/// <summary>
/// Tries to enqueue the given async write and callback
/// </summary>
/// <param name="w"></param>
/// <param name="writerDelegate"></param>
/// <returns></returns>
public AsyncQueueResult Queue(AsyncWrite w, Func <AsyncWrite, Task> writerDelegate)
{
lock (sync) {
if (GetQueuedBufferBytes() + w.GetBufferLength() > MaxQueueBytes)
{
return(AsyncQueueResult.QueueFull); //Because we would use too much ram.
}
if (c.ContainsKey(w.Key))
{
return(AsyncQueueResult.AlreadyPresent); //We already have a queued write for this data.
}
c.Add(w.Key, w);
Task.Run(
async() => {
try
{
await writerDelegate(w);
}
finally
{
Remove(w);
}
}).ConfigureAwait(false);
return(AsyncQueueResult.Enqueued);
}
}
/// <summary>
/// Returns false when (a) the specified AsyncWrite value already exists, (b) the queue is full, or (c) the thread pool queue is full
/// </summary>
/// <param name="w"></param>
/// <param name="writerDelegate"></param>
/// <returns></returns>
public bool Queue(AsyncWrite w, WriterDelegate writerDelegate)
{
lock (_sync) {
if (GetQueuedBufferBytes() + w.GetBufferLength() > MaxQueueBytes)
{
return(false); //Because we would use too much ram.
}
if (c.ContainsKey(w.Key))
{
return(false); //We already have a queued write for this data.
}
c.Add(w.Key, w);
Task.Run(
async() => {
await writerDelegate(w);
Remove(w);
}).ConfigureAwait(false);
return(true);
}
}
/// <summary>
/// Removes the specified object based on its relativepath and modifieddateutc values.
/// </summary>
/// <param name="w"></param>
public void Remove(AsyncWrite w)
{
lock (_sync) {
c.Remove(w.Key);
}
}
/// <summary>
/// May return either a physical file name or a MemoryStream with the data.
/// Writes are (usually) asynchronous. If the write queue is full, the write is forced to be synchronous again.
/// Identical to GetCachedFile() when asynchronous=false
/// </summary>
/// <param name="keyBasis"></param>
/// <param name="extension"></param>
/// <param name="writeCallback"></param>
/// <param name="timeoutMs"></param>
/// <param name="asynchronous"></param>
/// <returns></returns>
public async Task <CacheResult> GetCachedFile(string keyBasis, string extension, AsyncWriteResult writeCallback, int timeoutMs, bool asynchronous)
{
Stopwatch sw = null;
if (logger != null)
{
sw = Stopwatch.StartNew();
}
//Relative to the cache directory. Not relative to the app or domain root
var keyBasisBytes = new UTF8Encoding().GetBytes(keyBasis);
var relativePath = new HashBasedPathBuilder().BuildPath(keyBasisBytes, subfolders, "/") + '.' + extension;
//Physical path
var physicalPath = PhysicalCachePath.TrimEnd('\\', '/') + Path.DirectorySeparatorChar +
relativePath.Replace('/', Path.DirectorySeparatorChar);
var result = new CacheResult(CacheQueryResult.Hit, physicalPath, relativePath);
var asyncFailed = false;
//2013-apr-25: What happens if the file is still being written to disk - it's present but not complete? To handle that, we use mayBeLocked.
var mayBeLocked = Locks.MayBeLocked(relativePath.ToUpperInvariant());
//On the first check, verify the file exists using System.IO directly (the last 'true' parameter).
if (!asynchronous)
{
//On the first check, verify the file exists using System.IO directly (the last 'true' parameter)
//May throw an IOException if the file cannot be opened, and is locked by an external processes for longer than timeoutMs.
//This method may take longer than timeoutMs under absolute worst conditions.
if (!await TryWriteFile(result, physicalPath, relativePath, writeCallback, timeoutMs, !mayBeLocked))
{
//On failure
result.Result = CacheQueryResult.Failed;
}
}
else if (!Index.ExistsCertain(relativePath, physicalPath) || mayBeLocked)
{
//Looks like a miss. Let's enter a lock for the creation of the file. This is a different locking system than for writing to the file - far less contention, as it doesn't include the
//This prevents two identical requests from duplicating efforts. Different requests don't lock.
