public async Task <bool> TryLock()
{
try
{
_lease = _blobLeaseFactory.CreateLease(_blob);
_leaseId = await _lease.TryAcquireLease();
if (_leaseId == null)
{
DisposeLease();
return(false);
}
await _blob.FetchAttributesAsync();
if (_blob.Metadata.ContainsKey(UpdateDomainInstancesKey))
{
string[] instanceIds = _blob.Metadata[UpdateDomainInstancesKey].Split(',');
_instanceIds = new HashSet <string>(instanceIds);
}
_updateDomain = _blob.Metadata.ContainsKey(UpdateDomainKey) ? _blob.Metadata[UpdateDomainKey] : string.Empty;
return(true);
}
catch (StorageException e)
{
DisposeLease();
Trace.TraceInformation($"Failed to acquire the lease on blob {_blob.Name}", e);
return(false);
}
}
public async Task <bool> TryStartUpdateSession(string applicationId)
{
string updateBlobName = GetUpdateBlobName(applicationId);
bool started = false;
try
{
ICloudBlob updateBlob = GetBlob(updateBlobName);
await CreateBlobIfNoneExists(updateBlob);
IBlobLease blobLease = _blobLeaseFactory.CreateLease(updateBlob);
ExceptionDispatchInfo capturedException = null;
string leaseId = await blobLease.TryAcquireLease();
// allow this instance to update only if it can acquire a lease on the blob.
if (leaseId == null)
{
Trace.TraceInformation("Cannot start update session because unable to acquire the lease on the blob");
return(false);
}
try
{
var updateBlobWrapper = await UpdateBlobWrapper.Create(updateBlob);
var updateDomain = updateBlobWrapper.GetUpdateDomain();
HashSet <string> updateDomainInstancesHashset = updateBlobWrapper.GetInstanceIds();
// allow this instance to try updating only if either one of the following conditions are true:
// 1. no update domain is set,
// 2. the current instance is in the same update domain
// 3. no instances are set for the current update domain
if (string.IsNullOrEmpty(updateDomain) ||
_config.InstanceUpdateDomain == updateDomain ||
updateDomainInstancesHashset.Count == 0)
{
Trace.TraceInformation(
"Instance {0} acquired a lock on update blob {1} and will attempt to enlist itself",
_config.InstanceId, updateBlobName);
updateDomainInstancesHashset.Add(_config.InstanceId);
await
updateBlobWrapper.SetData(leaseId, _config.InstanceUpdateDomain,
updateDomainInstancesHashset);
Trace.TraceInformation("Instance {0} enlisted itself in the update blob", _config.InstanceId);
started = true;
}
}
catch (Exception e)
{
capturedException = ExceptionDispatchInfo.Capture(e);
}
await blobLease.ReleaseLease();
Trace.TraceInformation("Instance {0} released the lock on update blob {1}", _config.InstanceId, updateBlobName);
if (capturedException != null)
{
capturedException.Throw();
}
return(started);
}
catch (Exception ex)
{
throw new Exception("Failed to start update session ", ex);
}
}