mcs/class/corlib/System.Threading/ThreadLocal.cs

   1 //
   2 // ThreadLocal.cs
   3 //
   4 // Author:
   5 //       Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
   6 //       Rewritten by Paolo Molaro (lupus@ximian.com)
   7 //
   8 // Copyright (c) 2009 Jérémie "Garuma" Laval
   9 //
  10 // Permission is hereby granted, free of charge, to any person obtaining a copy
  11 // of this software and associated documentation files (the "Software"), to deal
  12 // in the Software without restriction, including without limitation the rights
  13 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  14 // copies of the Software, and to permit persons to whom the Software is
  15 // furnished to do so, subject to the following conditions:
  16 //
  17 // The above copyright notice and this permission notice shall be included in
  18 // all copies or substantial portions of the Software.
  19 //
  20 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  21 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  22 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  23 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  24 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  25 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  26 // THE SOFTWARE.
  27
  28 using System;
  29 using System.Collections.Generic;
  30 using System.Runtime.Serialization;
  31 using System.Runtime.InteropServices;
  32 using System.Security.Permissions;
  33
  34 namespace System.Threading
  35 {
  36         [System.Diagnostics.DebuggerDisplay ("IsValueCreated={IsValueCreated}, Value={ValueForDebugDisplay}")]
  37         public class ThreadLocal<T> : IDisposable
  38         {
  39                 struct TlsDatum {
  40                         internal sbyte state; /* 0 uninitialized, < 0 initializing, > 0 inited */
  41                         internal Exception cachedException; /* this is per-thread */
  42                         internal T data;
  43                 }
  44
  45                 Func<T> valueFactory;
  46                 /* The tlsdata field is handled magically by the JIT
  47                  * It must be a struct and it is always accessed by ldflda: the JIT, instead of
  48                  * computing the address inside the instance, will return the address of the variable
  49                  * for the current thread (based on tls_offset). This magic wouldn't be needed if C#
  50                  * let us declare an icall with a TlsDatum& return type...
  51                  * For this same reason, we must check tls_offset for != 0 to make sure it's valid before accessing tlsdata
  52                  * The address of the tls var is cached per method at the first IL ldflda instruction, so care must be taken
  53                  * not to cause it to be conditionally executed.
  54                  */
  55                 uint tls_offset;
  56                 TlsDatum tlsdata;
  57
  58                 public ThreadLocal ()
  59                 {
  60                         tls_offset = Thread.AllocTlsData (typeof (TlsDatum));
  61                 }
  62
  63                 public ThreadLocal (Func<T> valueFactory) : this ()
  64                 {
  65                         if (valueFactory == null)
  66                                 throw new ArgumentNullException ("valueFactory");
  67                         this.valueFactory = valueFactory;
  68                 }
  69
  70                 public ThreadLocal (bool trackAllValues) : this () {
  71                         if (trackAllValues)
  72                                 throw new NotImplementedException ();
  73                 }
  74
  75                 public ThreadLocal (Func<T> valueFactory, bool trackAllValues) : this (valueFactory) {
  76                         if (trackAllValues)
  77                                 throw new NotImplementedException ();
  78                 }
  79
  80                 public void Dispose ()
  81                 {
  82                         Dispose (true);
  83                 }
  84
  85                 protected virtual void Dispose (bool disposing)
  86                 {
  87                         if (tls_offset != 0) {
  88                                 uint o = tls_offset;
  89                                 tls_offset = 0;
  90                                 if (disposing)
  91                                         valueFactory = null;
  92                                 Thread.DestroyTlsData (o);
  93                                 GC.SuppressFinalize (this);
  94                         }
  95                 }
  96
  97                 ~ThreadLocal ()
  98                 {
  99                         Dispose (false);
 100                 }
 101
 102                 public bool IsValueCreated {
 103                         get {
 104                                 if (tls_offset == 0)
 105                                         throw new ObjectDisposedException ("ThreadLocal object");
 106                                 /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 107                                 return tlsdata.state > 0;
 108                         }
 109                 }
 110
 111                 T GetSlowPath () {
 112                         /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 113                         if (tlsdata.cachedException != null)
 114                                 throw tlsdata.cachedException;
 115                         if (tlsdata.state < 0)
 116                                 throw new InvalidOperationException ("The initialization function attempted to reference Value recursively");
 117                         tlsdata.state = -1;
 118                         if (valueFactory != null) {
 119                                 try {
 120                                         tlsdata.data = valueFactory ();
 121                                 } catch (Exception ex) {
 122                                         tlsdata.cachedException = ex;
 123                                         throw ex;
 124                                 }
 125                         } else {
 126                                 tlsdata.data = default (T);
 127                         }
 128                         tlsdata.state = 1;
 129                         return tlsdata.data;
 130                 }
 131
 132                 [System.Diagnostics.DebuggerBrowsableAttribute (System.Diagnostics.DebuggerBrowsableState.Never)]
 133                 public T Value {
 134                         get {
 135                                 if (tls_offset == 0)
 136                                         throw new ObjectDisposedException ("ThreadLocal object");
 137                                 /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 138                                 if (tlsdata.state > 0)
 139                                         return tlsdata.data;
 140                                 return GetSlowPath ();
 141                         }
 142                         set {
 143                                 if (tls_offset == 0)
 144                                         throw new ObjectDisposedException ("ThreadLocal object");
 145                                 /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 146                                 tlsdata.state = 1;
 147                                 tlsdata.data = value;
 148                         }
 149                 }
 150
 151                 public IList<T> Values {
 152                         get {
 153                                 if (tls_offset == 0)
 154                                         throw new ObjectDisposedException ("ThreadLocal object");
 155                                 throw new NotImplementedException ();
 156                         }
 157                 }
 158
 159                 public override string ToString ()
 160                 {
 161                         return Value.ToString ();
 162                 }
 163
 164         }
 165 }