-process communication. It can be used for more accessible communication between threads.
Firstly, it affects single objects which can be synchronised. Secondly, it can be used with the System.Threading and Interlocked class.
Basic Concepts of Multithreading in C#
Multithreading enables users to do multiple tasks simultaneously with the help of multiple processor cores. Here are the basic concepts used in multithreading:
- Threads: Threads are the basic units in multithreading that help execute a process. These are paths of execution within a given program that can run concurrently along with other threads.
In C#, we can find two types of threads, namely foreground and background threads. The average thread class includes a name, priority, isAlive, ThreadState, Start(), Suspend(), Resume(), and Join().
- Thread pool: A thread pool is a thread that helps execute tasks. It allows the operating system to reuse existing threads and minimises the risk of possible overheads.
- Synchronisation: Synchronisation is overlooking access to other threads for multiple operations. It is an essential process to uphold data integrity and prevent overheads.
- Deadlock: A deadlock is an error that occurs when two threads share resources and try to proceed without succeeding. It can cause the system to freeze or even lead to a waiting time.
- Asynchronous programming: Asynchronous programming enables running multiple tasks in the background while allowing the main thread to run without interruption. It paves the way for multiple responsive user interfaces, enhancing application performance.
Creating and Running Threads
Creating and running can be easier with these examples. A C# multithreading example is given below:
using System;
using System.Threading;
class Program {
static void Main() {
int workerIndex = 0;
Thread workerThread = new Thread(new ThreadStart(Worker));
workerThread.Start();
for (int mainIndex = 1; mainIndex <= 10; mainIndex++) {
Console.WriteLine(“Main thread: {0}”, mainIndex);
Thread.Sleep(200);
}
workerThread.Join();
}
static void Worker() {
for (int workerIndex = 1; workerIndex <= 10; workerIndex++) {
Console.WriteLine(“Worker thread: {0}”, workerIndex * 2);
Thread.Sleep(200);
}
}
}
Output:
Main thread: 1
Worker thread: 2
Main thread: 2
Worker thread: 4
Main thread: 3
Worker thread: 6
Main thread: 4
Worker thread: 8
Main thread: 5
Worker thread: 10
Main thread: 6
Worker thread: 12
Main thread: 7
Worker thread: 14
Main thread: 8
Worker thread: 16
Main thread: 9
Worker thread: 18
Main thread: 10
Worker thread: 20
Explanation: In this output, both the threads work concurrently to print numbers 1 to 10 and 2 to 20, the latter doubled from the loop index. In this example, the C# thread sleep (Thread.Sleep) method has been used.
In the same way, we will look at another C# thread example using the foreground thread:
using System;
using System.Threading;
class Program {
static void Main() {
Thread myThread = new Thread(Worker);
myThread.Start();
Console.WriteLine(“Main Thread: Started”);
for (int i = 1; i <= 5; i++) {
Console.WriteLine(“Main Thread: Count {0}”, i);
Thread.Sleep(500);
}
Console.WriteLine(“Main Thread: Ended”);
}
static void Worker() {
for (in j = 1; j <= 5; j++) {
Console.WriteLine(“Worker Thread: Count {0}”, j * 3);
Thread.Sleep(750);
}
Console.WriteLine(“Worker Thread: Ended”);
}
}
Output:
Main Thread: Started
Worker Thread: Count 3
Main Thread: Count 1
Worker Thread: Count 6
Main Thread: Count 2
Worker Thread: Count 9
Main Thread: Count 3
Worker Thread: Count 12
Main Thread: Count 4
Worker Thread: Count 15
Main Thread: Count 5
Worker Thread: Ended
Main Thread: Ended
Explanation: This output shows how the two threads work concurrently. As the main and background threads work in parallel, the main thread prints numbers from 1 to 5. The worker thread prints multiples of 3 to 15.
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Thread Synchronisation
Thread synchronisation involves the collective coordination of multiple threads in a program. It ensures that the program is executed in a specific order giving access to shared resources.
In C#, it is done usig synchronisation primitives like the lock keyword, synchronisation objects, and the Interlocked class.
A C# thread synchronisation example is given below:
Using System;
Using System.Threading;
class TablePrinter
{
public void PrintTable()
{
lock (this)
{
for (int i = 3; i <= 8; i++)
{
Thread.Sleep(200);
Console.WriteLine(i*5);
}
}
}
}
class Program
{
public static void Main(string[] args)
{
TablePrinter tp = new TablePrinter();
Thread t1 = new Thread(new ThreadStart(tp.PrintTable));
Thread t2 = new Thread(new ThreadStart(tp.PrintTable));
t1.Start();
t2.Start();
}
}
Output:
15
20
25
30
35
40
45
50
55
60
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Deadlocks
Deadlocks in multithreading happen when at least two or more two threads depend on a set of resources. When one thread overlaps the route to the help while the other tries to do the same, it becomes a deadlock.
