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DistributedLock.Azure.md

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DistributedLock.Azure

Download the NuGet package NuGet Status

The DistributedLock.Azure package offers distributed locks based on Azure blob leases. For example:

var container = new BlobContainerClient(myAzureConnectionString, "my-locking-container-name");
var @lock = new AzureBlobLeaseDistributedLock(container, "MyLockName");
await using (var handle = await @lock.TryAcquireAsync())
{
  if (handle != null) { /* I have the lock */ }
}

APIs

  • The AzureBlobLeaseDistributedLock class implements the IDistributedLock interface.
  • The AzureBlobLeaseDistributedSynchronizationProvider class implements the IDistributedLockProvider interface.

Implementation notes

AzureBlobLeaseDistributedLocks can be constructed either from a BlobContainerClient and a name, which will cause it to lease a blob in the provided container with a name based on the provided name. If you know exactly which blob you'd like to lease, another constructor lets you pass a BlobBaseClient instead.

Because of how Azure leases work, the acquire operation cannot truly block. If waiting to acquire a lock that is not available, the implementation will periodically sleep and retry until the lease can be taken or the acquire timeout elapses. Because of this, these locks are maximally efficient when using TryAcquire semantics with a timeout of zero.

Blob leases in Azure have built-in expirations. However while an AzureBlobLeaseDistributedLock is held it will periodically renew the lease in the background. Therefore, it is generally safe to ignore the problem of lease duration.

Options

In addition to specifying the blob to be leased, several tuning options are provided. You should not need to change these options most of the time.

  • Duration changes the blob lease duration requested under the hood
  • RenewalCadence changes how frequently auto-renewal re-ups the lease duration while holding the lock
  • BusyWaitSleepTime specifies a range of times that the implementation will sleep between attempts to acquire a lease that is currently held by someone else. A random number in the range will be chosen for each sleep. If you expect contention, lowering these values may increase the responsiveness (how quickly a lock detects that it can now take the lease) but will increase the number of API calls made to Azure. Raising the values will have the reverse effects.