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Add an invalid #define for SDL_ThreadID() to SDL_oldnames.h (#15801)

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in SDL2 SDL_ThreadID() was a function that's now
SDL_GetCurrentThreadID(), but in SDL3 SDL_ThreadID is a type, so
in C++ `x = SDL_ThreadID()` is valid code (default constructor which
in case of integers means 0), so that's a massive footgun.

See the big comment in SDL_oldnames.h for more details.

Added `#undef SDL_ThreadID` in SDL_dynapi.c because it has one of the
(quite rare) cases  where "SDL_ThreadID" followed by a "(" is actually
correct and necessary (function pointer returning SDL_ThreadID).
This commit is contained in:
Daniel Gibson
2026-06-12 19:24:56 +02:00
committed by GitHub
parent 4f031ea5da
commit b04d026458
3 changed files with 71 additions and 0 deletions
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11
docs/README-migration.md
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@@ -41,6 +41,8 @@ Many functions and symbols have been renamed. We have provided a handy Python sc
rename_symbols.py --all-symbols source_code_path
```
**Note** that `rename_symbols.py` can't completely handle `SDL_ThreadID`, see the [SDL_Thread.h section](#sdl_threadh) below.
It's also possible to apply a semantic patch to migrate more easily to SDL3: [SDL_migration.cocci](https://github.com/libsdl-org/SDL/blob/main/build-scripts/SDL_migration.cocci)
SDL headers should now be included as `#include <SDL3/SDL.h>`. Typically that's the only SDL header you'll need in your application unless you are using OpenGL or Vulkan functionality. SDL_image, SDL_mixer, SDL_net, SDL_ttf and SDL_rtf have also their preferred include path changed: for SDL_image, it becomes `#include <SDL3_image/SDL_image.h>`. We have provided a handy Python script [rename_headers.py](https://github.com/libsdl-org/SDL/blob/main/build-scripts/rename_headers.py) to rename SDL2 headers to their SDL3 counterparts:
@@ -2046,6 +2048,15 @@ The following functions have been removed:
The following symbols have been renamed:
* SDL_threadID => SDL_ThreadID
### Attention: Potential problems with `SDL_ThreadID`
**_`SDL_ThreadID`_** is a case that needs **special attention**, because if you forget to rename a call to `SDL_ThreadID()` to `SDL_GetCurrentThreadID()` in **C++** code, it will *still compile fine*, calling the default constructor of the `SDL_ThreadID` type, initializing it to `0` - but if `SDL_GetCurrentThreadID()` was intended, that of course leads to **wrong behavior** that can be hard to catch.
Furthermore **`rename_symbols.py` does not handle it** (because it would be hard to do in a way that doesn't break anything when running that script twice), which makes it even more error-prone.
SDL_oldnames.h now has a `#define` that should catch these cases, but it's not available in SDL 3.4.10 and older. So if you're using 3.4.10 or older, check your code carefully for occurences of `SDL_ThreadID()` and make sure it wasn't supposed to be `SDL_GetCurrentThreadID()`.
In some edge cases this `#define` can cause false positives (compile errors even though `SDL_ThreadID` was used correctly); right above that definition in the header is a long comment explaining possible problems and solutions.
## SDL_timer.h
SDL_GetTicks() now returns a 64-bit value. Instead of using the SDL_TICKS_PASSED macro, you can directly compare tick values, e.g.