Removed external hashtable locking functions

Read-write locks are not recursive and can't be upgraded from one type to another, so it's not safe to lock the hash table and then call functions that operate on it. If you really want this functionality, we'd need to create unlocked versions of the hashtable functions and you would call those once you've taken a lock on the hashtable, and we'd have to assert that the operations you're doing are compatible with the type of lock you've taken.

All of that complicates working with hashtables, so if you need that type of access, you should probably just use external locking.

src/stdlib/SDL_getenv.c

@@ -53,6 +53,7 @@ static char **environ;
 
 struct SDL_Environment
 {
+    SDL_Mutex *lock;
     SDL_HashTable *strings;
 };
 static SDL_Environment *SDL_environment;
@@ -87,12 +88,15 @@ SDL_Environment *SDL_CreateEnvironment(bool populated)
         return NULL;
     }
 
-    env->strings = SDL_CreateHashTable(NULL, 16, SDL_HashString, SDL_KeyMatchString, SDL_NukeFreeKey, true, false);
+    env->strings = SDL_CreateHashTable(NULL, 16, SDL_HashString, SDL_KeyMatchString, SDL_NukeFreeKey, false, false);
     if (!env->strings) {
         SDL_free(env);
         return NULL;
     }
 
+    // Don't fail if we can't create a mutex (e.g. on a single-thread environment)
+    env->lock = SDL_CreateMutex();
+
     if (populated) {
 #ifdef SDL_PLATFORM_WINDOWS
         LPWCH strings = GetEnvironmentStringsW();
@@ -153,10 +157,15 @@ const char *SDL_GetEnvironmentVariable(SDL_Environment *env, const char *name)
         return NULL;
     }
 
-    const char *value;
-    if (SDL_FindInHashTable(env->strings, name, (const void **)&value)) {
-        result = SDL_GetPersistentString(value);
+    SDL_LockMutex(env->lock);
+    {
+        const char *value;
+
+        if (SDL_FindInHashTable(env->strings, name, (const void **)&value)) {
+            result = SDL_GetPersistentString(value);
+        }
     }
+    SDL_UnlockMutex(env->lock);
 
     return result;
 }
@@ -170,7 +179,7 @@ char **SDL_GetEnvironmentVariables(SDL_Environment *env)
         return NULL;
     }
 
-    SDL_LockHashTable(env->strings, false);
+    SDL_LockMutex(env->lock);
     {
         size_t count, length = 0;
         void *iter;
@@ -207,7 +216,7 @@ char **SDL_GetEnvironmentVariables(SDL_Environment *env)
         }
         result[count] = NULL;
     }
-    SDL_UnlockHashTable(env->strings);
+    SDL_UnlockMutex(env->lock);
 
     return result;
 }
@@ -224,7 +233,7 @@ bool SDL_SetEnvironmentVariable(SDL_Environment *env, const char *name, const ch
         return SDL_InvalidParamError("value");
     }
 
-    SDL_LockHashTable(env->strings, true);
+    SDL_LockMutex(env->lock);
     {
         const void *existing_value;
         bool insert = true;
@@ -249,21 +258,33 @@ bool SDL_SetEnvironmentVariable(SDL_Environment *env, const char *name, const ch
             }
         }
     }
-    SDL_UnlockHashTable(env->strings);
+    SDL_UnlockMutex(env->lock);
 
     return result;
 }
 
 bool SDL_UnsetEnvironmentVariable(SDL_Environment *env, const char *name)
 {
+    bool result = false;
+
     if (!env) {
         return SDL_InvalidParamError("env");
     } else if (!name || *name == '\0' || SDL_strchr(name, '=') != NULL) {
         return SDL_InvalidParamError("name");
     }
 
-    SDL_RemoveFromHashTable(env->strings, name);
-    return true;
+    SDL_LockMutex(env->lock);
+    {
+        const void *value;
+        if (SDL_FindInHashTable(env->strings, name, &value)) {
+            result = SDL_RemoveFromHashTable(env->strings, name);
+        } else {
+            result = true;
+        }
+    }
+    SDL_UnlockMutex(env->lock);
+
+    return result;
 }
 
 void SDL_DestroyEnvironment(SDL_Environment *env)
@@ -272,6 +293,7 @@ void SDL_DestroyEnvironment(SDL_Environment *env)
         return;
     }
 
+    SDL_DestroyMutex(env->lock);
     SDL_DestroyHashTable(env->strings);
     SDL_free(env);
 }