Implement cooperative threads on hosted platforms using C code.

This replaces SDL threads with real cooperative threads, which are less cpu intensive and allow priority scheduling.
The backend for context switching is dependant on the host (sigaltstack/longjmp on Unix, Fibers on Windows).
configure has options to force or disallow SDL threads.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29327 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 58 insertions, 4 deletions

diff --git a/firmware/target/hosted/sdl/kernel-sdl.c b/firmware/target/hosted/sdl/kernel-sdl.c
index d933b9097e..4fb1aede0a 100644
--- a/firmware/target/hosted/sdl/kernel-sdl.c
+++ b/firmware/target/hosted/sdl/kernel-sdl.c
@@ -34,6 +34,14 @@
 static SDL_TimerID tick_timer_id;
 long start_tick;
 
+#ifndef HAVE_SDL_THREADS
+/* for the wait_for_interrupt function */
+static bool do_exit;
+static SDL_cond *wfi_cond;
+static SDL_mutex *wfi_mutex;
+#else
+#define do_exit false
+#endif
 /* Condition to signal that "interrupts" may proceed */
 static SDL_cond *sim_thread_cond;
 /* Mutex to serialize changing levels and exclude other threads while
@@ -98,6 +106,9 @@ void sim_exit_irq_handler(void)
 
     status_reg = 0;
     SDL_UnlockMutex(sim_irq_mtx);
+#ifndef HAVE_SDL_THREADS
+    SDL_CondSignal(wfi_cond);
+#endif
 }
 
 static bool sim_kernel_init(void)
@@ -115,15 +126,33 @@ static bool sim_kernel_init(void)
         panicf("Cannot create sim_thread_cond\n");
         return false;
     }
-
+#ifndef HAVE_SDL_THREADS
+    wfi_cond = SDL_CreateCond();
+    if (wfi_cond == NULL)
+    {
+        panicf("Cannot create wfi\n");
+        return false;
+    }
+    wfi_mutex = SDL_CreateMutex();
+    if (wfi_mutex == NULL)
+    {
+        panicf("Cannot create wfi mutex\n");
+        return false;
+    }
+#endif
     return true;
 }
 
 void sim_kernel_shutdown(void)
 {
     SDL_RemoveTimer(tick_timer_id);
+#ifndef HAVE_SDL_THREADS
+    do_exit = true;
+    SDL_CondSignal(wfi_cond);
+#endif
+    disable_irq(); 
     SDL_DestroyMutex(sim_irq_mtx);
-    SDL_DestroyCond(sim_thread_cond);
+    SDL_DestroyCond(sim_thread_cond); 
 }
 
 Uint32 tick_timer(Uint32 interval, void *param)
@@ -135,7 +164,7 @@ Uint32 tick_timer(Uint32 interval, void *param)
     
     new_tick = (SDL_GetTicks() - start_tick) / (1000/HZ);
         
-    while(new_tick != current_tick)
+    while(new_tick != current_tick && !do_exit)
     {
         sim_enter_irq_handler();
 
@@ -146,7 +175,7 @@ Uint32 tick_timer(Uint32 interval, void *param)
         sim_exit_irq_handler();
     }
     
-    return interval;
+    return do_exit ? 0 : interval;
 }
 
 void tick_start(unsigned int interval_in_ms)
@@ -168,4 +197,29 @@ void tick_start(unsigned int interval_in_ms)
     }
 
     tick_timer_id = SDL_AddTimer(interval_in_ms, tick_timer, NULL);
+#ifndef HAVE_SDL_THREADS
+    SDL_LockMutex(wfi_mutex);
+#endif
+}
+
+#ifndef HAVE_SDL_THREADS
+static void check_exit(void)
+{
+    if (UNLIKELY(do_exit))
+    {
+        SDL_DestroyCond(wfi_cond);
+        SDL_UnlockMutex(wfi_mutex);
+        SDL_DestroyMutex(wfi_mutex);
+        sim_do_exit();
+    }
+}
+
+void wait_for_interrupt(void)
+{
+    /* the exit may come at any time, during the CondWait or before,
+     * so check it twice */
+    check_exit();
+    SDL_CondWait(wfi_cond, wfi_mutex);
+    check_exit();
 }
+#endif