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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
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23
include/SDL_hints.h
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@ -799,9 +799,32 @@ extern "C" {
*
* pthread hint values are "current", "other", "fifo" and "rr".
* Currently no other platform hint values are defined but may be in the future.
*
* \note On Linux, the kernel may send SIGKILL to realtime tasks which exceed the distro
* configured execution budget for rtkit. This budget is queriably through RLIMIT_RTTIME
* after calling SDL_SetThreadPriority().
*/
#define SDL_HINT_THREAD_PRIORITY_POLICY "SDL_THREAD_PRIORITY_POLICY"
/**
* \brief Specifies whether SDL_THREAD_PRIORITY_TIME_CRITICAL should be treated as realtime.
*
* On some platforms, like Linux, a realtime priority thread may be subject to restrictions
* that require special handling by the application. This hint exists to let SDL know that
* the app is prepared to handle said restrictions.
*
* On Linux, SDL will apply the following configuration to any thread that becomes realtime:
* * The SCHED_RESET_ON_FORK bit will be set on the scheduling policy,
* * An RLIMIT_RTTIME budget will be configured to the rtkit specified limit.
* * Exceeding this limit will result in the kernel sending SIGKILL to the app,
* * Refer to the man pages for more information.
*
* This variable can be set to the following values:
* "0" - default platform specific behaviour
* "1" - Force SDL_THREAD_PRIORITY_TIME_CRITICAL to a realtime scheduling policy
*/
#define SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL "SDL_THREAD_FORCE_REALTIME_TIME_CRITICAL"
/**
* \brief If set to 1, then do not allow high-DPI windows. ("Retina" on Mac and iOS)
*/