////////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   Selectable.cs
//
//  Note: File is part of Sing# runtime files and copied into Singularity tree
//        whenever a new version of Sing# is dropped.
//
using System;
#if ENDPOINT_STRUCT
using Microsoft.Singularity.V1.Threads;
#else
using System.Threading;
#endif
using Microsoft.SingSharp;

namespace Microsoft.Singularity.Channels {

    [AttributeUsage(AttributeTargets.Method)]
    public class SelectableAttribute : Attribute {
      public SelectableAttribute(int tag) {}
    }
    
    
    [CLSCompliant(false)]
    public interface ISelectable : IBorrowed {

        /// <summary>
        /// Tests if the message at the head of the queue matches the given tag. If so,
        /// returns true.
        ///
        /// If no match is possible in the future given the current message, possible must
        /// be set to false. 
        /// Implementations are disallowed from setting possible to true
        /// so that the context can chain them.
        ///
        /// If the underlying object is an endpoint set, it also returns an object that
        /// serves to extract the endpoint having the match from the set later.
        ///
        /// Again, implementations are disallowed from setting match setMatch to null
        /// so that the context can chain the calls.
        ///
        /// </summary>
        bool HeadMatches(int tag, ref bool possible, ref object setMatch);
        
        /// <summary>
        /// Allow the context to get a handle to wait on an event for this object
        /// </summary>
        #if ENDPOINT_STRUCT
        SyncHandle GetWaitHandle();
        #else
        WaitHandle GetWaitHandle();
        #endif

        /// <summary>
        /// Reset the associated event to avoid spurious wake-ups. This is called by
        /// Select prior to scanning the state of the ISelectable object.
        /// </summary>
        void ResetWaitSignal();
    }


    [CLSCompliant(false)]
    public interface IEventCollectionElement : ISelectable, ITracked {

        /// <summary>
        /// Instruct the selectable object to signal events on the given AutoResetEvent
        /// rather than its normal event in order to aggregate signalling into a set.
        /// A selectable object need only support being part of a single collection at
        /// any point in time.
        /// </summary>
        #if ENDPOINT_STRUCT
        void LinkIntoCollection(AutoResetEventHandle ev);
        #else
        void LinkIntoCollection(AutoResetEvent ev);
        #endif

        /// <summary>
        /// Instruct the selectable object to stop signalling events on the given
        /// AutoResetEvent.
        /// </summary>
        #if ENDPOINT_STRUCT
        void UnlinkFromCollection(AutoResetEventHandle ev);
        #else
        void UnlinkFromCollection(AutoResetEvent ev);
        #endif
    }
}