Add thread priority API

Expose an API to change the priority of the current thread.

app/src/compat.h

@@ -54,6 +54,10 @@
 # define SCRCPY_SDL_HAS_HINT_VIDEO_X11_NET_WM_BYPASS_COMPOSITOR
 #endif
 
+#if SDL_VERSION_ATLEAST(2, 0, 16)
+# define SCRCPY_SDL_HAS_THREAD_PRIORITY_TIME_CRITICAL
+#endif
+
 #ifndef HAVE_STRDUP
 char *strdup(const char *s);
 #endif

app/src/util/thread.c

@@ -23,6 +23,39 @@ sc_thread_create(sc_thread *thread, sc_thread_fn fn, const char *name,
     return true;
 }
 
+static SDL_ThreadPriority
+to_sdl_thread_priority(enum sc_thread_priority priority) {
+    switch (priority) {
+        case SC_THREAD_PRIORITY_TIME_CRITICAL:
+#ifdef SCRCPY_SDL_HAS_THREAD_PRIORITY_TIME_CRITICAL
+            return SDL_THREAD_PRIORITY_TIME_CRITICAL;
+#else
+            // fall through
+#endif
+        case SC_THREAD_PRIORITY_HIGH:
+            return SDL_THREAD_PRIORITY_HIGH;
+        case SC_THREAD_PRIORITY_NORMAL:
+            return SDL_THREAD_PRIORITY_NORMAL;
+        case SC_THREAD_PRIORITY_LOW:
+            return SDL_THREAD_PRIORITY_LOW;
+        default:
+            assert(!"Unknown thread priority");
+            return 0;
+    }
+}
+
+bool
+sc_thread_set_priority(enum sc_thread_priority priority) {
+    SDL_ThreadPriority sdl_priority = to_sdl_thread_priority(priority);
+    int r = SDL_SetThreadPriority(sdl_priority);
+    if (r) {
+        LOGD("Could not set thread priority: %s", SDL_GetError());
+        return false;
+    }
+
+    return true;
+}
+
 void
 sc_thread_join(sc_thread *thread, int *status) {
     SDL_WaitThread(thread->thread, status);

app/src/util/thread.h

@@ -21,6 +21,13 @@ typedef struct sc_thread {
     SDL_Thread *thread;
 } sc_thread;
 
+enum sc_thread_priority {
+    SC_THREAD_PRIORITY_LOW,
+    SC_THREAD_PRIORITY_NORMAL,
+    SC_THREAD_PRIORITY_HIGH,
+    SC_THREAD_PRIORITY_TIME_CRITICAL,
+};
+
 typedef struct sc_mutex {
     SDL_mutex *mutex;
 #ifndef NDEBUG
@@ -39,6 +46,9 @@ sc_thread_create(sc_thread *thread, sc_thread_fn fn, const char *name,
 void
 sc_thread_join(sc_thread *thread, int *status);
 
+bool
+sc_thread_set_priority(enum sc_thread_priority priority);
+
 bool
 sc_mutex_init(sc_mutex *mutex);