Make glfwGetError also provide description

Related to #970.

README.md

@@ -122,7 +122,8 @@ information on what to include when reporting a bug.
 
 ## Changelog
 
-- Added `glfwGetError` function for querying the last error code (#970)
+- Added `glfwGetError` function for querying the last error code and its
+  description (#970)
 - Added `glfwRequestWindowAttention` function for requesting attention from the
   user (#732,#988)
 - Added `glfwGetKeyScancode` function that allows retrieving platform dependent

docs/intro.dox

@@ -128,15 +128,19 @@ immediately.
 @section error_handling Error handling
 
 Some GLFW functions have return values that indicate an error, but this is often
-not very helpful when trying to figure out _why_ the error occurred.  Other
-functions have no return value reserved for errors, so error notification needs
-a separate channel.  Finally, far from all GLFW functions have return values.
+not very helpful when trying to figure out what happened or why it occurred.
+Other functions have no return value reserved for errors, so error notification
+needs a separate channel.  Finally, far from all GLFW functions have return
+values.
 
-The last error code for the calling thread can be queried at any time with @ref
-glfwGetError.
+The last [error code](@ref errors) for the calling thread can be queried at any
+time with @ref glfwGetError.
 
 @code
-int error = glfwGetError();
+int code = glfwGetError(NULL);
+
+if (code != GLFW_NO_ERROR)
+    handle_error(code);
 @endcode
 
 If no error has occurred since the last call, @ref GLFW_NO_ERROR is returned.
@@ -146,42 +150,52 @@ The error code indicates the general category of the error.  Some error codes,
 such as @ref GLFW_NOT_INITIALIZED has only a single meaning, whereas others like
 @ref GLFW_PLATFORM_ERROR are used for many different errors.
 
-GLFW usually has much more information about the error than its general category
-at the point where it occurred.  This is where the error callback comes in.
-This callback is called whenever an error occurs.  It is set with @ref
-glfwSetErrorCallback, a function that may be called regardless of whether GLFW
-is initialized.
+GLFW often has more information about an error than its general category.  You
+can retrieve a UTF-8 encoded human-readable description along with the error
+code.  If no error has occurred since the last call, the description is set to
+`NULL`.
+
+@code
+const char* description;
+int code = glfwGetError(&description);
+
+if (description)
+    display_error_message(code, description);
+@endcode
+
+The retrieved description string is only valid until the next error occurs.
+This means you must make a copy of it if you want to keep it.
+
+You can also set an error callback, which will be called each time an error
+occurs.  It is set with @ref glfwSetErrorCallback.
 
 @code
 glfwSetErrorCallback(error_callback);
 @endcode
 
-The error callback receives a human-readable description of the error and (when
-possible) its cause.  The description encoded as UTF-8.  The callback is also
-provided with an [error code](@ref errors). 
+The error callback receives the same error code and human-readable description
+returned by @ref glfwGetError.
 
 @code
-void error_callback(int error, const char* description)
+void error_callback(int code, const char* description)
 {
-    puts(description);
+    display_error_message(code, description);
 }
 @endcode
 
-The error callback is called after the error code is set, so calling @ref
-glfwGetError from within the error callback returns the same value as the
+The error callback is called after the error is stored, so calling @ref
+glfwGetError from within the error callback returns the same values as the
 callback argument.
 
+The description string passed to the callback is only valid until the error
+callback returns.  This means you must make a copy of it if you want to keep it.
+
 __Reported errors are never fatal.__  As long as GLFW was successfully
 initialized, it will remain initialized and in a safe state until terminated
 regardless of how many errors occur.  If an error occurs during initialization
 that causes @ref glfwInit to fail, any part of the library that was initialized
 will be safely terminated.
 
-The description string is only valid until the error callback returns, as it may
-have been generated specifically for that error.  This lets GLFW provide much
-more specific error descriptions but means you must make a copy if you want to
-keep the description string.
-
 Do not rely on a currently invalid call to generate a specific error, as in the
 future that same call may generate a different error or become valid.
 

docs/news.dox

@@ -7,8 +7,8 @@
 
 @subsection news_33_geterror Error query
 
-GLFW now supports querying the last error code for the calling thread with @ref
-glfwGetError.
+GLFW now supports querying the last error code for the calling thread and its
+human-readable description with @ref glfwGetError.
 
