include/wx/tls.h

   1 ///////////////////////////////////////////////////////////////////////////////
   2 // Name:        wx/tls.h
   3 // Purpose:     Implementation of thread local storage
   4 // Author:      Vadim Zeitlin
   5 // Created:     2008-08-08
   6 // RCS-ID:      $Id$
   7 // Copyright:   (c) 2008 Vadim Zeitlin <vadim@wxwidgets.org>
   8 // Licence:     wxWindows licence
   9 ///////////////////////////////////////////////////////////////////////////////
  10
  11 #ifndef _WX_TLS_H_
  12 #define _WX_TLS_H_
  13
  14 #include "wx/defs.h"
  15
  16 // ----------------------------------------------------------------------------
  17 // check for compiler support of thread-specific variables
  18 // ----------------------------------------------------------------------------
  19
  20 // when not using threads at all, there is no need for thread-specific
  21 // values to be really thread-specific
  22 #if !wxUSE_THREADS
  23     #define wxHAS_COMPILER_TLS
  24     #define wxTHREAD_SPECIFIC_DECL
  25 // otherwise try to find the compiler-specific way to handle TLS unless
  26 // explicitly disabled by setting wxUSE_COMPILER_TLS to 0 (it is 1 by default).
  27 #elif wxUSE_COMPILER_TLS
  28 // __thread keyword is not supported correctly by MinGW, at least in some
  29 // configurations, see http://sourceforge.net/support/tracker.php?aid=2837047
  30 // and when in doubt we prefer to not use it at all.
  31 #if defined(HAVE___THREAD_KEYWORD) && !defined(__MINGW32__)
  32     #define wxHAS_COMPILER_TLS
  33     #define wxTHREAD_SPECIFIC_DECL __thread
  34 // MSVC has its own version which might be supported by some other Windows
  35 // compilers, to be tested
  36 #elif wxCHECK_VISUALC_VERSION(7)
  37     #define wxHAS_COMPILER_TLS
  38     #define wxTHREAD_SPECIFIC_DECL __declspec(thread)
  39 #endif // compilers
  40 #endif // wxUSE_COMPILER_TLS
  41
  42 // ----------------------------------------------------------------------------
  43 // define wxTLS_TYPE()
  44 // ----------------------------------------------------------------------------
  45
  46 #ifdef wxHAS_COMPILER_TLS
  47     #define wxTLS_TYPE(T) wxTHREAD_SPECIFIC_DECL T
  48     #define wxTLS_PTR(var) (&(var))
  49     #define wxTLS_VALUE(var) (var)
  50 #else // !wxHAS_COMPILER_TLS
  51
  52     extern "C"
  53     {
  54         typedef void (*wxTlsDestructorFunction)(void*);
  55     }
  56
  57     #if defined(__WINDOWS__)
  58         #include "wx/msw/tls.h"
  59     #elif defined(__OS2__)
  60         #include "wx/os2/tls.h"
  61     #elif defined(__UNIX__)
  62         #include "wx/unix/tls.h"
  63     #else
  64         // TODO: we could emulate TLS for such platforms...
  65         #error Neither compiler nor OS support thread-specific variables.
  66     #endif
  67
  68     #include <stdlib.h> // for calloc()
  69
  70     // wxTlsValue<T> represents a thread-specific value of type T but, unlike
  71     // with native compiler thread-specific variables, it behaves like a
  72     // (never NULL) pointer to T and so needs to be dereferenced before use
  73     //
  74     // Note: T must be a POD!
  75     //
  76     // Note: On Unix, thread-specific T value is freed when the thread exits.
  77     //       On Windows, thread-specific values are freed later, when given
  78     //       wxTlsValue<T> is destroyed.  The only exception to this is the
  79     //       value for the main thread, which is always freed when
  80     //       wxTlsValue<T> is destroyed.
  81     template <typename T>
  82     class wxTlsValue
  83     {
  84     public:
  85         typedef T ValueType;
  86
  87         // ctor doesn't do anything, the object is created on first access
  88         wxTlsValue() : m_key(free) {}
  89
  90         // dtor is only called in the main thread context and so is not enough
  91         // to free memory allocated by us for the other threads, we use
  92         // destructor function when using Pthreads for this (which is not
  93         // called for the main thread as it doesn't call pthread_exit() but
  94         // just to be safe we also reset the key anyhow)
  95         ~wxTlsValue()
  96         {
  97             if ( m_key.Get() )
  98                 m_key.Set(NULL); // this deletes the value
  99         }
 100
 101         // access the object creating it on demand
 102         ValueType *Get()
 103         {
 104             void *value = m_key.Get();
 105             if ( !value )
 106             {
 107                 // ValueType must be POD to be used in wxHAS_COMPILER_TLS case
 108                 // anyhow (at least gcc doesn't accept non-POD values being
 109                 // declared with __thread) so initialize it as a POD too
 110                 value = calloc(1, sizeof(ValueType));
 111
 112                 if ( !m_key.Set(value) )
 113                 {
 114                     free(value);
 115
 116                     // this will probably result in a crash in the caller but
 117                     // it's arguably better to crash immediately instead of
 118                     // slowly dying from out-of-memory errors which would
 119                     // happen as the next access to this object would allocate
 120                     // another ValueType instance and so on forever
 121                     value = NULL;
 122                 }
 123             }
 124
 125             return static_cast<ValueType *>(value);
 126         }
 127
 128         // pointer-like accessors
 129         ValueType *operator->() { return Get(); }
 130         ValueType& operator*() { return *Get(); }
 131
 132     private:
 133         wxTlsKey m_key;
 134
 135         DECLARE_NO_COPY_TEMPLATE_CLASS(wxTlsValue, T)
 136     };
 137
 138     #define wxTLS_TYPE(T) wxTlsValue<T>
 139     #define wxTLS_PTR(var) ((var).Get())
 140     #define wxTLS_VALUE(var) (*(var))
 141 #endif // wxHAS_COMPILER_TLS/!wxHAS_COMPILER_TLS
 142
 143 #endif // _WX_TLS_H_
 144