AsyncCallBase.cs

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#endregion

using System;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using Grpc.Core.Internal;
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>
    {
        readonly Func<TWrite, byte[]> serializer;
        readonly Func<byte[], TRead> deserializer;

        protected readonly object myLock = new object();

        protected CallSafeHandle call;
        protected bool disposed;

        protected bool started;
        protected bool errorOccured;
        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;
        protected bool halfcloseRequested;
        protected bool halfclosed;
        protected bool finished;  // True if close has been received from the peer.

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

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

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

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

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

        protected void InitializeInternal(CallSafeHandle 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, AsyncCompletionDelegate<object> completionDelegate)
        {
            byte[] payload = UnsafeSerialize(msg);

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

                call.StartSendMessage(payload, HandleSendFinished);
                sendCompletionDelegate = completionDelegate;
            }
        }

        /// <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)
            {
                Preconditions.CheckNotNull(completionDelegate, "Completion delegate cannot be null");
                CheckReadingAllowed();

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

        // TODO(jtattermusch): find more fitting name for this method.
        /// <summary>
        /// Default behavior just completes the read observer, but more sofisticated behavior might be required
        /// by subclasses.
        /// </summary>
        protected virtual void ProcessLastRead(AsyncCompletionDelegate<TRead> completionDelegate)
        {
            FireCompletion(completionDelegate, default(TRead), null);
        }

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

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

        protected virtual void OnReleaseResources()
        {
        }

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

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

        protected void CheckReadingAllowed()
        {
            Preconditions.CheckState(started);
            Preconditions.CheckState(!disposed);
            Preconditions.CheckState(!errorOccured);

            Preconditions.CheckState(!readingDone, "Stream has already been closed.");
            Preconditions.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)
        {
            return serializer(msg);
        }

        protected bool TrySerialize(TWrite msg, out byte[] payload)
        {
            try
            {
                payload = serializer(msg);
                return true;
            }
            catch (Exception)
            {
                Console.WriteLine("Exception occured while trying to serialize message");
                payload = null;
                return false;
            }
        }

        protected bool TryDeserialize(byte[] payload, out TRead msg)
        {
            try
            {
                msg = deserializer(payload);
                return true;
            } 
            catch (Exception)
            {
                Console.WriteLine("Exception occured while trying to deserialize message");
                msg = default(TRead);
                return false;
            }
        }

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

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

                ReleaseResourcesIfPossible();
            }

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

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

                ReleaseResourcesIfPossible();
            }

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

        /// <summary>
        /// Handles streaming read completion.
        /// </summary>
        protected void HandleReadFinished(bool success, BatchContextSafeHandle ctx)
        {
            var payload = ctx.GetReceivedMessage();

            AsyncCompletionDelegate<TRead> origCompletionDelegate = null;
            lock (myLock)
            {
                origCompletionDelegate = readCompletionDelegate;
                if (payload != null)
                {
                    readCompletionDelegate = null;
                }
                else
                {
                    // This was the last read. Keeping the readCompletionDelegate
                    // to be either fired by this handler or by client-side finished
                    // handler.
                    readingDone = true;
                }

                ReleaseResourcesIfPossible();
            }

            // TODO: handle the case when error occured...

            if (payload != null)
            {
                // TODO: handle deserialization error
                TRead msg;
                TryDeserialize(payload, out msg);

                FireCompletion(origCompletionDelegate, msg, null);
            }
            else
            {
                ProcessLastRead(origCompletionDelegate);
            }
        }
    }
}