DZone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
Refcards Trend Reports
Events Video Library
Refcards
Trend Reports

Events

View Events Video Library

Zones

Culture and Methodologies Agile Career Development Methodologies Team Management
Data Engineering AI/ML Big Data Data Databases IoT
Software Design and Architecture Cloud Architecture Containers Integration Microservices Performance Security
Coding Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks
Culture and Methodologies
Agile Career Development Methodologies Team Management
Data Engineering
AI/ML Big Data Data Databases IoT
Software Design and Architecture
Cloud Architecture Containers Integration Microservices Performance Security
Coding
Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance
Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks

Last call! Secure your stack and shape the future! Help dev teams across the globe navigate their software supply chain security challenges.

Modernize your data layer. Learn how to design cloud-native database architectures to meet the evolving demands of AI and GenAI workloads.

Releasing software shouldn't be stressful or risky. Learn how to leverage progressive delivery techniques to ensure safer deployments.

Avoid machine learning mistakes and boost model performance! Discover key ML patterns, anti-patterns, data strategies, and more.

Related

  • Low-Level Optimizations in ClickHouse: Utilizing Branch Prediction and SIMD To Speed Up Query Execution
  • Testing the Untestable and Other Anti-Patterns
  • Coordinating Threads Using CountDownLatch
  • Enterprise Architecture Governance: A Holistic View

Trending

  • Mastering Advanced Aggregations in Spark SQL
  • The Cypress Edge: Next-Level Testing Strategies for React Developers
  • Comprehensive Guide to Property-Based Testing in Go: Principles and Implementation
  • Concourse CI/CD Pipeline: Webhook Triggers
  1. DZone
  2. Software Design and Architecture
  3. Integration
  4. call_once for C#

call_once for C#

By 
Dror Helper user avatar
Dror Helper
·
Mar. 06, 14 · Interview
Likes (0)
Comment
Save
Tweet
Share
6.7K Views

Join the DZone community and get the full member experience.

Join For Free

One of the useful gems that made it into C++11 Standard Template Libraries (STD) is call_once, this nifty little method makes sure that specific code is called only once (duh) and it follows these 3 rules:

  • Exactly one execution of exactly one of the functions (passed as f to the invocations in the group) is performed. It is undefined which function will be selected for execution. The selected function runs in the same thread as

    thecall_once invocation it was passed to.

  • No invocation in the group returns before the abovementioned execution of the selected function is completed successfully, that is, doesn't exit via an exception.
  • If the selected function exits via exception, it is propagated to the caller. Another function is then selected and executed.

I needed something similar – I had a method that should only be called once (initialize) and I wanted to implement something similar to the call_once I’ve been using for my C++ development.

My first object was to try and make it as preferment as possible and so I’ve looked for a solution that does not involve locks:

public static class Call
{
    public static void Once(OnceFlag flag,  Action action)
    {
        if (flag.CheckIfNotCalledAndSet)
        {
            action.Invoke();            
        }
    }
}

since I was  trying to mimic the C++ code I wrote two objects Call (above) and OnceFlag which has all of the magic inside using Interlocked:

public class OnceFlag
{
    private const int NotCalled = 0;
    private const int Called = 1;
    private int _state = NotCalled;
    internal bool CheckIfCalledAndSet
    {
        get
        {
            var prev = Interlocked.Exchange(ref _state, Called);
            
            return prev == NotCalled;
        }
    }

    internal void Reset()
    {
        Interlocked.Exchange(ref _state, NotCalled);
    }
}

I’m using Interlocked as a thread-safe way to check & set the value making sure that only once it would return true – try it:

class Program
{
    static OnceFlag _flag = new OnceFlag();
    static void Main(string[] args)
    {
        var t1 = new Thread(() => DoOnce(1));
        var t2 = new Thread(() => DoOnce(2));
        var t3 = new Thread(() => DoOnce(3));
        var t4 = new Thread(() => DoOnce(4));

        t1.Start();
        t2.Start();
        t3.Start();
        t4.Start();

        t1.Join();
        t2.Join();
        t3.Join();
        t4.Join();
    }

    private static void DoOnce(int index)
    {
        Call.Once(_flag, () => Console.WriteLine("Callled (" + index + ")"));
    }
}

It’s very simple solution unfortunately not entirely correct –  the method used will only be called once, but requirements 2 & 3 were not implemented. Luckily for me I didn’t need to make sure that exception enable another call to pass through nor did I need to block other calls until the first call finishes.

But I wanted to try and write a proper implementation, unfortunately not as preferment due to the use of locks:

public static void Once(OnceFlagSimple flag, Action action)
{
    lock (flag)
    {        
        if (flag.CheckIfNotCalled)
        {
            action.Invoke();
    
            flag.Set();            
        }
    }
}

But it works, and since I’m already using lock I can split the check and Set methods and use a bool value inside the flag instead of Interlocked.

  • All other threads are blocked due to lock until first finish running – check!
  • In case of exception other method can execute the once block – check!
  • If exited properly the block would only execute once – check!

But not very good performance due to locking even after the first time run.

I’m still looking for a better way to implement call_once – it’s a good exercise in threading and I might find a cool new ways to use the classes under Threading or Task namespaces.

please let me know if you have a better implementation – that’s what the comments are for…

Threading code style Execution (computing) Blocks IT Implementation Template c++ Pass (software)

Published at DZone with permission of Dror Helper, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

Related

  • Low-Level Optimizations in ClickHouse: Utilizing Branch Prediction and SIMD To Speed Up Query Execution
  • Testing the Untestable and Other Anti-Patterns
  • Coordinating Threads Using CountDownLatch
  • Enterprise Architecture Governance: A Holistic View

Partner Resources

×

Comments

The likes didn't load as expected. Please refresh the page and try again.

ABOUT US

  • About DZone
  • Support and feedback
  • Community research
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • Become a Contributor
  • Core Program
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 3343 Perimeter Hill Drive
  • Suite 100
  • Nashville, TN 37211
  • support@dzone.com

Let's be friends: