Improve logging performance and make log priorities thread-safe

Fixes https://github.com/libsdl-org/SDL/issues/9679

include/SDL3/SDL_log.h

@@ -120,7 +120,8 @@ typedef enum SDL_LogCategory
  */
 typedef enum SDL_LogPriority
 {
-    SDL_LOG_PRIORITY_VERBOSE = 1,
+    SDL_LOG_PRIORITY_INVALID,
+    SDL_LOG_PRIORITY_VERBOSE,
     SDL_LOG_PRIORITY_DEBUG,
     SDL_LOG_PRIORITY_INFO,
     SDL_LOG_PRIORITY_WARN,
@@ -135,6 +136,8 @@ typedef enum SDL_LogPriority
  *
  * \param priority the SDL_LogPriority to assign.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_ResetLogPriorities
@@ -148,14 +151,15 @@ extern SDL_DECLSPEC void SDLCALL SDL_SetLogPriorities(SDL_LogPriority priority);
  * \param category the category to assign a priority to.
  * \param priority the SDL_LogPriority to assign.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_GetLogPriority
  * \sa SDL_ResetLogPriorities
  * \sa SDL_SetLogPriorities
  */
-extern SDL_DECLSPEC void SDLCALL SDL_SetLogPriority(int category,
-                                                SDL_LogPriority priority);
+extern SDL_DECLSPEC void SDLCALL SDL_SetLogPriority(int category, SDL_LogPriority priority);
 
 /**
  * Get the priority of a particular log category.
@@ -163,6 +167,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_SetLogPriority(int category,
  * \param category the category to query.
  * \returns the SDL_LogPriority for the requested category.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_SetLogPriority
@@ -174,6 +180,8 @@ extern SDL_DECLSPEC SDL_LogPriority SDLCALL SDL_GetLogPriority(int category);
  *
  * This is called by SDL_Quit().
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_SetLogPriorities
@@ -194,6 +202,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_ResetLogPriorities(void);
  * \returns SDL_TRUE on success or SDL_FALSE on failure; call SDL_GetError()
  *          for more information.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_SetLogPriorities
@@ -208,6 +218,8 @@ extern SDL_DECLSPEC SDL_bool SDLCALL SDL_SetLogPriorityPrefix(SDL_LogPriority pr
  * \param ... additional parameters matching % tokens in the `fmt` string, if
  *            any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_LogCritical
@@ -229,6 +241,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_Log(SDL_PRINTF_FORMAT_STRING const char *fm
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -250,6 +264,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogVerbose(int category, SDL_PRINTF_FORMAT_
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -271,6 +287,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogDebug(int category, SDL_PRINTF_FORMAT_ST
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -292,6 +310,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogInfo(int category, SDL_PRINTF_FORMAT_STR
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -313,6 +333,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogWarn(int category, SDL_PRINTF_FORMAT_STR
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -334,6 +356,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogError(int category, SDL_PRINTF_FORMAT_ST
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -356,6 +380,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogCritical(int category, SDL_PRINTF_FORMAT
  * \param ... additional parameters matching % tokens in the **fmt** string,
  *            if any.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -379,6 +405,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogMessage(int category,
  * \param fmt a printf() style message format string.
  * \param ap a variable argument list.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_Log
@@ -397,7 +425,7 @@ extern SDL_DECLSPEC void SDLCALL SDL_LogMessageV(int category,
 /**
  * The prototype for the log output callback function.
  *
- * This function is called by SDL when there is new text to be logged.
+ * This function is called by SDL when there is new text to be logged. A mutex is held so that this function is never called by more than one thread at once.
  *
  * \param userdata what was passed as `userdata` to
  *                 SDL_SetLogOutputFunction().
@@ -417,6 +445,8 @@ typedef void (SDLCALL *SDL_LogOutputFunction)(void *userdata, int category, SDL_
  * \param userdata a pointer filled in with the pointer that is passed to
  *                 `callback`.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_SetLogOutputFunction
@@ -429,6 +459,8 @@ extern SDL_DECLSPEC void SDLCALL SDL_GetLogOutputFunction(SDL_LogOutputFunction
  * \param callback an SDL_LogOutputFunction to call instead of the default.
  * \param userdata a pointer that is passed to `callback`.
  *
+ * \threadsafety It is safe to call this function from any thread.
+ *
  * \since This function is available since SDL 3.0.0.
  *
  * \sa SDL_GetLogOutputFunction