 @see @ref error_handling
 

include/GLFW/glfw3.h

@@ -1646,13 +1646,20 @@ GLFWAPI const char* glfwGetVersionString(void);
 /*! @brief Returns and clears the last error for the calling thread.
  *
  *  This function returns and clears the [error code](@ref error) of the last
- *  error that occurred on the calling thread.  If no error has occurred since
- *  the last call, it returns @ref GLFW_NO_ERROR.
+ *  error that occurred on the calling thread, and optionally a UTF-8 encoded
+ *  human-readable description of it.  If no error has occurred since the last
+ *  call, it returns @ref GLFW_NO_ERROR and the description pointer is set to
+ *  `NULL`.
  *
+ *  @param[in] description Where to store the error description pointer, or `NULL`.
  *  @return The last error code for the calling thread, or @ref GLFW_NO_ERROR.
  *
  *  @errors None.
  *
+ *  @pointer_lifetime The returned string is allocated and freed by GLFW.  You
+ *  should not free it yourself.  It is guaranteed to be valid only until the
+ *  next error occurs or the library is terminated.
+ *
  *  @remark This function may be called before @ref glfwInit.
  *
  *  @thread_safety This function may be called from any thread.
@@ -1664,7 +1671,7 @@ GLFWAPI const char* glfwGetVersionString(void);
  *
  *  @ingroup init
  */
-GLFWAPI int glfwGetError(void);
+GLFWAPI int glfwGetError(const char** description);
 
 /*! @brief Sets the error callback.
  *

src/context.c

@@ -331,7 +331,7 @@ GLFWbool _glfwRefreshContextAttribs(const _GLFWctxconfig* ctxconfig)
         NULL
     };
 
-    window = _glfwPlatformGetTls(&_glfw.context);
+    window = _glfwPlatformGetTls(&_glfw.contextSlot);
 
     window->context.source = ctxconfig->source;
     window->context.client = GLFW_OPENGL_API;
@@ -578,7 +578,7 @@ GLFWbool _glfwStringInExtensionString(const char* string, const char* extensions
 GLFWAPI void glfwMakeContextCurrent(GLFWwindow* handle)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFWwindow* previous = _glfwPlatformGetTls(&_glfw.context);
+    _GLFWwindow* previous = _glfwPlatformGetTls(&_glfw.contextSlot);
 
     _GLFW_REQUIRE_INIT();
 
@@ -601,7 +601,7 @@ GLFWAPI void glfwMakeContextCurrent(GLFWwindow* handle)
 GLFWAPI GLFWwindow* glfwGetCurrentContext(void)
 {
     _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
-    return _glfwPlatformGetTls(&_glfw.context);
+    return _glfwPlatformGetTls(&_glfw.contextSlot);
 }
 
 GLFWAPI void glfwSwapBuffers(GLFWwindow* handle)
@@ -626,7 +626,7 @@ GLFWAPI void glfwSwapInterval(int interval)
 
     _GLFW_REQUIRE_INIT();
 
-    window = _glfwPlatformGetTls(&_glfw.context);
+    window = _glfwPlatformGetTls(&_glfw.contextSlot);
     if (!window)
     {
         _glfwInputError(GLFW_NO_CURRENT_CONTEXT, NULL);
@@ -643,7 +643,7 @@ GLFWAPI int glfwExtensionSupported(const char* extension)
 
     _GLFW_REQUIRE_INIT_OR_RETURN(GLFW_FALSE);
 
-    window = _glfwPlatformGetTls(&_glfw.context);
+    window = _glfwPlatformGetTls(&_glfw.contextSlot);
     if (!window)
     {
         _glfwInputError(GLFW_NO_CURRENT_CONTEXT, NULL);
@@ -708,7 +708,7 @@ GLFWAPI GLFWglproc glfwGetProcAddress(const char* procname)
 
