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 // __thread keyword is supported if configure detected it or when using mingw32
  26 // >= 4.3 which is known to have it too
  27 #elif defined(HAVE___THREAD_KEYWORD) || \
  28         (defined(__MINGW32__) && wxCHECK_GCC_VERSION(4, 3))
  29     #define wxHAS_COMPILER_TLS
  30     #define wxTHREAD_SPECIFIC_DECL __thread
  31 // MSVC has its own version which might be supported by some other Windows
  32 // compilers, to be tested
  33 #elif wxCHECK_VISUALC_VERSION(7)
  34     #define wxHAS_COMPILER_TLS
  35     #define wxTHREAD_SPECIFIC_DECL __declspec(thread)
  36 #endif
  37
  38 // ----------------------------------------------------------------------------
  39 // define wxTLS_TYPE()
  40 // ----------------------------------------------------------------------------
  41
  42 #ifdef wxHAS_COMPILER_TLS
  43     #define wxTLS_TYPE(T) wxTHREAD_SPECIFIC_DECL T
  44     #define wxTLS_PTR(var) (&(var))
  45     #define wxTLS_VALUE(var) (var)
  46 #else // !wxHAS_COMPILER_TLS
  47     #ifdef __WXMSW__
  48         #include "wx/msw/tls.h"
  49     #elif defined(__UNIX__)
  50         #include "wx/unix/tls.h"
  51     #else
  52         // TODO: we could emulate TLS for such platforms...
  53         #error Neither compiler nor OS support thread-specific variables.
  54     #endif
  55
  56     #include <stdlib.h> // for calloc()
  57
  58     // wxTlsValue<T> represents a thread-specific value of type T but, unlike
  59     // with native compiler thread-specific variables, it behaves like a
  60     // (never NULL) pointer to T and so needs to be dereferenced before use
  61     template <typename T>
  62     class wxTlsValue
  63     {
  64     public:
  65         typedef T ValueType;
  66
  67         // ctor doesn't do anything, the object is created on first access
  68         //
  69         // FIXME: the thread-specific values are currently not freed under
  70         //        Windows, resulting in memory leaks, this must be implemented
  71         //        there somehow (probably by keeping a list of all TLS objects
  72         //        and cleaning them up in wxThread cleanup)
  73         wxTlsValue()
  74 #ifdef __UNIX__
  75             : m_key(free)
  76 #endif
  77         {
  78         }
  79
  80         // dtor is only called in the main thread context and so is not enough
  81         // to free memory allocated by us for the other threads, we use
  82         // destructor function when using Pthreads for this (which is not
  83         // called for the main thread as it doesn't call pthread_exit() but
  84         // just to be safe we also reset the key anyhow) and simply leak the
  85         // memory under Windows (see the FIXME above)
  86         ~wxTlsValue()
  87         {
  88             void * const value = m_key.Get();
  89             if ( value)
  90             {
  91                 free(value);
  92                 m_key.Set(NULL);
  93             }
  94         }
  95
  96         // access the object creating it on demand
  97         ValueType *Get()
  98         {
  99             void *value = m_key.Get();
 100             if ( !value )
 101             {
 102                 // ValueType must be POD to be used in wxHAS_COMPILER_TLS case
 103                 // anyhow (at least gcc doesn't accept non-POD values being
 104                 // declared with __thread) so initialize it as a POD too
 105                 value = calloc(1, sizeof(ValueType));
 106
 107                 if ( !m_key.Set(value) )
 108                 {
 109                     free(value);
 110
 111                     // this will probably result in a crash in the caller but
 112                     // it's arguably better to crash immediately instead of
 113                     // slowly dying from out-of-memory errors which would
 114                     // happen as the next access to this object would allocate
 115                     // another ValueType instance and so on forever
 116                     value = NULL;
 117                 }
 118             }
 119
 120             return static_cast<ValueType *>(value);
 121         }
 122
 123         // pointer-like accessors
 124         ValueType *operator->() { return Get(); }
 125         ValueType& operator*() { return *Get(); }
 126
 127     private:
 128         wxTlsKey m_key;
 129
 130         DECLARE_NO_COPY_TEMPLATE_CLASS(wxTlsValue, T)
 131     };
 132
 133     #define wxTLS_TYPE(T) wxTlsValue<T>
 134     #define wxTLS_PTR(var) (var)
 135     #define wxTLS_VALUE(var) (*(var))
 136 #endif // wxHAS_COMPILER_TLS/!wxHAS_COMPILER_TLS
 137
 138 #endif // _WX_TLS_H_
 139