//Lock execution using relativePath as the sync basis. Ignore casing differences. This prevents duplicate entries in the write queue and wasted CPU/RAM usage.
if (!await QueueLocks.TryExecuteAsync(relativePath.ToUpperInvariant(), timeoutMs, CancellationToken.None,
async() => {
//Now, if the item we seek is in the queue, we have a memcached hit. If not, we should check the index. It's possible the item has been written to disk already.
//If both are a miss, we should see if there is enough room in the write queue. If not, switch to in-thread writing.
AsyncWrite t = CurrentWrites.Get(relativePath);
if (t != null)
{
result.Data = t.GetReadonlyStream();
}
//On the second check, use cached data for speed. The cached data should be updated if another thread updated a file (but not if another process did).
//When t == null, and we're inside QueueLocks, all work on the file must be finished, so we have no need to consult mayBeLocked.
if (t == null && !Index.Exists(relativePath, physicalPath))
{
result.Result = CacheQueryResult.Miss;
//Still a miss, we even rechecked the file system. Write to memory.
MemoryStream ms = new MemoryStream(4096); //4K initial capacity is minimal, but this array will get copied around a lot, better to underestimate.
//Read, resize, process, and encode the image. Lots of exceptions thrown here.
await writeCallback(ms);
ms.Position = 0;
AsyncWrite w = new AsyncWrite(ms, physicalPath, relativePath);
var queueResult = CurrentWrites.Queue(w, async delegate(AsyncWrite job)
{
try
{
var swIo = Stopwatch.StartNew();
//We want this to run synchronously, since it's in a background thread already.
if (!(await TryWriteFile(null, job.PhysicalPath, job.Key,
delegate(Stream s)
{
var fromStream = job.GetReadonlyStream();
return(fromStream.CopyToAsync(s));
}, timeoutMs, true)))
{
swIo.Stop();
//We failed to lock the file.
logger?.LogWarning(
"Failed to flush async write, timeout exceeded after {0}ms - {1}",
swIo.ElapsedMilliseconds, result.RelativePath);
}
else
{
swIo.Stop();
logger?.LogTrace("{0}ms: Async write started {1}ms after enqueue for {2}",
swIo.ElapsedMilliseconds.ToString().PadLeft(4),
DateTime.UtcNow.Subtract(w.JobCreatedAt).Subtract(swIo.Elapsed)
.TotalMilliseconds, result.RelativePath);
}
}
catch (Exception ex)
{
logger?.LogError("Failed to flush async write, {0} {1}\n{2}", ex.ToString(),
result.RelativePath, ex.StackTrace);
}
finally
{
CurrentWrites.Remove(job); //Remove from the queue, it's done or failed.
}
});
if (queueResult == AsyncWriteCollection.AsyncQueueResult.Enqueued ||
queueResult == AsyncWriteCollection.AsyncQueueResult.AlreadyPresent)
{
//We queued it! Send back a read-only memory stream
result.Data = w.GetReadonlyStream();
}
else
{
asyncFailed = false;
//We failed to queue it - either the ThreadPool was exhausted or we exceeded the MB limit for the write queue.
//Write the MemoryStream to disk using the normal method.
//This is nested inside a queueLock because if we failed here, the next one will also. Better to force it to wait until the file is written to disk.
if (!await TryWriteFile(result, physicalPath, relativePath, async delegate(Stream s) { await ms.CopyToAsync(s); }, timeoutMs, false))
{
logger?.LogWarning("Failed to queue async write, also failed to lock for sync writing: {0}", result.RelativePath);
}
}
}
}))
{
//On failure
result.Result = CacheQueryResult.Failed;
}
}
if (logger != null)
{
sw?.Stop();
logger?.LogTrace("{0}ms: {1}{2} for {3}, Key: {4}",
sw?.ElapsedMilliseconds.ToString(NumberFormatInfo.InvariantInfo).PadLeft(4),
asynchronous ? (asyncFailed ? "AsyncHttpMode, fell back to sync write " : "AsyncHttpMode+AsyncWrites ") : "AsyncHttpMode",
result.Result.ToString(),
result.RelativePath,
keyBasis);
}
//Fire event
CacheResultReturned?.Invoke(this, result);
return(result);
}