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DistributedCacheLocker.cs

using Microsoft.Extensions.Caching.Distributed;
using Newtonsoft.Json;

namespace Nop.Core.Caching;

public partial class DistributedCacheLocker : ILocker
{
    #region Fields

    protected static readonly string _running = JsonConvert.SerializeObject(TaskStatus.Running);
    protected readonly IDistributedCache _distributedCache;

    #endregion

    #region Ctor

    public DistributedCacheLocker(IDistributedCache distributedCache)
    {
        _distributedCache = distributedCache;
    }

    #endregion

    #region Methods

    /// 
    /// Performs some asynchronous task with exclusive lock
    /// 
    /// The key we are locking on
    /// The time after which the lock will automatically be expired
    /// Asynchronous task to be performed with locking
    /// A task that resolves true if lock was acquired and action was performed; otherwise false
    public async Task PerformActionWithLockAsync(string resource, TimeSpan expirationTime, Func action)
    {
        //ensure that lock is acquired
        if (!string.IsNullOrEmpty(await _distributedCache.GetStringAsync(resource)))
            return false;

        try
        {
            await _distributedCache.SetStringAsync(resource, resource, new DistributedCacheEntryOptions
            {
                AbsoluteExpirationRelativeToNow = expirationTime
            });

            await action();

            return true;
        }
        finally
        {
            //release lock even if action fails
            await _distributedCache.RemoveAsync(resource);
        }
    }

    /// 
    /// Starts a background task with "heartbeat": a status flag that will be periodically updated to signal to
    /// others that the task is running and stop them from starting the same task.
    /// 
    /// The key of the background task
    /// The time after which the heartbeat key will automatically be expired. Should be longer than 
    /// The interval at which to update the heartbeat, if required by the implementation
    /// Asynchronous background task to be performed
    /// A CancellationTokenSource for manually canceling the task
    /// A task that resolves true if lock was acquired and action was performed; otherwise false
    public async Task RunWithHeartbeatAsync(string key, TimeSpan expirationTime, TimeSpan heartbeatInterval, Func action, CancellationTokenSource cancellationTokenSource = default)
    {
        if (!string.IsNullOrEmpty(await _distributedCache.GetStringAsync(key)))
            return;

        var tokenSource = cancellationTokenSource ?? new CancellationTokenSource();

        try
        {
            // run heartbeat early to minimize risk of multiple execution
            await _distributedCache.SetStringAsync(
                key,
                _running,
                new DistributedCacheEntryOptions { AbsoluteExpirationRelativeToNow = expirationTime },
                token: tokenSource.Token);

            await using var timer = new Timer(
                callback: _ =>
                {
                    try
                    {
                        tokenSource.Token.ThrowIfCancellationRequested();
                        var status = _distributedCache.GetString(key);
                        if (!string.IsNullOrEmpty(status) && JsonConvert.DeserializeObject(status) ==
                            TaskStatus.Canceled)
                        {
                            tokenSource.Cancel();
                            return;
                        }

                        _distributedCache.SetString(
                            key,
                            _running,
                            new DistributedCacheEntryOptions { AbsoluteExpirationRelativeToNow = expirationTime });
                    }
                    catch (OperationCanceledException) { }
                },
                state: null,
                dueTime: 0,
                period: (int)heartbeatInterval.TotalMilliseconds);

            await action(tokenSource.Token);
        }
        catch (OperationCanceledException) { }
        finally
        {
            await _distributedCache.RemoveAsync(key);
        }
    }

    /// 
    /// Tries to cancel a background task by flagging it for cancellation on the next heartbeat.
    /// 
    /// The task's key
    /// The time after which the task will be considered stopped due to system shutdown or other causes,
    /// even if not explicitly canceled.
    /// A task that represents requesting cancellation of the task. Note that the completion of this task does not
    /// necessarily imply that the task has been canceled, only that cancellation has been requested.
    public async Task CancelTaskAsync(string key, TimeSpan expirationTime)
    {
        var status = await _distributedCache.GetStringAsync(key);
        if (!string.IsNullOrEmpty(status) &&
            JsonConvert.DeserializeObject(status) != TaskStatus.Canceled)
            await _distributedCache.SetStringAsync(
                key,
                JsonConvert.SerializeObject(TaskStatus.Canceled),
                new DistributedCacheEntryOptions { AbsoluteExpirationRelativeToNow = expirationTime });
    }

    /// 
    /// Check if a background task is running.
    /// 
    /// The task's key
    /// A task that resolves to true if the background task is running; otherwise false
    public async Task IsTaskRunningAsync(string key)
    {
        return !string.IsNullOrEmpty(await _distributedCache.GetStringAsync(key));
    }

    #endregion
}