public async Task Add(CachedEvent e)
{
if (null == e)
throw new KeenException("Cached events may not be null");
var keenFolder = await getKeenFolder()
.ConfigureAwait(continueOnCapturedContext: false);
IFile file;
var attempts = 0;
var done = false;
string name = null;
do
{
attempts++;
// Avoid race conditions in parallel environment by locking on the events queue
// and generating and inserting a unique name within the lock. CreateFileAsync has
// a CreateCollisionOption.GenerateUniqueName, but it will return the same name
// multiple times when called from parallel tasks.
// If creating and writing the file fails, loop around and
if (string.IsNullOrEmpty(name))
lock (events)
{
var i = 0;
while (events.Contains(name = e.Collection + i++))
;
events.Enqueue(name);
}
Exception lastErr = null;
try
{
file = await keenFolder.CreateFileAsync(name, CreationCollisionOption.FailIfExists)
.ConfigureAwait(continueOnCapturedContext: false);
var content = JObject.FromObject(e).ToString();
await file.WriteAllTextAsync(content)
.ConfigureAwait(continueOnCapturedContext: false);
done = true;
}
catch (Exception ex)
{
lastErr = ex;
}
// If the file was not created, not written, or partially written,
// the events queue may be left with a file name that references a
// file that is nonexistent, empty, or invalid. It's easier to handle
// this when the queue is read than to try to dequeue the name.
if (attempts > 100)
throw new KeenException("Persistent failure while saving file, aborting", lastErr);
} while (!done);
}
public Task Add(CachedEvent e)
{
if (null == e)
throw new KeenException("Cached events may not be null");
return Task.Run(() =>
{
lock (events)
events.Enqueue(e);
});
}
public async Task<CachedEvent> TryTake()
{
var keenFolder = await getKeenFolder()
.ConfigureAwait(continueOnCapturedContext: false);
if (!events.Any())
return null;
string fileName;
lock(events)
fileName = events.Dequeue();
var file = await keenFolder.GetFileAsync(fileName)
.ConfigureAwait(continueOnCapturedContext: false);
var content = await file.ReadAllTextAsync()
.ConfigureAwait(continueOnCapturedContext: false);
var ce = JObject.Parse(content);
var item = new CachedEvent((string)ce.SelectToken("Collection"), (JObject)ce.SelectToken("Event"), ce.SelectToken("Error").ToObject<Exception>() );
await file.DeleteAsync()
.ConfigureAwait(continueOnCapturedContext: false);
return item;
}