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