From 7c0c1e80ceb5c555003341ec0ced80d3ef9b990a Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Mon, 7 Feb 2011 22:57:33 -0800
Subject: [PATCH] It's now possible to disable the fast atomic operations, at a
 huge performance penalty.

---
 configure.in              |  6 ++++++
 include/SDL_atomic.h      |  3 +++
 include/SDL_config.h.in   |  1 +
 src/atomic/SDL_spinlock.c | 21 ++++++++++++++++++++-
 4 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/configure.in b/configure.in
index f0d3ac58e..252f15f46 100644
--- a/configure.in
+++ b/configure.in
@@ -422,6 +422,12 @@ AC_HELP_STRING([--enable-cpuinfo], [Enable the cpuinfo subsystem [[default=yes]]
 if test x$enable_cpuinfo != xyes; then
     AC_DEFINE(SDL_CPUINFO_DISABLED)
 fi
+AC_ARG_ENABLE(atomic,
+AC_HELP_STRING([--enable-atomic], [Enable the atomic operations [[default=yes]]]),
+              , enable_atomic=yes)
+if test x$enable_atomic != xyes; then
+    AC_DEFINE(SDL_ATOMIC_DISABLED)
+fi
 AC_ARG_ENABLE(assembly,
 AC_HELP_STRING([--enable-assembly], [Enable assembly routines [[default=yes]]]),
               , enable_assembly=yes)
diff --git a/include/SDL_atomic.h b/include/SDL_atomic.h
index e7af7269a..236ee861e 100644
--- a/include/SDL_atomic.h
+++ b/include/SDL_atomic.h
@@ -141,6 +141,9 @@ void _ReadWriteBarrier(void);
 /* Platform specific optimized versions of the atomic functions,
  * you can disable these by defining SDL_DISABLE_ATOMIC_INLINE
  */
+#if SDL_ATOMIC_DISABLED
+#define SDL_DISABLE_ATOMIC_INLINE
+#endif
 #ifndef SDL_DISABLE_ATOMIC_INLINE
 
 #ifdef HAVE_MSC_ATOMICS
diff --git a/include/SDL_config.h.in b/include/SDL_config.h.in
index 70b540fc2..551ceb6ad 100644
--- a/include/SDL_config.h.in
+++ b/include/SDL_config.h.in
@@ -171,6 +171,7 @@
 #undef SDL_DEFAULT_ASSERT_LEVEL
 
 /* Allow disabling of core subsystems */
+#undef SDL_ATOMIC_DISABLED
 #undef SDL_AUDIO_DISABLED
 #undef SDL_CPUINFO_DISABLED
 #undef SDL_EVENTS_DISABLED
diff --git a/src/atomic/SDL_spinlock.c b/src/atomic/SDL_spinlock.c
index 83ba93727..9eb03b319 100644
--- a/src/atomic/SDL_spinlock.c
+++ b/src/atomic/SDL_spinlock.c
@@ -22,6 +22,7 @@
 #include "SDL_stdinc.h"
 
 #include "SDL_atomic.h"
+#include "SDL_mutex.h"
 #include "SDL_timer.h"
 
 /* Don't do the check for Visual Studio 2005, it's safe here */
@@ -33,7 +34,25 @@
 SDL_bool
 SDL_AtomicTryLock(SDL_SpinLock *lock)
 {
-#if defined(_MSC_VER)
+#if SDL_ATOMIC_DISABLED
+    /* Terrible terrible damage */
+    static SDL_mutex *_spinlock_mutex;
+
+    if (!_spinlock_mutex) {
+        /* Race condition on first lock... */
+        _spinlock_mutex = SDL_CreateMutex();
+    }
+    SDL_mutexP(_spinlock_mutex);
+    if (*lock == 0) {
+        *lock = 1;
+        SDL_mutexV(_spinlock_mutex);
+        return SDL_TRUE;
+    } else {
+        SDL_mutexV(_spinlock_mutex);
+        return SDL_FALSE;
+    }
+
+#elif defined(_MSC_VER)
     SDL_COMPILE_TIME_ASSERT(locksize, sizeof(*lock) == sizeof(long));
     return (InterlockedExchange((long*)lock, 1) == 0);