For example, if Thread A has a lock on Resource 1 and is waiting to access Resource 2 while Thread B awaits Resource 1, it can result in a deadlock.
An example is given below:
using System;
using System.Threading;
namespace deadlockincsharp
{
public class Example
{
static readonly object firstLock = new object();
static readonly object secondLock = new object();
static void ThreadJob()
{
Console.WriteLine(“\t\t\t\tLocking firstLock”);
lock (firstLock)
{
Console.WriteLine(“\t\t\t\tLocked firstLock”);
Thread.Sleep(1500);
Console.WriteLine(“\t\t\t\tLocking secondLock”);
lock (secondLock)
{
Console.WriteLine(“\t\t\t\tLocked secondLock”);
}
Console.WriteLine(“\t\t\t\tReleased secondLock”);
}
Console.WriteLine(“\t\t\t\tReleased firstLock”);
}
static void Main()
{
new Thread(new ThreadStart(ThreadJob)).Start();
Thread.Sleep(1000);
Console.WriteLine(“Locking secondLock”);
lock (secondLock)
{
Console.WriteLine(“Locked secondLock”);
Console.WriteLine(“Locking firstLock”);
lock (firstLock)
{
Console.WriteLine(“Locked firstLock”);
}
Console.WriteLine(“Released firstLock”);
}
Console.WriteLine(“Released secondLock”);
Console.Read();
}
}
}
Output:
Locking secondLock
Locked secondLock
Locking firstLock
Locked firstLock
Released firstLock
Released secondLock
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Thread Pools
Thread pools help manage multiple threads of execution in a multithreaded environment in C#. These ensure that all threads have access to controlled resources without giving rise to deadlocks.
A thread pool manager looks after the thread pool, where it is responsible for creating, destroying, and scheduling threads.
Here is an example of a thread pool using TPL (Task Parallel Library):
using System;
using System.Threading.Tasks;
class Program
{
static void Main()
{
Task<string> task = Task.Factory.StartNew<string>
(() => DownloadString(“http://www.example.com/”));
string result = task.Result;
Console.WriteLine(result);
Console.Read();
}
static string DownloadString(string uri)
{
using (var wc = new System.Net.WebClient())
return wc.DownloadString(uri);
}
Output:
The output depends on the contents available on the webpage. This program will ensure downloading contents from the webpage from the specified URL. It will then print them.
Asynchronous Programming with Task Parallel Library (TPL)
The Task Parallel Library (TPL) is a powerful tool for dealing with APIS and public types. It handles System.Threading and System.Threading.Tasks.
The .NET Framework 4 offers language and framework-level APIs for developers aiming to write parallel code. With the help of TPL, asynchronous programming allows programs to run without blocking the main thread.
Here is an example of asynchronous programming with TPL:
Task<string> task = Task.Factory.StartNew<string>(() => {
return “result”;
});
string result = task.Result;
async Task MyMethod() {
string result = await task;
}
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Best Practices for Multithreading in C#
Multithreading can be a time-saver in terms of performance and multitasking. To know more about how multithreading works, you can opt for a Master of Science in Computer Science from LJMU.
Here are a few best practices to help users save time and record the highest efficiency.
- Utilise thread-safe collections: .NET Framework’s concurrent collections provide a thread-safe version of every collection, which makes it easier for multithreading to work efficiently. These collections include lists and queries, and dictionaries.
- Implement thread synchronisation: Users can quickly implement locks, monitors, and semaphores due to the nature of thread tools.
- Use thread-pooling: Multithreading can be easier and more efficient for systems, thanks to the vast majority of thread-pooling done by users. At the same time, users can use it to create threads automatically.
- Use thread-local storage: While practising multithreading, ensure access to a particular resource by optimising thread-local storage and offering access to multiple threads.
- Avoid sharing mutable states: Shared mutable states will only lead to bugs and race conditions, which can be tricky. Ensure to avoid mutable states at any cost.
- Use asynchronous model: Asynchronous methods help you implement multiple tasks in parallel without starting them anew or leaving them in the queue.
- Avoid deadlocks: Deadlocks can be expected when executing programs using multithreading. When writing a program, try running a thread only after another, avoiding deadlocks.
- Use cancellation tokens: Cancellation tokens allow threads to be terminated without issues and avoid deadlocking.
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Conclusion
Multithreading in C# remains an essential concept with its high-efficiency model at work. It provides a flexible way for programmers to divide the workload of a program into multiple tasks running concurrently and independently.
Although multithreading can be highly beneficial, it can lead to potential obstacles if not implemented carefully.
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