From f521b22eb509b3f436b9af9441185430a7627d1e Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Mon, 23 Apr 2018 22:07:56 -0700
Subject: [PATCH] Added SDL_THREAD_PRIORITY_TIME_CRITICAL

---
 include/SDL_thread.h               | 5 +++--
 src/audio/SDL_audio.c              | 2 +-
 src/thread/psp/SDL_systhread.c     | 2 ++
 src/thread/pthread/SDL_systhread.c | 7 ++++++-
 src/thread/windows/SDL_systhread.c | 2 ++
 test/testthread.c                  | 3 ++-
 6 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/include/SDL_thread.h b/include/SDL_thread.h
index 82a43fc032af0..5d01d5a52c86f 100644
--- a/include/SDL_thread.h
+++ b/include/SDL_thread.h
@@ -54,12 +54,13 @@ typedef unsigned int SDL_TLSID;
 /**
  *  The SDL thread priority.
  *
- *  \note On many systems you require special privileges to set high priority.
+ *  \note On many systems you require special privileges to set high or time critical priority.
  */
 typedef enum {
     SDL_THREAD_PRIORITY_LOW,
     SDL_THREAD_PRIORITY_NORMAL,
-    SDL_THREAD_PRIORITY_HIGH
+    SDL_THREAD_PRIORITY_HIGH,
+    SDL_THREAD_PRIORITY_TIME_CRITICAL
 } SDL_ThreadPriority;
 
 /**
diff --git a/src/audio/SDL_audio.c b/src/audio/SDL_audio.c
index 50ce43cb9f197..364e25e3ca63f 100644
--- a/src/audio/SDL_audio.c
+++ b/src/audio/SDL_audio.c
@@ -651,7 +651,7 @@ SDL_RunAudio(void *devicep)
     SDL_assert(!device->iscapture);
 
     /* The audio mixing is always a high priority thread */
-    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_HIGH);
+    SDL_SetThreadPriority(SDL_THREAD_PRIORITY_TIME_CRITICAL);
 
     /* Perform any thread setup */
     device->threadid = SDL_ThreadID();
diff --git a/src/thread/psp/SDL_systhread.c b/src/thread/psp/SDL_systhread.c
index 9286be59e23bc..284f182a6a299 100644
--- a/src/thread/psp/SDL_systhread.c
+++ b/src/thread/psp/SDL_systhread.c
@@ -97,6 +97,8 @@ int SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
     if (priority == SDL_THREAD_PRIORITY_LOW) {
         value = 19;
     } else if (priority == SDL_THREAD_PRIORITY_HIGH) {
+        value = -10;
+    } else if (priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
         value = -20;
     } else {
         value = 0;
diff --git a/src/thread/pthread/SDL_systhread.c b/src/thread/pthread/SDL_systhread.c
index adb7b77bc70cc..4842d9c80be44 100644
--- a/src/thread/pthread/SDL_systhread.c
+++ b/src/thread/pthread/SDL_systhread.c
@@ -275,6 +275,8 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
     if (priority == SDL_THREAD_PRIORITY_LOW) {
         value = 19;
     } else if (priority == SDL_THREAD_PRIORITY_HIGH) {
+        value = -10;
+    } else if (priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
         value = -20;
     } else {
         value = 0;
@@ -290,12 +292,15 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
     }
     if (priority == SDL_THREAD_PRIORITY_LOW) {
         sched.sched_priority = sched_get_priority_min(policy);
-    } else if (priority == SDL_THREAD_PRIORITY_HIGH) {
+    } else if (priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
         sched.sched_priority = sched_get_priority_max(policy);
     } else {
         int min_priority = sched_get_priority_min(policy);
         int max_priority = sched_get_priority_max(policy);
         sched.sched_priority = (min_priority + (max_priority - min_priority) / 2);
+        if (priority == SDL_THREAD_PRIORITY_HIGH) {
+            sched.sched_priority += (max_priority - min_priority) / 4);
+        }
     }
     if (pthread_setschedparam(thread, policy, &sched) != 0) {
         return SDL_SetError("pthread_setschedparam() failed");
diff --git a/src/thread/windows/SDL_systhread.c b/src/thread/windows/SDL_systhread.c
index 90036c92077e1..251510d48035d 100644
--- a/src/thread/windows/SDL_systhread.c
+++ b/src/thread/windows/SDL_systhread.c
@@ -231,6 +231,8 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
         value = THREAD_PRIORITY_LOWEST;
     } else if (priority == SDL_THREAD_PRIORITY_HIGH) {
         value = THREAD_PRIORITY_HIGHEST;
+    } else if (priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
+        value = THREAD_PRIORITY_TIME_CRITICAL;
     } else {
         value = THREAD_PRIORITY_NORMAL;
     }
diff --git a/test/testthread.c b/test/testthread.c
index efba681e8a6c4..4555a1e945747 100644
--- a/test/testthread.c
+++ b/test/testthread.c
@@ -38,6 +38,7 @@ getprioritystr(SDL_ThreadPriority priority)
     case SDL_THREAD_PRIORITY_LOW: return "SDL_THREAD_PRIORITY_LOW";
     case SDL_THREAD_PRIORITY_NORMAL: return "SDL_THREAD_PRIORITY_NORMAL";
     case SDL_THREAD_PRIORITY_HIGH: return "SDL_THREAD_PRIORITY_HIGH";
+    case SDL_THREAD_PRIORITY_TIME_CRITICAL: return "SDL_THREAD_PRIORITY_TIME_CRITICAL";
     }
 
     return "???";
@@ -56,7 +57,7 @@ ThreadFunc(void *data)
 
         if (testprio) {
             SDL_Log("SDL_SetThreadPriority(%s):%d\n", getprioritystr(prio), SDL_SetThreadPriority(prio));
-            if (++prio > SDL_THREAD_PRIORITY_HIGH)
+            if (++prio > SDL_THREAD_PRIORITY_TIME_CRITICAL)
                 prio = SDL_THREAD_PRIORITY_LOW;
         }