src/csharp/Grpc.Core/Internal/AsyncCallBase.cs

#region Copyright notice and license

// Copyright 2015-2016, Google Inc.
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// modification, are permitted provided that the following conditions are
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// 
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// copyright notice, this list of conditions and the following disclaimer
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// distribution.
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#endregion

using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;

using Grpc.Core.Internal;
using Grpc.Core.Logging;
using Grpc.Core.Profiling;
using Grpc.Core.Utils;

namespace Grpc.Core.Internal
{
    /// <summary>
    /// Base for handling both client side and server side calls.
    /// Manages native call lifecycle and provides convenience methods.
    /// </summary>
    internal abstract class AsyncCallBase<TWrite, TRead>
    {
        static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<AsyncCallBase<TWrite, TRead>>();
        protected static readonly Status DeserializeResponseFailureStatus = new Status(StatusCode.Internal, "Failed to deserialize response message.");

        readonly Func<TWrite, byte[]> serializer;
        readonly Func<byte[], TRead> deserializer;

        protected readonly GrpcEnvironment environment;
        protected readonly object myLock = new object();

        protected INativeCall call;
        protected bool disposed;

        protected bool started;
        protected bool cancelRequested;

        protected AsyncCompletionDelegate<object> sendCompletionDelegate;  // Completion of a pending send or sendclose if not null.
        protected AsyncCompletionDelegate<TRead> readCompletionDelegate;  // Completion of a pending send or sendclose if not null.

        protected bool readingDone;  // True if last read (i.e. read with null payload) was already received.
        protected bool halfcloseRequested;  // True if send close have been initiated.
        protected bool finished;  // True if close has been received from the peer.

        protected bool initialMetadataSent;
        protected long streamingWritesCounter;  // Number of streaming send operations started so far.

        public AsyncCallBase(Func<TWrite, byte[]> serializer, Func<byte[], TRead> deserializer, GrpcEnvironment environment)
        {
            this.serializer = GrpcPreconditions.CheckNotNull(serializer);
            this.deserializer = GrpcPreconditions.CheckNotNull(deserializer);
            this.environment = GrpcPreconditions.CheckNotNull(environment);
        }

        /// <summary>
        /// Requests cancelling the call.
        /// </summary>
        public void Cancel()
        {
            lock (myLock)
            {
                GrpcPreconditions.CheckState(started);
                cancelRequested = true;

                if (!disposed)
                {
                    call.Cancel();
                }
            }
        }

        /// <summary>
        /// Requests cancelling the call with given status.
        /// </summary>
        protected void CancelWithStatus(Status status)
        {
            lock (myLock)
            {
                cancelRequested = true;

                if (!disposed)
                {
                    call.CancelWithStatus(status);
                }
            }
        }

        protected void InitializeInternal(INativeCall call)
        {
            lock (myLock)
            {
                this.call = call;
            }
        }

        /// <summary>
        /// Initiates sending a message. Only one send operation can be active at a time.
        /// completionDelegate is invoked upon completion.
        /// </summary>
        protected void StartSendMessageInternal(TWrite msg, WriteFlags writeFlags, AsyncCompletionDelegate<object> completionDelegate)
        {
            byte[] payload = UnsafeSerialize(msg);

            lock (myLock)
            {
                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                CheckSendingAllowed();

                call.StartSendMessage(HandleSendFinished, payload, writeFlags, !initialMetadataSent);

                sendCompletionDelegate = completionDelegate;
                initialMetadataSent = true;
                streamingWritesCounter++;
            }
        }

        /// <summary>
        /// Initiates reading a message. Only one read operation can be active at a time.
        /// completionDelegate is invoked upon completion.
        /// </summary>
        protected void StartReadMessageInternal(AsyncCompletionDelegate<TRead> completionDelegate)
        {
            lock (myLock)
            {
                GrpcPreconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                CheckReadingAllowed();

                call.StartReceiveMessage(HandleReadFinished);
                readCompletionDelegate = completionDelegate;
            }
        }

        /// <summary>
        /// If there are no more pending actions and no new actions can be started, releases
        /// the underlying native resources.
        /// </summary>
        protected bool ReleaseResourcesIfPossible()
        {
            using (Profilers.ForCurrentThread().NewScope("AsyncCallBase.ReleaseResourcesIfPossible"))
            {
                if (!disposed && call != null)
                {
                    bool noMoreSendCompletions = sendCompletionDelegate == null && (halfcloseRequested || cancelRequested || finished);
                    if (noMoreSendCompletions && readingDone && finished)
                    {
                        ReleaseResources();
                        return true;
                    }
                }
                return false;
            }
        }

        protected abstract bool IsClient
        {
            get;
        }

        private void ReleaseResources()
        {
            if (call != null)
            {
                call.Dispose();
            }
            disposed = true;
            OnAfterReleaseResources();
        }

        protected virtual void OnAfterReleaseResources()
        {
        }

        protected void CheckSendingAllowed()
        {
            GrpcPreconditions.CheckState(started);
            CheckNotCancelled();
            GrpcPreconditions.CheckState(!disposed);