     _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
 
-    window = _glfwPlatformGetTls(&_glfw.context);
+    window = _glfwPlatformGetTls(&_glfw.contextSlot);
     if (!window)
     {
         _glfwInputError(GLFW_NO_CURRENT_CONTEXT, NULL);

src/egl_context.c

@@ -199,12 +199,12 @@ static void makeContextCurrentEGL(_GLFWwindow* window)
         }
     }
 
-    _glfwPlatformSetTls(&_glfw.context, window);
+    _glfwPlatformSetTls(&_glfw.contextSlot, window);
 }
 
 static void swapBuffersEGL(_GLFWwindow* window)
 {
-    if (window != _glfwPlatformGetTls(&_glfw.context))
+    if (window != _glfwPlatformGetTls(&_glfw.contextSlot))
     {
         _glfwInputError(GLFW_PLATFORM_ERROR,
                         "EGL: The context must be current on the calling thread when swapping buffers");
@@ -233,7 +233,7 @@ static int extensionSupportedEGL(const char* extension)
 
 static GLFWglproc getProcAddressEGL(const char* procname)
 {
-    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.context);
+    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.contextSlot);
 
     if (window->context.egl.client)
     {

src/glx_context.c

@@ -165,7 +165,7 @@ static void makeContextCurrentGLX(_GLFWwindow* window)
         }
     }
 
-    _glfwPlatformSetTls(&_glfw.context, window);
+    _glfwPlatformSetTls(&_glfw.contextSlot, window);
 }
 
 static void swapBuffersGLX(_GLFWwindow* window)
@@ -175,7 +175,7 @@ static void swapBuffersGLX(_GLFWwindow* window)
 
 static void swapIntervalGLX(int interval)
 {
-    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.context);
+    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.contextSlot);
 
     if (_glfw.glx.EXT_swap_control)
     {

src/init.c

@@ -43,7 +43,7 @@ _GLFWlibrary _glfw = { GLFW_FALSE };
 // These are outside of _glfw so they can be used before initialization and
 // after termination
 //
-static int _glfwErrorCode;
+static _GLFWerror _glfwMainThreadError;
 static GLFWerrorfun _glfwErrorCallback;
 static _GLFWinitconfig _glfwInitHints =
 {
@@ -56,9 +56,9 @@ static _GLFWinitconfig _glfwInitHints =
 
 // Returns a generic string representation of the specified error
 //
-static const char* getErrorString(int error)
+static const char* getErrorString(int code)
 {
-    switch (error)
+    switch (code)
     {
         case GLFW_NOT_INITIALIZED:
             return "The GLFW library is not initialized";
@@ -114,11 +114,18 @@ static void terminate(void)
     _glfwTerminateVulkan();
     _glfwPlatformTerminate();
 
-    if (_glfwPlatformIsValidTls(&_glfw.error))
-        _glfwErrorCode = (int) (intptr_t) _glfwPlatformGetTls(&_glfw.error);
+    _glfw.initialized = GLFW_FALSE;
 
-    _glfwPlatformDestroyTls(&_glfw.context);
-    _glfwPlatformDestroyTls(&_glfw.error);
+    while (_glfw.errorListHead)
+    {
+        _GLFWerror* error = _glfw.errorListHead;
+        _glfw.errorListHead = error->next;
+        free(error);
+    }
+
+    _glfwPlatformDestroyTls(&_glfw.contextSlot);
+    _glfwPlatformDestroyTls(&_glfw.errorSlot);
+    _glfwPlatformDestroyMutex(&_glfw.errorLock);
 
     memset(&_glfw, 0, sizeof(_glfw));
 }
@@ -128,17 +135,10 @@ static void terminate(void)
 //////                         GLFW event API                       //////
 //////////////////////////////////////////////////////////////////////////
 
