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 #if NET_4_0
  29 using System;
  30 using System.Collections.Generic;
  31 using System.Runtime.Serialization;
  32 using System.Runtime.InteropServices;
  33 using System.Security.Permissions;
  34
  35 namespace System.Threading
  36 {
  37         [System.Diagnostics.DebuggerDisplay ("IsValueCreated={IsValueCreated}, Value={ValueForDebugDisplay}")]
  38         public class ThreadLocal<T> : IDisposable
  39         {
  40                 struct TlsDatum {
  41                         internal sbyte state; /* 0 uninitialized, < 0 initializing, > 0 inited */
  42                         internal Exception cachedException; /* this is per-thread */
  43                         internal T data;
  44                 }
  45
  46                 Func<T> valueFactory;
  47                 /* The tlsdata field is handled magically by the JIT
  48                  * It must be a struct and it is always accessed by ldflda: the JIT, instead of
  49                  * computing the address inside the instance, will return the address of the variable
  50                  * for the current thread (based on tls_offset). This magic wouldn't be needed if C#
  51                  * let us declare an icall with a TlsDatum& return type...
  52                  * For this same reason, we must check tls_offset for != 0 to make sure it's valid before accessing tlsdata
  53                  * The address of the tls var is cached per method at the first IL ldflda instruction, so care must be taken
  54                  * not to cause it to be conditionally executed.
  55                  */
  56                 uint tls_offset;
  57                 TlsDatum tlsdata;
  58
  59                 public ThreadLocal ()
  60                 {
  61                         tls_offset = Thread.AllocTlsData (typeof (TlsDatum));
  62                 }
  63
  64                 public ThreadLocal (Func<T> valueFactory) : this ()
  65                 {
  66                         if (valueFactory == null)
  67                                 throw new ArgumentNullException ("valueFactory");
  68                         this.valueFactory = valueFactory;
  69                 }
  70
  71 #if NET_4_5
  72                 public ThreadLocal (bool trackAllValues) : this () {
  73                         if (trackAllValues)
  74                                 throw new NotImplementedException ();
  75                 }
  76
  77                 public ThreadLocal (Func<T> valueFactory, bool trackAllValues) : this (valueFactory) {
  78                         if (trackAllValues)
  79                                 throw new NotImplementedException ();
  80                 }
  81 #endif
  82
  83                 public void Dispose ()
  84                 {
  85                         Dispose (true);
  86                 }
  87
  88                 protected virtual void Dispose (bool disposing)
  89                 {
  90                         if (tls_offset != 0) {
  91                                 uint o = tls_offset;
  92                                 tls_offset = 0;
  93                                 if (disposing)
  94                                         valueFactory = null;
  95                                 Thread.DestroyTlsData (o);
  96                                 GC.SuppressFinalize (this);
  97                         }
  98                 }
  99
 100                 ~ThreadLocal ()
 101                 {
 102                         Dispose (false);
 103                 }
 104
 105                 public bool IsValueCreated {
 106                         get {
 107                                 if (tls_offset == 0)
 108                                         throw new ObjectDisposedException ("ThreadLocal object");
 109                                 /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 110                                 return tlsdata.state > 0;
 111                         }
 112                 }
 113
 114                 T GetSlowPath () {
 115                         /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 116                         if (tlsdata.cachedException != null)
 117                                 throw tlsdata.cachedException;
 118                         if (tlsdata.state < 0)
 119                                 throw new InvalidOperationException ("The initialization function attempted to reference Value recursively");
 120                         tlsdata.state = -1;
 121                         if (valueFactory != null) {
 122                                 try {
 123                                         tlsdata.data = valueFactory ();
 124                                 } catch (Exception ex) {
 125                                         tlsdata.cachedException = ex;
 126                                         throw ex;
 127                                 }
 128                         } else {
 129                                 tlsdata.data = default (T);
 130                         }
 131                         tlsdata.state = 1;
 132                         return tlsdata.data;
 133                 }
 134
 135                 [System.Diagnostics.DebuggerBrowsableAttribute (System.Diagnostics.DebuggerBrowsableState.Never)]
 136                 public T Value {
 137                         get {
 138                                 if (tls_offset == 0)
 139                                         throw new ObjectDisposedException ("ThreadLocal object");
 140                                 /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 141                                 if (tlsdata.state > 0)
 142                                         return tlsdata.data;
 143                                 return GetSlowPath ();
 144                         }
 145                         set {
 146                                 if (tls_offset == 0)
 147                                         throw new ObjectDisposedException ("ThreadLocal object");
 148                                 /* ALERT! magic tlsdata JIT access redirects to TLS value instead of instance field */
 149                                 tlsdata.state = 1;
 150                                 tlsdata.data = value;
 151                         }
 152                 }
 153
 154 #if NET_4_5
 155                 public IList<T> Values {
 156                         get {
 157                                 if (tls_offset == 0)
 158                                         throw new ObjectDisposedException ("ThreadLocal object");
 159                                 throw new NotImplementedException ();
 160                         }
 161                 }
 162 #endif
 163
 164                 public override string ToString ()
 165                 {
 166                         return Value.ToString ();
 167                 }
 168
 169         }
 170 }
 171 #endif