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Fix process randomly getting killed when SDL_THREAD_PRIORITY_HIGH/TIME_CRITICAL is set

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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
This commit is contained in:
Sam Lantinga
2020-11-11 08:47:18 -08:00
parent 59795822d0
commit 07eae7d670
3 changed files with 41 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
src/thread/pthread/SDL_systhread.c
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@@ -208,6 +208,7 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
int pri_policy;
pthread_t thread = pthread_self();
const char *policyhint = SDL_GetHint(SDL_HINT_THREAD_PRIORITY_POLICY);
const SDL_bool allow_realtime_hint = SDL_GetHintBoolean(SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL, SDL_FALSE);
if (pthread_getschedparam(thread, &policy, &sched) != 0) {
return SDL_SetError("pthread_getschedparam() failed");
@@ -223,8 +224,14 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
break;
case SDL_THREAD_PRIORITY_HIGH:
case SDL_THREAD_PRIORITY_TIME_CRITICAL:
#if defined(__MACOSX__) || defined(__IPHONEOS__) || defined(__TVOS__)
/* Apple requires SCHED_RR for high priority threads */
pri_policy = SCHED_RR;
break;
#else
pri_policy = allow_realtime_hint ? SCHED_RR : SCHED_OTHER;
break;
#endif
default:
pri_policy = policy;
break;