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Resource.d

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00001 /*******************************************************************************
00002 
00003         @file Resource.d
00004         
00005         Copyright (C) 2004 Kris Bell
00006         
00007         This software is provided 'as-is', without any express or implied
00008         warranty. In no event will the authors be held liable for damages
00009         of any kind arising from the use of this software.
00010         
00011         Permission is hereby granted to anyone to use this software for any 
00012         purpose, including commercial applications, and to alter it and/or 
00013         redistribute it freely, subject to the following restrictions:
00014         
00015         1. The origin of this software must not be misrepresented; you must 
00016            not claim that you wrote the original software. If you use this 
00017            software in a product, an acknowledgment within documentation of 
00018            said product would be appreciated but is not required.
00019 
00020         2. Altered source versions must be plainly marked as such, and must 
00021            not be misrepresented as being the original software.
00022 
00023         3. This notice may not be removed or altered from any distribution
00024            of the source.
00025 
00026 
00027                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
00028 
00029 
00030         @version        Initial version, March 2004      
00031         @author         Kris
00032 
00033 
00034 *******************************************************************************/
00035 
00036 module mango.io.Resource;
00037 
00038 private import  mango.io.model.IConduit,
00039                 mango.io.model.IResource;
00040 
00041 /*******************************************************************************
00042 
00043         Protocol for acquiring and releasing a resource such as a file, or
00044         socket. This isn't strictly necessary, but will aid migration to a
00045         multi-threaded runtime environment.
00046 
00047 *******************************************************************************/
00048 
00049 class Resource : IResource
00050 {
00051         protected Object  _lock;
00052         private   int     usage;
00053 
00054         /***********************************************************************
00055         
00056                 Subclasses must implement closure mechanics. This is 
00057                 invoked when the number of close() invocations match
00058                 that of aquire()  --  the latter is typically called 
00059                 immediately following the successful construction of
00060                 an IResource implementation; one should expect close
00061                 to be required at least once.
00062 
00063         ***********************************************************************/
00064 
00065         abstract protected void closure (); 
00066            
00067 
00068         /***********************************************************************
00069         
00070                 Set the default lock to be this object
00071 
00072         ***********************************************************************/
00073 
00074         this ()
00075         {
00076                 _lock = this;
00077         }
00078 
00079         /***********************************************************************
00080         
00081                 Make a reasonable attempt to clean up
00082 
00083         ***********************************************************************/
00084 
00085         ~this ()
00086         {
00087                 version (TraceLinux)
00088                         {
00089                         printf ("closing resource via destructor\n");
00090                         }
00091 
00092                 close();
00093         }
00094 
00095         /***********************************************************************
00096         
00097                 Return the lock used by this resource
00098 
00099         ***********************************************************************/
00100 
00101         Object getLock ()
00102         {
00103                 synchronized (_lock)
00104                               return _lock;
00105         }
00106 
00107         /***********************************************************************
00108         
00109                 Set an alternate lock. Typically one would use this to 
00110                 synchronize multiple different Resource via a common
00111                 object. 
00112 
00113         ***********************************************************************/
00114 
00115         void setLock (Object lock)
00116         in {
00117            assert (lock);
00118            }
00119         body
00120         {
00121                 synchronized (_lock)
00122                               _lock = lock;
00123         }
00124 
00125         /***********************************************************************
00126         
00127                 hold a reference to this resource. The caller is now
00128                 responsible for invoking close() upon this resource;
00129 
00130         ***********************************************************************/
00131 
00132         void acquire ()
00133         {
00134                 synchronized (_lock)
00135                              {
00136                              ++usage;
00137                              }
00138         }
00139 
00140         /***********************************************************************
00141                 
00142                 If this resource is still open, acquire it and return true.
00143                 This is a threadsafe test-and-set mechanism that fails only
00144                 if the resource is already closed, or was never opened.
00145 
00146                 Note that you are responsible for invoking close() whenever
00147                 this method returns true.
00148 
00149         ***********************************************************************/
00150 
00151         bool acquireIfOpen ()
00152         {
00153                 synchronized (_lock)
00154                              {
00155                              if (usage > 0)
00156                                 {
00157                                 ++usage;
00158                                 return true;
00159                                 }
00160                              return false;
00161                              }
00162         }               
00163 
00164         /***********************************************************************
00165         
00166                 release a reference to this resource
00167 
00168         ***********************************************************************/
00169 
00170         void close ()
00171         {
00172                 synchronized (_lock)
00173                              {
00174                              if (--usage == 0)
00175                                  closure();
00176                              }
00177         }
00178 }

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