            GrpcPreconditions.CheckState(!halfcloseRequested, "Already halfclosed.");
            GrpcPreconditions.CheckState(!finished, "Already finished.");
            GrpcPreconditions.CheckState(sendCompletionDelegate == null, "Only one write can be pending at a time");
        }

        protected virtual void CheckReadingAllowed()
        {
            GrpcPreconditions.CheckState(started);
            GrpcPreconditions.CheckState(!disposed);

            GrpcPreconditions.CheckState(!readingDone, "Stream has already been closed.");
            GrpcPreconditions.CheckState(readCompletionDelegate == null, "Only one read can be pending at a time");
        }

        protected void CheckNotCancelled()
        {
            if (cancelRequested)
            {
                throw new OperationCanceledException("Remote call has been cancelled.");
            }
        }

        protected byte[] UnsafeSerialize(TWrite msg)
        {
            using (Profilers.ForCurrentThread().NewScope("AsyncCallBase.UnsafeSerialize"))
            {
                return serializer(msg);
            }
        }

        protected Exception TryDeserialize(byte[] payload, out TRead msg)
        {
            using (Profilers.ForCurrentThread().NewScope("AsyncCallBase.TryDeserialize"))
            {
                try
                {
                
                    msg = deserializer(payload);
                    return null;
             
                }
                catch (Exception e)
                {
                    msg = default(TRead);
                    return e;
                }
            }
        }

        protected void FireCompletion<T>(AsyncCompletionDelegate<T> completionDelegate, T value, Exception error)
        {
            try
            {
                completionDelegate(value, error);
            }
            catch (Exception e)
            {
                Logger.Error(e, "Exception occured while invoking completion delegate.");
            }
        }

        /// <summary>
        /// Handles send completion.
        /// </summary>
        protected void HandleSendFinished(bool success)
        {
            AsyncCompletionDelegate<object> origCompletionDelegate = null;
            lock (myLock)
            {
                origCompletionDelegate = sendCompletionDelegate;
                sendCompletionDelegate = null;

                ReleaseResourcesIfPossible();
            }

            if (!success)
            {
                FireCompletion(origCompletionDelegate, null, new InvalidOperationException("Send failed"));
            }
            else
            {
                FireCompletion(origCompletionDelegate, null, null);
            }
        }

        /// <summary>
        /// Handles halfclose completion.
        /// </summary>
        protected void HandleHalfclosed(bool success)
        {
            AsyncCompletionDelegate<object> origCompletionDelegate = null;
            lock (myLock)
            {
                origCompletionDelegate = sendCompletionDelegate;
                sendCompletionDelegate = null;

                ReleaseResourcesIfPossible();
            }

            if (!success)
            {
                FireCompletion(origCompletionDelegate, null, new InvalidOperationException("Halfclose failed"));
            }
            else
            {
                FireCompletion(origCompletionDelegate, null, null);
            }
        }

        /// <summary>
        /// Handles streaming read completion.
        /// </summary>
        protected void HandleReadFinished(bool success, byte[] receivedMessage)
        {
            TRead msg = default(TRead);
            var deserializeException = (success && receivedMessage != null) ? TryDeserialize(receivedMessage, out msg) : null;

            AsyncCompletionDelegate<TRead> origCompletionDelegate = null;
            lock (myLock)
            {
                origCompletionDelegate = readCompletionDelegate;
                readCompletionDelegate = null;

                if (receivedMessage == null)
                {
                    // This was the last read.
                    readingDone = true;
                }

                if (deserializeException != null && IsClient)
                {
                    readingDone = true;
                    CancelWithStatus(DeserializeResponseFailureStatus);
                }

                ReleaseResourcesIfPossible();
            }

            // TODO: handle the case when success==false

            if (deserializeException != null && !IsClient)
            {
                FireCompletion(origCompletionDelegate, default(TRead), new IOException("Failed to deserialize request message.", deserializeException));
                return;
            }
            FireCompletion(origCompletionDelegate, msg, null);
        }
    }
}