When SleepConditionVariableSRW() releases the SRW lock internally, it causes
our SDL_mutex_srw state to become inconsistent. The lock is unowned yet inside,
the owner is still the sleeping thread and more importantly the owner count is
still 1.
The next time someone acquires the lock, they will bump the owner count from 1
to 2. At that point, the lock is hosed. From the internal lock state, it looks
to us like that owner has acquired the lock recursively, even though they have
not. When they call SDL_UnlockMutex(), it will see the owner count > 0 and not
call ReleaseSRWLockExclusive().
Now when someone calls SDL_CondSignal(), SleepConditionVariableSRW() will start
the wakeup process by attempting to re-acquire the SRW lock. This will deadlock
because the lock was never released after the other thread had used it. The
thread waiting on the condition variable will never be able to wake up, even if
the SDL_CondWaitTimeout() function is used and the timeout expires.
Is automatically used when the SRW SDL_mutex implementation is active.
Otherwise falls back to the generic implementation.
v2: - Rebase onto master fa3ea1051a4b
Keep Semaphore Kernel Object impl for Windows 7 and older - choose at runtime
v2: - Fix mixed int/LONG types
- Reorder definitions
- Add missing include
v3: - Use `GetModuleHandle()` to load the API Set
v2: - Add SRW definitions as suggested by Ozkan Sezer
Allows building against older platform headers.
- Rename "hidden" function parameter `mutex_` to `_mutex`
v3: - Use GetModuleHandle instead of LoadLibrary
- Fix typo in comment
SDL_systhread.c and SDL_syslocale.c used to call LoadLibrary() without
calling FreeLibrary() later. GetModuleHandleW() should always succeed
because GetModuleHandleW() itself is imported from kernel32.dll and we
don't need to bother releasing it.
As the name suggests, the hint should only apply to SDL_THREAD_PRIORITY_TIME_CRITICAL
The resulting priorities for my current distro result in these values:
| High | Time Critical
Hint |--------------|-----------------
0 | P=10 N=-10 | P=5 N=-15
1 | P=10 N=-10 | P=-21 N=0
When we request realtime priority from rtkit, we have a rttime limit. If we exceed
that limit, the kernel will send SIGKILL to the process to terminate it.
This isn't something that most high priority processes will want, only processes
that selectively opt into SCHED_RR/FIFO through SDL_HINT_THREAD_PRIORITY_POLICY
should be subject to this level of scrutiny.
This change:
* Switches non-apple posix OSs to use SCHED_OTHER instead of SCHED_RR
for SDL_THREAD_PRIORITY_HIGH/SDL_THREAD_PRIORITY_TIME_CRITICAL.
* Fixes using a hardcoded RLIMIT_RTTIME, instead queries it from rtkit
* Only sets RLIMIT_RTTIME for MakeRealtime rtkit requests
* Adds a note regarding the possible SIGKILL with SDL_HINT_THREAD_PRIORITY_POLICY
* Introduces SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL to allow apps to acquire realtime scheduling policies on Linux
- video: VideoBootStrap->available() is gone.
- thread: all important SDL_CreateThread internal data now put into
struct SDL_Thread: changes to SDL_SYS_CreateThread().
1. Comment that SDL_SetThreadPriority will make any necessary system changes when applying priority.
2. Add a hint to override SDL's default behavior for scheduler policy.
3. Modify the pthreads SDL_SetThreadPriority so that instead of just using the current thread scheduler policy it will change it to a policy that should work best for the requested priority.
4. Add hint checks in SDL_SetThreadPriority so that #3 can be overridden if desired.
5. Modify the Linux SDL_SetThreadPriority so that in the case that policy, either by SDL defaults or from the hint, is a realtime policy it uses the realtime rtkit API.
6. Prior to calling rtkit on Linux make the necessary thread state changes that rtkit requires. Currently this is done every time as it isn't expected that SDL_SetThreadPriority will be called repeatedly for a thread.
This avoids the need to malloc something extra, use a semaphore, etc, and
fixes Emscripten with pthreads support, which might not spin up a web worker
until after SDL_CreateThread returns and thus can't wait on a semaphore at
this point in any case.
Fixes Bugzilla #5064.
Ethan Lee
Attached is a diff that I used to get SetThreadPriority working locally. I still have no idea what the minimum SDK version is since Microsoft never documented it, but it's worth pointing out that they're much more aggressive about using the latest VS and UWP SDK anyway (for example, an updated Xbox is no longer compatible with VS2017, and updates are required to have a network connection of any kind).
Christian Herzig
pthread_mutex_trylock() and by the way, pthread_mutex_lock() do not set errno.
Pthread-methods directly return error code as int. See related man-pages for
details.
