/// <summary> /// Uses a lease on a shared resource imposed by the <see cref="ILockManager"/> (i.e an Azure Storage blob or a shared file in a NFS) to provide a mechanism for implementing a shared, distributed mutex. /// </summary> /// <remarks> /// This mutex can be used to elect a leader among a group of role instances in an Azure cloud service or an on-premise infrastructure. /// The first role instance to acquire the lease is elected the leader, and remains the leader until it releases the lease or isn't able to renew the lease. /// </remarks> /// <param name="manager">The instance of <see cref="ILockManager"/>.</param> /// <param name="task">A task that references the code that the role instance should run if it successfully acquires the lease over the blob and is elected the leader.</param> /// <param name="taskName">A name for the task to run.</param> /// <param name="cancellationToken">Propagates notification that operations should be canceled.</param> /// <returns>The task that represents the asynchronous operation result for running the specified delegate.</returns> public static Task ExclusiveRun(this ILockManager manager, string taskName, Func <CancellationToken, Task> task, CancellationToken cancellationToken) => manager.ExclusiveRun(taskName, task, cancellationToken, ExclusiveRunOptions.Default());
/// <summary>
/// Uses a lease on a shared resource imposed by the <see cref="ILockManager"/> (i.e an Azure Storage blob or a shared file in a NFS) to provide a mechanism for implementing a shared, distributed mutex.
/// </summary>
/// <remarks>
/// This mutex can be used to elect a leader among a group of role instances in an Azure cloud service or an on-premise infrastructure.
/// The first role instance to acquire the lease is elected the leader, and remains the leader until it releases the lease or isn't able to renew the lease.
/// </remarks>
/// <param name="manager">The instance of <see cref="ILockManager"/>.</param>
/// <param name="task">A task that references the code that the role instance should run if it successfully acquires the lease over the blob and is elected the leader.</param>
/// <param name="taskName">A name for the task to run.</param>
/// <param name="cancellationToken">Propagates notification that operations should be canceled.</param>
/// <param name="options">Options for configuring the ExclusiveRun method.</param>
/// <returns>The task that represents the asynchronous operation result for running the specified delegate.</returns>
public static async Task ExclusiveRun(this ILockManager manager, string taskName, Func <CancellationToken, Task> task, CancellationToken cancellationToken, ExclusiveRunOptions options)
{
// Run in a while loop as long as cancellation has not been requested for the provided token.
CancellationTokenSource linkedTokenSource = null;
while (!(linkedTokenSource?.IsCancellationRequested ?? false))
{
// Try to acquire the lock.
var lockResult = await manager.TryAcquireLock(taskName, duration : TimeSpan.FromSeconds(options.LockDuration), cancellationToken : cancellationToken);
// If it is not possible to acquire the lock, wait for 30 seconds and try again. Being a leader requires patience and consistency :)
if (!lockResult.Ok)
{
if (options.RetryIntervalInSeconds.HasValue)
{
await Task.Delay(TimeSpan.FromSeconds(options.RetryIntervalInSeconds.Value), cancellationToken);
continue;
}
else
{
break;
}
}
// Create a new linked cancellation token source, so if either the original token is canceled or the lease cannot be renewed, then the leader task can be canceled.
linkedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
// The role instance that is executing the following code is now the leader.
using (lockResult.Lock) {
// The leader task.
var leaderTask = task.Invoke(linkedTokenSource.Token);
// The renew lease task.
var renewLeaseTask = TryRenewUntilCancelled(lockResult.Lock, linkedTokenSource.Token, intervalInSeconds: (int)Math.Round((decimal)options.LockDuration * (2 / 3)));
// Wait for either of the two tasks to complete.
await Task.WhenAny(leaderTask, renewLeaseTask);
}
// Cancel the user's leader task or the renew lease task, as the current role instance is no longer the leader.
linkedTokenSource.Cancel();
}
linkedTokenSource?.Dispose();
}
