////////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   TRef.cs
//
//  Note: File is part of Sing# runtime files and copied into Singularity tree
//        whenever a new version of Sing# is dropped.
//        Coordinate any changes with Sing# team.
//

using System;
using Microsoft.SingSharp;
using Microsoft.Singularity.Memory;

namespace Microsoft.Singularity.Channels
{
  using System.Threading;
  using Allocation = Microsoft.Singularity.Memory.SharedHeap.Allocation;

  /// <summary>
  /// In order to capture the state of an endpoint when stored in a TRef, we
  /// need to attach the state to the type itself, because instance types cannot have attributes.
  ///
  /// We use opt modifier types for this.
  ///
  /// The syntax is TRef&lt; C.Imp @(State) &gt;
  /// </summary>
  public sealed class TRef<T,State> where T : unmanaged struct, ITracked
  {
    unsafe T* opt(ExHeap) opt(State) obj;
    Mutex! mutex;

    public TRef([Claims] T* opt(ExHeap) opt(State)! i_obj)
    {
      if (i_obj == null) {
        throw new ArgumentNullException("TRef must be initialized with a non-null value!");
      }
      i_obj->Release();
#if SINGULARITY_KERNEL
      // In the Kernel, TRefs are used sometimes to pass endpoints between threads
      // of different processes. So we have to set it to the kernel on release.
      unsafe {
          Process kernelProcess = Process.KernelProcess;
          Process currentProcess = Thread.CurrentProcess;
          if ((kernelProcess != null) && (currentProcess != null)) {
              i_obj = (T* opt(ExHeap) opt(State)!)EndpointCore.MoveEndpoint(
                  currentProcess.ProcessSharedHeap, SharedHeap.KernelSharedHeap,
                  kernelProcess, (Allocation*)i_obj);
          }
      }
#endif
      obj = i_obj;
      this.mutex = new Mutex();
    }

    // invariant:
    //   If mutex is held, thread holding mutex is responsible for calling Release
    //   during that time, the obj slot is empty and if the thread tries to acquire it
    //   again, an exception is thrown.

    /// <summary>
    /// Will block until the TRef is free.
    /// </summary>
    /// <returns>Acquired tracked type protected by TRef</returns>
    public T* opt(ExHeap) opt(State)! Acquire()
    {
      this.mutex.WaitOne();
      T* opt(ExHeap) opt(State) elem = this.obj;
      if (elem == null) {
        throw new ApplicationException("thread already holds TRef!");
      }
#if SINGULARITY_KERNEL
      // In the Kernel, TRefs are used sometimes to pass endpoints between threads
      // of different processes. So we have to set the new owner correctly.
      unsafe {
          Process currentProcess = Thread.CurrentProcess;
          if (currentProcess != null) {
              elem = (T* opt(ExHeap) opt(State)!)EndpointCore.MoveEndpoint(
                  SharedHeap.KernelSharedHeap, currentProcess.ProcessSharedHeap,
                  currentProcess, (Allocation*)elem);
          }
      }
#endif
      elem->Acquire();
      this.obj = null;
      return elem;
    }

    /// <summary>
    /// Releases tracked data into the TRef so other threads can access it.
    /// </summary>
    /// <param name="newObj">tracked data to be released</param>
    public void Release([Claims] T* opt(ExHeap) opt(State)! newObj)
    {
      if (newObj == null) {
        throw new ArgumentNullException("TRef must be released with a non-null value!");
      }
      newObj->Release();
#if SINGULARITY_KERNEL
      // In the Kernel, TRefs are used sometimes to pass endpoints between threads
      // of different processes. So we have to set it to the kernel on release.
      unsafe {
          Process kernelProcess = Process.KernelProcess;
          Process currentProcess = Thread.CurrentProcess;
          if ((kernelProcess != null) && (currentProcess != null)) {
              newObj = (T* opt(ExHeap) opt(State)!)EndpointCore.MoveEndpoint(
                  currentProcess.ProcessSharedHeap, SharedHeap.KernelSharedHeap,
                  kernelProcess, (Allocation*)newObj);
          }
      }
#endif
      obj = newObj;
      this.mutex.ReleaseMutex();
    }

    /// <summary>
    /// Finalizer to dispose of any left over contents
    /// </summary>
    ~TRef() {
      T* opt(ExHeap) opt(State) toDelete = this.obj;
      if (toDelete != null) {
        this.obj = null;
        unsafe {
#if SINGULARITY_KERNEL
          Tracing.Log(Tracing.Audit, "TRef finalizing {0:x}", (UIntPtr)toDelete);
#endif
          toDelete->Dispose(); // Explicit call needed due to generics
        }
        delete toDelete;
      }
    }

  }
}