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
  30 using System.Collections.Generic;
  31 using System.Diagnostics;
  32
  33 namespace System.Threading.Tasks
  34 {
  35         [DebuggerDisplay ("Id={Id}")]
  36         [DebuggerTypeProxy (typeof (TaskSchedulerDebuggerView))]
  37         public abstract class TaskScheduler
  38         {
  39                 sealed class TaskSchedulerDebuggerView
  40                 {
  41                         readonly TaskScheduler scheduler;
  42
  43                         public TaskSchedulerDebuggerView (TaskScheduler scheduler)
  44                         {
  45                                 this.scheduler = scheduler;
  46                         }
  47
  48                         public IEnumerable<Task> ScheduledTasks {
  49                                 get {
  50                                         return scheduler.GetScheduledTasks ();
  51                                 }
  52                         }
  53                 }
  54
  55                 static readonly TaskScheduler defaultScheduler = new TpScheduler ();
  56
  57                 [ThreadStatic]
  58                 static TaskScheduler currentScheduler;
  59
  60                 int id;
  61                 static int lastId = int.MinValue;
  62
  63                 public static event EventHandler<UnobservedTaskExceptionEventArgs> UnobservedTaskException;
  64
  65                 protected TaskScheduler ()
  66                 {
  67                         this.id = Interlocked.Increment (ref lastId);
  68                 }
  69
  70                 public static TaskScheduler FromCurrentSynchronizationContext ()
  71                 {
  72                         var syncCtx = SynchronizationContext.Current;
  73                         if (syncCtx == null)
  74                                 throw new InvalidOperationException ("The current SynchronizationContext is null and cannot be used as a TaskScheduler");
  75
  76                         return new SynchronizationContextScheduler (syncCtx);
  77                 }
  78
  79                 public static TaskScheduler Default  {
  80                         get {
  81                                 return defaultScheduler;
  82                         }
  83                 }
  84
  85                 public static TaskScheduler Current  {
  86                         get {
  87                                 if (currentScheduler != null)
  88                                         return currentScheduler;
  89
  90                                 return defaultScheduler;
  91                         }
  92                         internal set {
  93                                 currentScheduler = value;
  94                         }
  95                 }
  96
  97                 public int Id {
  98                         get {
  99                                 return id;
 100                         }
 101                 }
 102
 103                 internal static bool IsDefault {
 104                         get {
 105                                 return currentScheduler == null || currentScheduler == defaultScheduler;
 106                         }
 107                 }
 108
 109                 public virtual int MaximumConcurrencyLevel {
 110                         get {
 111                                 return int.MaxValue;
 112                         }
 113                 }
 114
 115                 protected abstract IEnumerable<Task> GetScheduledTasks ();
 116                 protected internal abstract void QueueTask (Task task);
 117
 118                 protected internal virtual bool TryDequeue (Task task)
 119                 {
 120                         return false;
 121                 }
 122
 123                 internal protected bool TryExecuteTask (Task task)
 124                 {
 125                         if (task.IsCompleted)
 126                                 return false;
 127
 128                         if (task.Status == TaskStatus.WaitingToRun) {
 129                                 task.Execute ();
 130                                 if (task.WaitOnChildren ())
 131                                         task.Wait ();
 132
 133                                 return true;
 134                         }
 135
 136                         return false;
 137                 }
 138
 139                 protected abstract bool TryExecuteTaskInline (Task task, bool taskWasPreviouslyQueued);
 140
 141                 internal bool RunInline (Task task, bool taskWasPreviouslyQueued)
 142                 {
 143                         if (!TryExecuteTaskInline (task, taskWasPreviouslyQueued))
 144                                 return false;
 145
 146                         if (!task.IsCompleted)
 147                                 throw new InvalidOperationException ("The TryExecuteTaskInline call to the underlying scheduler succeeded, but the task body was not invoked");
 148
 149                         return true;
 150                 }
 151
 152                 internal static UnobservedTaskExceptionEventArgs FireUnobservedEvent (Task task, AggregateException e)
 153                 {
 154                         UnobservedTaskExceptionEventArgs args = new UnobservedTaskExceptionEventArgs (e);
 155
 156                         EventHandler<UnobservedTaskExceptionEventArgs> temp = UnobservedTaskException;
 157                         if (temp == null)
 158                                 return args;
 159
 160                         temp (task, args);
 161
 162                         return args;
 163                 }
 164         }
 165 }