-void _glfwInputError(int error, const char* format, ...)
+void _glfwInputError(int code, const char* format, ...)
 {
-    if (_glfw.initialized)
-        _glfwPlatformSetTls(&_glfw.error, (void*) (intptr_t) error);
-    else
-        _glfwErrorCode = error;
-
-    if (_glfwErrorCallback)
-    {
-        char buffer[8192];
-        const char* description;
+    _GLFWerror* error;
+    char description[1024];
 
     if (format)
     {
@@ -146,19 +146,36 @@ void _glfwInputError(int error, const char* format, ...)
         va_list vl;
 
         va_start(vl, format);
-            count = vsnprintf(buffer, sizeof(buffer), format, vl);
+        count = vsnprintf(description, sizeof(description), format, vl);
         va_end(vl);
 
         if (count < 0)
-                buffer[sizeof(buffer) - 1] = '\0';
-
-            description = buffer;
+            description[sizeof(description) - 1] = '\0';
     }
     else
-            description = getErrorString(error);
+        strcpy(description, getErrorString(code));
 
-        _glfwErrorCallback(error, description);
+    if (_glfw.initialized)
+    {
+        error = _glfwPlatformGetTls(&_glfw.errorSlot);
+        if (!error)
+        {
+            error = calloc(1, sizeof(_GLFWerror));
+            _glfwPlatformSetTls(&_glfw.errorSlot, error);
+            _glfwPlatformLockMutex(&_glfw.errorLock);
+            error->next = _glfw.errorListHead;
+            _glfw.errorListHead = error;
+            _glfwPlatformUnlockMutex(&_glfw.errorLock);
+        }
     }
+    else
+        error = &_glfwMainThreadError;
+
+    error->code = code;
+    strcpy(error->description, description);
+
+    if (_glfwErrorCallback)
+        _glfwErrorCallback(code, description);
 }
 
 
@@ -180,12 +197,14 @@ GLFWAPI int glfwInit(void)
         return GLFW_FALSE;
     }
 
-    if (!_glfwPlatformCreateTls(&_glfw.error))
+    if (!_glfwPlatformCreateMutex(&_glfw.errorLock))
         return GLFW_FALSE;
-    if (!_glfwPlatformCreateTls(&_glfw.context))
+    if (!_glfwPlatformCreateTls(&_glfw.errorSlot))
+        return GLFW_FALSE;
+    if (!_glfwPlatformCreateTls(&_glfw.contextSlot))
         return GLFW_FALSE;
 
-    _glfwPlatformSetTls(&_glfw.error, (void*) (intptr_t) _glfwErrorCode);
+    _glfwPlatformSetTls(&_glfw.errorSlot, &_glfwMainThreadError);
 
     _glfw.initialized = GLFW_TRUE;
     _glfw.timer.offset = _glfwPlatformGetTimerValue();
@@ -237,22 +256,28 @@ GLFWAPI const char* glfwGetVersionString(void)
     return _glfwPlatformGetVersionString();
 }
 
-GLFWAPI int glfwGetError(void)
+GLFWAPI int glfwGetError(const char** description)
 {
-    int error;
+    _GLFWerror* error;
+    int code = GLFW_NO_ERROR;
+
+    if (description)
+        *description = NULL;
 
     if (_glfw.initialized)
-    {
-        error = (int) (intptr_t) _glfwPlatformGetTls(&_glfw.error);
-        _glfwPlatformSetTls(&_glfw.error, (void*) (intptr_t) GLFW_NO_ERROR);
-    }
+        error = _glfwPlatformGetTls(&_glfw.errorSlot);
     else
+        error = &_glfwMainThreadError;
+
+    if (error)
     {
-        error = _glfwErrorCode;
-        _glfwErrorCode = GLFW_NO_ERROR;
+        code = error->code;
+        error->code = GLFW_NO_ERROR;
+        if (description && code)
+            *description = error->description;
     }
 
-    return error;
+    return code;
 }
 
 GLFWAPI GLFWerrorfun glfwSetErrorCallback(GLFWerrorfun cbfun)

src/internal.h

@@ -55,6 +55,7 @@
 
 typedef int GLFWbool;
 
