concurrency-limiter

About

concurrency-limiter allows you to limit the number of goroutines accessing a resource with support for timeouts , dynamic priority of goroutines and context cancellation of goroutines.

The library now supports two admission modes:

• strict admission via Wait / Run
• soft admission via WaitOrBypass / RunOrBypass

Installation

To install concurrency-limiter:

go get github.com/vivek-ng/concurrency-limiter

Then import concurrency-limiter to use it

    import(
        "time"
        github.com/vivek-ng/concurrency-limiter/limiter
    )

    nl := limiter.New(3)
    ctx := context.Background()
    if err := nl.Wait(ctx); err != nil {
        return
    }
    // Perform actions .........
    nl.Finish()

Usage

Below are some examples of using this library. To run real examples , please check the examples folder.

Limiter

    import(
        "time"
        github.com/vivek-ng/concurrency-limiter/limiter
    )

    func main() {
        nl := limiter.New(3)

        var wg sync.WaitGroup
        wg.Add(15)

        for i := 0; i < 15; i++ {
            go func(index int) {
                defer wg.Done()
                ctx := context.Background()
                if err := nl.Wait(ctx); err != nil {
                    return
                }
                // in real life , this can be DB operations , message publish to queue ........
                fmt.Println("executing action...: ", "index: ", index, "current number of goroutines: ", nl.Count())
                nl.Finish()
            }(i)
        }
        wg.Wait()
    }

Priority Limiter

    import(
        "time"
        github.com/vivek-ng/concurrency-limiter/priority
    )
    
    func main() {
        pr := priority.NewLimiter(1)
        var wg sync.WaitGroup
        wg.Add(15)
        for i := 0; i < 15; i++ {
            go func(index int) {
                defer wg.Done()
                ctx := context.Background()
                if index%2 == 1 {
                    if err := pr.Wait(ctx, priority.High); err != nil {
                        return
                    }
                } else {
                    if err := pr.Wait(ctx, priority.Low); err != nil {
                        return
                    }
                }
                // in real life , this can be DB operations , message publish to queue ........
                fmt.Println("executing action...: ", "index: ", index, "current number of goroutines: ", pr.Count())
                pr.Finish()
            }(i)
        }
        wg.Wait()
    }

Examples

Limiter

    nl := limiter.New(3)
    ctx := context.Background()
    if err := nl.Wait(ctx); err != nil {
        return
    }
    // Perform actions .........
    nl.Finish()

In the above example , there can be a maximum of 3 goroutines accessing a resource concurrently. The other goroutines are added to the waiting list and are removed and given a chance to access the resource in the FIFO order. If the context is cancelled , the goroutine is removed from the waitlist and Wait returns the context error.

Limiter with Timeout

    nl := limiter.New(3,
    WithTimeoutDuration(10 * time.Millisecond),
    )
    ctx := context.Background()
    if err := nl.Wait(ctx); err != nil {
        return
    }
    // Perform actions .........
    nl.Finish()

In the above example , the goroutines will wait for a maximum of 10 milliseconds. Goroutines will be removed from the waitlist after 10 ms and Wait will return limiter.ErrTimeout.

Limiter with Soft Timeout

    nl := limiter.New(3,
    WithTimeoutDuration(10 * time.Millisecond),
    )
    ctx := context.Background()
    result, err := nl.WaitOrBypass(ctx)
    if err != nil {
        return
    }
    if result == limiter.AdmissionAcquired {
        defer nl.Finish()
    }
    // Perform actions .........

In the above example , the goroutine waits for up to 10 milliseconds to acquire real capacity. If capacity is still unavailable after the timeout, WaitOrBypass returns limiter.AdmissionBypassed and the caller can still proceed without consuming limiter capacity.

Priority Limiter

    nl := priority.NewLimiter(3)
    ctx := context.Background()
    if err := nl.Wait(ctx , priority.High); err != nil {
        return
    }
    // Perform actions .........
    nl.Finish()

In Priority Limiter , goroutines with higher priority will be given preference to be removed from the waitlist. For instance in the above example , the goroutine will be given the maximum preference because it is of high priority. In the case of tie between the priorities , the goroutines will be removed from the waitlist in the FIFO order.

Priority Limiter with Dynamic priority

    nl := priority.NewLimiter(3,
    WithDynamicPriorityDuration(5 * time.Millisecond),
    )
    ctx := context.Background()
    if err := nl.Wait(ctx , priority.Low); err != nil {
        return
    }
    // Perform actions .........
    nl.Finish()

In Dynamic Priority Limiter , the goroutines with lower priority will get their priority increased periodically by the time period specified. For instance in the above example , the goroutine will get it's priority increased every 5 ms. This will ensure that goroutines with lower priority do not suffer from starvation. It's highly recommended to use Dynamic Priority Limiter to avoid starving low priority goroutines.

Priority Limiter with Timeout

    nl := priority.NewLimiter(3,
    WithTimeoutDuration(30 * time.Millisecond),
    WithDynamicPriorityDuration(5 * time.Millisecond),
    )
    ctx := context.Background()
    if err := nl.Wait(ctx , priority.Low); err != nil {
        return
    }
    // Perform actions .........
    nl.Finish()

This is similar to the timeouts in the normal limiter. In the above example , goroutines will wait a maximum of 30 milliseconds and Wait will return limiter.ErrTimeout if capacity is not acquired in time. The low priority goroutines will get their priority increased every 5 ms.

Priority Limiter with Soft Timeout

    nl := priority.NewLimiter(3,
    WithTimeoutDuration(30 * time.Millisecond),
    WithDynamicPriorityDuration(5 * time.Millisecond),
    )
    ctx := context.Background()
    result, err := nl.WaitOrBypass(ctx , priority.Low)
    if err != nil {
        return
    }
    if result == limiter.AdmissionAcquired {
        defer nl.Finish()
    }
    // Perform actions .........

This uses the same soft-admission model for the priority limiter. The goroutine waits up to the configured timeout while still participating in the priority queue. If capacity is not acquired in time, the call returns limiter.AdmissionBypassed and the caller may continue outside the limiter.

Runnable Function

    nl := priority.NewLimiter(3)
    ctx := context.Background()
    nl.Run(ctx , priority.Low , func()error {
        return sendMetrics()
    })

Runnable function will allow you to wrap your function and execute them with concurrency limit. This function is a wrapper on top of the Wait() and Finish() functions. If Wait fails because the context is cancelled or the timeout expires, Run returns that error and does not execute the callback.

Runnable Function with Soft Timeout

    nl := priority.NewLimiter(3,
    WithTimeoutDuration(30 * time.Millisecond),
    )
    ctx := context.Background()
    result, err := nl.RunOrBypass(ctx , priority.Low , func()error {
        return sendMetrics()
    })
    if err != nil {
        return
    }
    _ = result

RunOrBypass executes the callback after either real admission or timeout bypass. It returns limiter.AdmissionAcquired when the limiter granted capacity and limiter.AdmissionBypassed when the callback ran outside the limiter after the timeout.

The older WithTimeout(int) and WithDynamicPriority(int) helpers are still supported for compatibility and continue to interpret their arguments as milliseconds.

Contribution

Please feel free to open up issues , create PRs for bugs/features. All contributions are welcome :)