private bool AcquireLeaseIfBlobExists(TimeSpan leaseDuration)
{
bool exists = true;
StorageOperation.Try(
() => { AcquireLeaseForExistingBlob(leaseDuration); },
catchHttp404: e => { exists = false; }
);
return(exists);
}
private void AcquireLeaseForExistingBlob(TimeSpan leaseDuration)
{
StorageOperation.Try(
() =>
{
lock (this.writeAccessCondition)
{
this.writeAccessCondition.LeaseId = this.backingBlob.AcquireLease(leaseDuration, proposedLeaseId: null);
}
},
catchHttp409: e =>
{
throw new InvalidOperationException("The lease for this blob has been taken by another client", e);
});
}
private void WriteLocalDataToCloudIfNeeded()
{
lock (this.syncRoot)
{
byte[] localContentHash;
if (!Serialization.ModifiedSince(
this.localObject,
this.lastKnownBlobContentsHash,
out localContentHash))
{
return;
}
AccessCondition writeAccessConditionAtStartOfUpload = new AccessCondition();
lock (this.writeAccessCondition)
{
writeAccessConditionAtStartOfUpload.LeaseId = this.writeAccessCondition.LeaseId;
}
StorageOperation.Try(
() =>
{
OperationContext context = new OperationContext();
CloudBlobStream uploadStream = this.backingBlob.OpenWrite(
accessCondition: writeAccessConditionAtStartOfUpload,
operationContext: context);
Serialization.SerializeIntoStream(this.localObject, uploadStream);
uploadStream.Close();
this.readAccessCondition.IfNoneMatchETag = context.LastResult.Etag;
this.lastKnownBlobContentsHash = localContentHash;
},
catchHttp400: e =>
{
// Can happen when two clients race to perform an upload to the same blob; one
// client will get a HTTP 400 when committing their list of uploaded blocks.
OnWriteToCloudFailure(e, writeAccessConditionAtStartOfUpload);
},
catchHttp412: e =>
{
// There is a lease in place that prevents this write.
OnWriteToCloudFailure(e, writeAccessConditionAtStartOfUpload);
});
}
}
private bool TryRefreshDataFromCloudBlob()
{
bool exists = true;
StorageOperation.Try(
() =>
{
T temp = default(T);
OperationContext context = new OperationContext();
lock (this.syncRoot)
{
StorageOperation.Try(
() =>
{
Stream blobContentsStream = this.backingBlob.OpenRead(
accessCondition: this.readAccessCondition,
operationContext: context);
exists = Serialization.DeserializeInto <T>(
ref temp,
blobContentsStream,
out this.lastKnownBlobContentsHash);
this.readAccessCondition.IfNoneMatchETag = context.LastResult.Etag;
},
catchHttp404: e =>
{
exists = false;
});
this.localObject = temp;
if (exists)
{
if (this.OnUpdate != null)
{
this.OnUpdate(this, EventArgs.Empty);
}
}
}
},
catchHttp304: e => { }, // TODO: Perf improvement; prevent throwing of exceptions in expected-case paths?
catchHttp412: e => { });
return(exists);
}
/// <summary>
/// Starts a task that triggers a request to renew the lease on the backing blob MinimumLeaseInSeconds
/// before it expires, and releases the lease when the task is aborted.
/// </summary>
private Task StartLeaseRenewer(TimeSpan leaseDuration)
{
return(Task.Run(
() =>
{
Stopwatch timer = Stopwatch.StartNew();
bool stop = false;
while (!stop)
{
stop = stopLeaseRenewer.Wait(TimeSpan.FromTicks(timer.ElapsedTicks % (leaseDuration.Ticks / 2)));
if (!stop)
{
StorageOperation.Try(
() =>
{
lock (this.writeAccessCondition)
{
this.backingBlob.RenewLease(this.writeAccessCondition);
}
},
catchHttp409: e =>
{
// Lost our original lease (maybe due to this task sleeping for an extremely long time)
AcquireLeaseForExistingBlob(leaseDuration);
});
}
}
StorageOperation.Try(
() =>
{
lock (this.writeAccessCondition)
{
this.backingBlob.ReleaseLease(this.writeAccessCondition);
}
},
catchHttp409: e =>
{
// Maybe we didn't have the lease anyway? Ooh well, we're shutting down anyway (absorb this error)
});
}));
}
