mcs/class/corlib/System.Threading.Tasks/TaskScheduler.cs

   1 //
   2 // TaskScheduler.cs
   3 //
   4 // Authors:
   5 //       Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
   6 //       Marek Safar <marek.safar@gmail.com>
   7 //
   8 // Copyright (c) 2009 Jérémie "Garuma" Laval
   9 // Copyright 2012 Xamarin, Inc (http://www.xamarin.com)
  10 //
  11 // Permission is hereby granted, free of charge, to any person obtaining a copy
  12 // of this software and associated documentation files (the "Software"), to deal
  13 // in the Software without restriction, including without limitation the rights
  14 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  15 // copies of the Software, and to permit persons to whom the Software is
  16 // furnished to do so, subject to the following conditions:
  17 //
  18 // The above copyright notice and this permission notice shall be included in
  19 // all copies or substantial portions of the Software.
  20 //
  21 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  22 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  23 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  24 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  25 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  26 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  27 // THE SOFTWARE.
  28
  29 #if NET_4_0
  30
  31 using System.Collections.Generic;
  32 using System.Diagnostics;
  33
  34 namespace System.Threading.Tasks
  35 {
  36         [DebuggerDisplay ("Id={Id}")]
  37         [DebuggerTypeProxy (typeof (TaskSchedulerDebuggerView))]
  38         public abstract class TaskScheduler
  39         {
  40                 sealed class TaskSchedulerDebuggerView
  41                 {
  42                         readonly TaskScheduler scheduler;
  43
  44                         public TaskSchedulerDebuggerView (TaskScheduler scheduler)
  45                         {
  46                                 this.scheduler = scheduler;
  47                         }
  48
  49                         public IEnumerable<Task> ScheduledTasks {
  50                                 get {
  51                                         return scheduler.GetScheduledTasks ();
  52                                 }
  53                         }
  54                 }
  55
  56                 static readonly TaskScheduler defaultScheduler = new TpScheduler ();
  57
  58                 [ThreadStatic]
  59                 static TaskScheduler currentScheduler;
  60
  61                 int id;
  62                 static int lastId = int.MinValue;
  63
  64                 public static event EventHandler<UnobservedTaskExceptionEventArgs> UnobservedTaskException;
  65
  66                 protected TaskScheduler ()
  67                 {
  68                         this.id = Interlocked.Increment (ref lastId);
  69                 }
  70
  71                 public static TaskScheduler FromCurrentSynchronizationContext ()
  72                 {
  73                         var syncCtx = SynchronizationContext.Current;
  74                         if (syncCtx == null)
  75                                 throw new InvalidOperationException ("The current SynchronizationContext is null and cannot be used as a TaskScheduler");
  76
  77                         return new SynchronizationContextScheduler (syncCtx);
  78                 }
  79
  80                 public static TaskScheduler Default  {
  81                         get {
  82                                 return defaultScheduler;
  83                         }
  84                 }
  85
  86                 public static TaskScheduler Current  {
  87                         get {
  88                                 if (currentScheduler != null)
  89                                         return currentScheduler;
  90
  91                                 return defaultScheduler;
  92                         }
  93                         internal set {
  94                                 currentScheduler = value;
  95                         }
  96                 }
  97
  98                 public int Id {
  99                         get {
 100                                 return id;
 101                         }
 102                 }
 103
 104                 internal static bool IsDefault {
 105                         get {
 106                                 return currentScheduler == null || currentScheduler == defaultScheduler;
 107                         }
 108                 }
 109
 110                 public virtual int MaximumConcurrencyLevel {
 111                         get {
 112                                 return int.MaxValue;
 113                         }
 114                 }
 115
 116                 protected abstract IEnumerable<Task> GetScheduledTasks ();
 117                 protected internal abstract void QueueTask (Task task);
 118
 119                 protected internal virtual bool TryDequeue (Task task)
 120                 {
 121                         return false;
 122                 }
 123
 124                 internal protected bool TryExecuteTask (Task task)
 125                 {
 126                         if (task.IsCompleted)
 127                                 return false;
 128
 129                         if (task.Status == TaskStatus.WaitingToRun) {
 130                                 task.Execute ();
 131                                 if (task.WaitOnChildren ())
 132                                         task.Wait ();
 133
 134                                 return true;
 135                         }
 136
 137                         return false;
 138                 }
 139
 140                 protected abstract bool TryExecuteTaskInline (Task task, bool taskWasPreviouslyQueued);
 141
 142                 internal bool RunInline (Task task, bool taskWasPreviouslyQueued)
 143                 {
 144                         if (!TryExecuteTaskInline (task, taskWasPreviouslyQueued))
 145                                 return false;
 146
 147                         if (!task.IsCompleted)
 148                                 throw new InvalidOperationException ("The TryExecuteTaskInline call to the underlying scheduler succeeded, but the task body was not invoked");
 149
 150                         return true;
 151                 }
 152
 153                 internal static UnobservedTaskExceptionEventArgs FireUnobservedEvent (Task task, AggregateException e)
 154                 {
 155                         UnobservedTaskExceptionEventArgs args = new UnobservedTaskExceptionEventArgs (e);
 156
 157                         EventHandler<UnobservedTaskExceptionEventArgs> temp = UnobservedTaskException;
 158                         if (temp == null)
 159                                 return args;
 160
 161                         temp (task, args);
 162
 163                         return args;
 164                 }
 165         }
 166 }
 167 #endif