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 not supported correctly by MinGW, at least in some
  26 // configurations, see http://sourceforge.net/support/tracker.php?aid=2837047
  27 // and when in doubt we prefer to not use it at all.
  28 #elif defined(HAVE___THREAD_KEYWORD) && !defined(__MINGW32__)
  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
  48     extern "C"
  49     {
  50         typedef void (*wxTlsDestructorFunction)(void*);
  51     }
  52
  53     #if defined(__WXMSW__)
  54         #include "wx/msw/tls.h"
  55     #elif defined(__OS2__)
  56         #include "wx/os2/tls.h"
  57     #elif defined(__UNIX__)
  58         #include "wx/unix/tls.h"
  59     #else
  60         // TODO: we could emulate TLS for such platforms...
  61         #error Neither compiler nor OS support thread-specific variables.
  62     #endif
  63
  64     #include <stdlib.h> // for calloc()
  65
  66     // wxTlsValue<T> represents a thread-specific value of type T but, unlike
  67     // with native compiler thread-specific variables, it behaves like a
  68     // (never NULL) pointer to T and so needs to be dereferenced before use
  69     //
  70     // Note: T must be a POD!
  71     //
  72     // Note: On Unix, thread-specific T value is freed when the thread exits.
  73     //       On Windows, thread-specific values are freed later, when given
  74     //       wxTlsValue<T> is destroyed.  The only exception to this is the
  75     //       value for the main thread, which is always freed when
  76     //       wxTlsValue<T> is destroyed.
  77     template <typename T>
  78     class wxTlsValue
  79     {
  80     public:
  81         typedef T ValueType;
  82
  83         // ctor doesn't do anything, the object is created on first access
  84         wxTlsValue() : m_key(free) {}
  85
  86         // dtor is only called in the main thread context and so is not enough
  87         // to free memory allocated by us for the other threads, we use
  88         // destructor function when using Pthreads for this (which is not
  89         // called for the main thread as it doesn't call pthread_exit() but
  90         // just to be safe we also reset the key anyhow)
  91         ~wxTlsValue()
  92         {
  93             if ( m_key.Get() )
  94                 m_key.Set(NULL); // this deletes the value
  95         }
  96
  97         // access the object creating it on demand
  98         ValueType *Get()
  99         {
 100             void *value = m_key.Get();
 101             if ( !value )
 102             {
 103                 // ValueType must be POD to be used in wxHAS_COMPILER_TLS case
 104                 // anyhow (at least gcc doesn't accept non-POD values being
 105                 // declared with __thread) so initialize it as a POD too
 106                 value = calloc(1, sizeof(ValueType));
 107
 108                 if ( !m_key.Set(value) )
 109                 {
 110                     free(value);
 111
 112                     // this will probably result in a crash in the caller but
 113                     // it's arguably better to crash immediately instead of
 114                     // slowly dying from out-of-memory errors which would
 115                     // happen as the next access to this object would allocate
 116                     // another ValueType instance and so on forever
 117                     value = NULL;
 118                 }
 119             }
 120
 121             return static_cast<ValueType *>(value);
 122         }
 123
 124         // pointer-like accessors
 125         ValueType *operator->() { return Get(); }
 126         ValueType& operator*() { return *Get(); }
 127
 128     private:
 129         wxTlsKey m_key;
 130
 131         DECLARE_NO_COPY_TEMPLATE_CLASS(wxTlsValue, T)
 132     };
 133
 134     #define wxTLS_TYPE(T) wxTlsValue<T>
 135     #define wxTLS_PTR(var) ((var).Get())
 136     #define wxTLS_VALUE(var) (*(var))
 137 #endif // wxHAS_COMPILER_TLS/!wxHAS_COMPILER_TLS
 138
 139 #endif // _WX_TLS_H_
 140