+typedef struct _GLFWerror       _GLFWerror;
 typedef struct _GLFWinitconfig  _GLFWinitconfig;
 typedef struct _GLFWwndconfig   _GLFWwndconfig;
 typedef struct _GLFWctxconfig   _GLFWctxconfig;
@@ -66,6 +67,7 @@ typedef struct _GLFWmonitor     _GLFWmonitor;
 typedef struct _GLFWcursor      _GLFWcursor;
 typedef struct _GLFWjoystick    _GLFWjoystick;
 typedef struct _GLFWtls         _GLFWtls;
+typedef struct _GLFWmutex       _GLFWmutex;
 
 typedef void (* _GLFWmakecontextcurrentfun)(_GLFWwindow*);
 typedef void (* _GLFWswapbuffersfun)(_GLFWwindow*);
@@ -257,6 +259,13 @@ typedef void (APIENTRY * PFN_vkVoidFunction)(void);
 // Platform-independent structures
 //========================================================================
 
+struct _GLFWerror
+{
+    _GLFWerror*     next;
+    int             code;
+    char            description[1024];
+};
+
 /*! @brief Initialization configuration.
  *
  *  Parameters relating to the initialization of the library.
@@ -490,6 +499,14 @@ struct _GLFWtls
     _GLFW_PLATFORM_TLS_STATE;
 };
 
+/*! @brief Mutex structure.
+ */
+struct _GLFWmutex
+{
+    // This is defined in the platform's tls.h
+    _GLFW_PLATFORM_MUTEX_STATE;
+};
+
 /*! @brief Library global data.
  */
 struct _GLFWlibrary
@@ -504,8 +521,8 @@ struct _GLFWlibrary
         int             refreshRate;
     } hints;
 
+    _GLFWerror*         errorListHead;
     _GLFWcursor*        cursorListHead;
-
     _GLFWwindow*        windowListHead;
 
     _GLFWmonitor**      monitors;
@@ -513,8 +530,9 @@ struct _GLFWlibrary
 
     _GLFWjoystick       joysticks[GLFW_JOYSTICK_LAST + 1];
 
-    _GLFWtls            error;
-    _GLFWtls            context;
+    _GLFWtls            errorSlot;
+    _GLFWtls            contextSlot;
+    _GLFWmutex          errorLock;
 
     struct {
         uint64_t        offset;
@@ -651,7 +669,11 @@ GLFWbool _glfwPlatformCreateTls(_GLFWtls* tls);
 void _glfwPlatformDestroyTls(_GLFWtls* tls);
 void* _glfwPlatformGetTls(_GLFWtls* tls);
 void _glfwPlatformSetTls(_GLFWtls* tls, void* value);
-GLFWbool _glfwPlatformIsValidTls(_GLFWtls* tls);
+
+GLFWbool _glfwPlatformCreateMutex(_GLFWmutex* mutex);
+void _glfwPlatformDestroyMutex(_GLFWmutex* mutex);
+void _glfwPlatformLockMutex(_GLFWmutex* mutex);
+void _glfwPlatformUnlockMutex(_GLFWmutex* mutex);
 
 /*! @} */
 
@@ -798,15 +820,15 @@ void _glfwInputMonitor(_GLFWmonitor* monitor, int action, int placement);
 void _glfwInputMonitorWindow(_GLFWmonitor* monitor, _GLFWwindow* window);
 
 /*! @brief Notifies shared code of an error.
- *  @param[in] error The error code most suitable for the error.
+ *  @param[in] code The error code most suitable for the error.
  *  @param[in] format The `printf` style format string of the error
  *  description.
  *  @ingroup event
  */
 #if defined(__GNUC__)
-void _glfwInputError(int error, const char* format, ...) __attribute__((format(printf, 2, 3)));
+void _glfwInputError(int code, const char* format, ...) __attribute__((format(printf, 2, 3)));
 #else
-void _glfwInputError(int error, const char* format, ...);
+void _glfwInputError(int code, const char* format, ...);
 #endif
 
 /*! @brief Notifies shared code of files or directories dropped on a window.

