kc3-lang/SDL

diff --git a/include/SDL_hints.h b/include/SDL_hints.h
index a9dbbae..24b9022 100644
--- a/include/SDL_hints.h
+++ b/include/SDL_hints.h
@@ -799,10 +799,33 @@ 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)
  */
 #define SDL_HINT_VIDEO_HIGHDPI_DISABLED "SDL_VIDEO_HIGHDPI_DISABLED"
diff --git a/src/core/linux/SDL_threadprio.c b/src/core/linux/SDL_threadprio.c
index 275c15c..5b1835c 100644
--- a/src/core/linux/SDL_threadprio.c
+++ b/src/core/linux/SDL_threadprio.c
@@ -50,6 +50,7 @@
 static pthread_once_t rtkit_initialize_once = PTHREAD_ONCE_INIT;
 static Sint32 rtkit_min_nice_level = -20;
 static Sint32 rtkit_max_realtime_priority = 99;
+static Sint64 rtkit_max_rttime_usec = 200000;
 
 static void
 rtkit_initialize()
@@ -67,10 +68,16 @@ rtkit_initialize()
                                             DBUS_TYPE_INT32, &rtkit_max_realtime_priority)) {
         rtkit_max_realtime_priority = 99;
     }
+
+    /* Try getting maximum rttime allowed by rtkit: exceeding this value will result in SIGKILL */
+    if (!dbus || !SDL_DBus_QueryPropertyOnConnection(dbus->system_conn, RTKIT_DBUS_NODE, RTKIT_DBUS_PATH, RTKIT_DBUS_INTERFACE, "RTTimeUSecMax",
+                                            DBUS_TYPE_INT64, &rtkit_max_rttime_usec)) {
+        rtkit_max_rttime_usec = 200000;
+    }
 }
 
 static SDL_bool
-rtkit_initialize_thread()
+rtkit_initialize_realtime_thread()
 {
     // Following is an excerpt from rtkit README that outlines the requirements
     // a thread must meet before making rtkit requests:
@@ -107,7 +114,8 @@ rtkit_initialize_thread()
     }
 
     // Current rtkit allows a max of 200ms right now
-    rlimit.rlim_cur = rlimit.rlim_max = 100000;
+    rlimit.rlim_max = rtkit_max_rttime_usec;
+    rlimit.rlim_cur = rlimit.rlim_max / 2;
     err = setrlimit(nLimit, &rlimit);
     if (err)
     {
@@ -142,14 +150,6 @@ rtkit_setpriority_nice(pid_t thread, int nice_level)
     if (si32 < rtkit_min_nice_level)
         si32 = rtkit_min_nice_level;
 
-    // We always perform the thread state changes necessary for rtkit.
-    // This wastes some system calls if the state is already set but
-    // typically code sets a thread priority and leaves it so it's
-    // not expected that this wasted effort will be an issue.
-    // We also do not quit if this fails, we let the rtkit request
-    // go through to determine whether it really needs to fail or not.
-    rtkit_initialize_thread();
-
     if (!dbus || !SDL_DBus_CallMethodOnConnection(dbus->system_conn,
             RTKIT_DBUS_NODE, RTKIT_DBUS_PATH, RTKIT_DBUS_INTERFACE, "MakeThreadHighPriority",
             DBUS_TYPE_UINT64, &ui64, DBUS_TYPE_INT32, &si32, DBUS_TYPE_INVALID,
@@ -177,7 +177,7 @@ rtkit_setpriority_realtime(pid_t thread, int rt_priority)
     // not expected that this wasted effort will be an issue.
     // We also do not quit if this fails, we let the rtkit request
     // go through to determine whether it really needs to fail or not.
-    rtkit_initialize_thread();
+    rtkit_initialize_realtime_thread();
 
     if (!dbus || !SDL_DBus_CallMethodOnConnection(dbus->system_conn,
             RTKIT_DBUS_NODE, RTKIT_DBUS_PATH, RTKIT_DBUS_INTERFACE, "MakeThreadRealtime",
diff --git a/src/thread/pthread/SDL_systhread.c b/src/thread/pthread/SDL_systhread.c
index 6df049c..b6cd04a 100644
--- a/src/thread/pthread/SDL_systhread.c
+++ b/src/thread/pthread/SDL_systhread.c
@@ -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;