src/nsgl_context.m

@@ -34,7 +34,7 @@ static void makeContextCurrentNSGL(_GLFWwindow* window)
     else
         [NSOpenGLContext clearCurrentContext];
 
-    _glfwPlatformSetTls(&_glfw.context, window);
+    _glfwPlatformSetTls(&_glfw.contextSlot, window);
 }
 
 static void swapBuffersNSGL(_GLFWwindow* window)
@@ -45,7 +45,7 @@ static void swapBuffersNSGL(_GLFWwindow* window)
 
 static void swapIntervalNSGL(int interval)
 {
-    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.context);
+    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.contextSlot);
 
     GLint sync = interval;
     [window->context.nsgl.object setValues:&sync

src/osmesa_context.c

@@ -63,7 +63,7 @@ static void makeContextCurrentOSMesa(_GLFWwindow* window)
         }
     }
 
-    _glfwPlatformSetTls(&_glfw.context, window);
+    _glfwPlatformSetTls(&_glfw.contextSlot, window);
 }
 
 static GLFWglproc getProcAddressOSMesa(const char* procname)

src/posix_tls.c

@@ -69,8 +69,35 @@ void _glfwPlatformSetTls(_GLFWtls* tls, void* value)
     pthread_setspecific(tls->posix.key, value);
 }
 
-GLFWbool _glfwPlatformIsValidTls(_GLFWtls* tls)
+GLFWbool _glfwPlatformCreateMutex(_GLFWmutex* mutex)
 {
-    return tls->posix.allocated;
+    assert(mutex->posix.allocated == GLFW_FALSE);
+
+    if (pthread_mutex_init(&mutex->posix.handle, NULL) != 0)
+    {
+        _glfwInputError(GLFW_PLATFORM_ERROR, "POSIX: Failed to create mutex");
+        return GLFW_FALSE;
+    }
+
+    return mutex->posix.allocated = GLFW_TRUE;
+}
+
+void _glfwPlatformDestroyMutex(_GLFWmutex* mutex)
+{
+    if (mutex->posix.allocated)
+        pthread_mutex_destroy(&mutex->posix.handle);
+    memset(mutex, 0, sizeof(_GLFWmutex));
+}
+
+void _glfwPlatformLockMutex(_GLFWmutex* mutex)
+{
+    assert(mutex->posix.allocated == GLFW_TRUE);
+    pthread_mutex_lock(&mutex->posix.handle);
+}
+
+void _glfwPlatformUnlockMutex(_GLFWmutex* mutex)
+{
+    assert(mutex->posix.allocated == GLFW_TRUE);
+    pthread_mutex_unlock(&mutex->posix.handle);
 }
 

src/posix_tls.h

@@ -28,6 +28,7 @@
 #include <pthread.h>
 
 #define _GLFW_PLATFORM_TLS_STATE    _GLFWtlsPOSIX   posix
+#define _GLFW_PLATFORM_MUTEX_STATE  _GLFWmutexPOSIX posix
 
 
 // POSIX-specific thread local storage data
@@ -39,3 +40,12 @@ typedef struct _GLFWtlsPOSIX
 
 } _GLFWtlsPOSIX;
 
+// POSIX-specific mutex data
+//
+typedef struct _GLFWmutexPOSIX
+{
+    GLFWbool        allocated;
+    pthread_mutex_t handle;
+
+} _GLFWmutexPOSIX;
+

src/wgl_context.c

@@ -249,12 +249,12 @@ static void makeContextCurrentWGL(_GLFWwindow* window)
     if (window)
     {
         if (wglMakeCurrent(window->context.wgl.dc, window->context.wgl.handle))
-            _glfwPlatformSetTls(&_glfw.context, window);
+            _glfwPlatformSetTls(&_glfw.contextSlot, window);
         else
         {
             _glfwInputErrorWin32(GLFW_PLATFORM_ERROR,
                                  "WGL: Failed to make context current");
-            _glfwPlatformSetTls(&_glfw.context, NULL);
+            _glfwPlatformSetTls(&_glfw.contextSlot, NULL);
         }
     }
     else
@@ -265,7 +265,7 @@ static void makeContextCurrentWGL(_GLFWwindow* window)
                                  "WGL: Failed to clear current context");
         }
 
-        _glfwPlatformSetTls(&_glfw.context, NULL);
+        _glfwPlatformSetTls(&_glfw.contextSlot, NULL);
     }
 }
 
@@ -284,7 +284,7 @@ static void swapBuffersWGL(_GLFWwindow* window)
 
 static void swapIntervalWGL(int interval)
 {
-    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.context);
+    _GLFWwindow* window = _glfwPlatformGetTls(&_glfw.contextSlot);
 
     window->context.wgl.interval = interval;
 

src/win32_platform.h

@@ -221,6 +221,7 @@ typedef VkBool32 (APIENTRY *PFN_vkGetPhysicalDeviceWin32PresentationSupportKHR)(
 #define _GLFW_PLATFORM_MONITOR_STATE        _GLFWmonitorWin32 win32
 #define _GLFW_PLATFORM_CURSOR_STATE         _GLFWcursorWin32  win32
 #define _GLFW_PLATFORM_TLS_STATE            _GLFWtlsWin32     win32
+#define _GLFW_PLATFORM_MUTEX_STATE          _GLFWmutexWin32   win32
 
 
 // Win32-specific per-window data
@@ -334,6 +335,15 @@ typedef struct _GLFWtlsWin32
 
 } _GLFWtlsWin32;
 
+// Win32-specific mutex data
+//
+typedef struct _GLFWmutexWin32
+{
+    GLFWbool            allocated;
+    CRITICAL_SECTION    section;
+
+} _GLFWmutexWin32;
+
 
 GLFWbool _glfwRegisterWindowClassWin32(void);
 void _glfwUnregisterWindowClassWin32(void);

src/win32_tls.c

@@ -69,8 +69,29 @@ void _glfwPlatformSetTls(_GLFWtls* tls, void* value)
     TlsSetValue(tls->win32.index, value);
 }
 
-GLFWbool _glfwPlatformIsValidTls(_GLFWtls* tls)
+GLFWbool _glfwPlatformCreateMutex(_GLFWmutex* mutex)
 {
-    return tls->win32.allocated;
+    assert(mutex->win32.allocated == GLFW_FALSE);
+    InitializeCriticalSection(&mutex->win32.section);
+    return mutex->win32.allocated = GLFW_TRUE;
+}
+
+void _glfwPlatformDestroyMutex(_GLFWmutex* mutex)
+{
+    if (mutex->win32.allocated)
+        DeleteCriticalSection(&mutex->win32.section);
+    memset(mutex, 0, sizeof(_GLFWmutex));
+}
+
+void _glfwPlatformLockMutex(_GLFWmutex* mutex)
+{
+    assert(mutex->win32.allocated == GLFW_TRUE);
+    EnterCriticalSection(&mutex->win32.section);
+}
+
+void _glfwPlatformUnlockMutex(_GLFWmutex* mutex)
+{
+    assert(mutex->win32.allocated == GLFW_TRUE);
+    LeaveCriticalSection(&mutex->win32.section);
 }
 

src/window.c

@@ -192,7 +192,7 @@ GLFWAPI GLFWwindow* glfwCreateWindow(int width, int height,
     window->denom       = GLFW_DONT_CARE;
 
     // Save the currently current context so it can be restored later
-    previous = _glfwPlatformGetTls(&_glfw.context);
+    previous = _glfwPlatformGetTls(&_glfw.contextSlot);
     if (ctxconfig.client != GLFW_NO_API)
         glfwMakeContextCurrent(NULL);
 
@@ -408,7 +408,7 @@ GLFWAPI void glfwDestroyWindow(GLFWwindow* handle)
 
     // The window's context must not be current on another thread when the
     // window is destroyed
-    if (window == _glfwPlatformGetTls(&_glfw.context))
+    if (window == _glfwPlatformGetTls(&_glfw.contextSlot))
         glfwMakeContextCurrent(NULL);
 
     _glfwPlatformDestroyWindow(window);