From 8f6397bf0710174d701514c38d9ffe19c752d9e8 Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@ubuntu-12-64.(none)>
Date: Fri, 2 Nov 2012 12:56:09 -0600
Subject: [PATCH] fix locking for futures on uniprocessors

The scheme_is_multiprocessor() function wasn't the right guard
for whether to use a locking compare-and-swap instruction; any
use of pthread-based futures needs the compare-and-swap.

Merge to v5.3.1
(cherry picked from commit 55170581c4179d37d42c6e0975b290ee08dd14d0)
---
 src/racket/src/future.c    | 19 ++++++++-----------
 src/racket/src/hash.c      |  4 +---
 src/racket/src/jitcommon.c |  4 ++--
 src/racket/src/jitinline.c |  2 +-
 src/racket/src/schpriv.h   |  2 +-
 5 files changed, 13 insertions(+), 18 deletions(-)

diff --git a/src/racket/src/future.c b/src/racket/src/future.c
index 58babfef63..a6d283544d 100644
--- a/src/racket/src/future.c
+++ b/src/racket/src/future.c
@@ -156,7 +156,7 @@ static Scheme_Object *processor_count(int argc, Scheme_Object *argv[])
   return scheme_make_integer(1);
 }
 
-int scheme_is_multiprocessor(int now)
+int scheme_is_multithreaded(int now)
 {
   return 0;
 }
@@ -2185,17 +2185,14 @@ static void init_cpucount(void)
 #endif
 }
 
-int scheme_is_multiprocessor(int now)
+int scheme_is_multithreaded(int now)
 {
-  if (cpucount > 1) {
-    if (!now) 
-      return 1;
-    else {
-      Scheme_Future_State *fs = scheme_future_state;
-      return (fs && fs->future_threads_created);
-    }
-  } else
-    return 0;
+  if (!now)
+    return 1;
+  else {
+    Scheme_Future_State *fs = scheme_future_state;
+    return (fs && fs->future_threads_created);
+  }
 }
 
 Scheme_Object *processor_count(int argc, Scheme_Object *argv[])
diff --git a/src/racket/src/hash.c b/src/racket/src/hash.c
index 3df6636489..58ebf57d30 100644
--- a/src/racket/src/hash.c
+++ b/src/racket/src/hash.c
@@ -61,8 +61,6 @@ static void register_traversers(void);
    running in a future and setting flags on pairs. */
 SHARED_OK static uintptr_t keygen;
 
-XFORM_NONGCING extern int scheme_is_multiprocessor();
-
 XFORM_NONGCING static MZ_INLINE
 uintptr_t PTR_TO_LONG(Scheme_Object *o)
 {
@@ -92,7 +90,7 @@ uintptr_t PTR_TO_LONG(Scheme_Object *o)
 #endif
     if (!v) v = 0x1AD0;
 #ifdef MZ_USE_FUTURES
-    if (SCHEME_PAIRP(o) && scheme_is_multiprocessor(1)) {
+    if (SCHEME_PAIRP(o) && scheme_is_multithreaded(1)) {
       /* Use CAS to avoid losing a hash code due to a conflict with
          JIT-generated `list?' test, which itself uses CAS to set "is
          a list" or "not a list" flags on pairs. */
diff --git a/src/racket/src/jitcommon.c b/src/racket/src/jitcommon.c
index b2fa5444eb..1bf70cf146 100644
--- a/src/racket/src/jitcommon.c
+++ b/src/racket/src/jitcommon.c
@@ -2349,7 +2349,7 @@ static int common7(mz_jit_state *jitter, void *_data)
 
     jit_ldxi_s(JIT_R2, JIT_R1, &MZ_OPT_HASH_KEY(&((Scheme_Stx *)0x0)->iso));
 #ifdef MZ_USE_FUTURES
-    if (scheme_is_multiprocessor(0)) {
+    if (scheme_is_multithreaded(0)) {
       /* Need an atomic update in case another thread is setting
          a hash code on the target pair. */
       ref5 = jit_bmsi_i(jit_forward(), JIT_R2, PAIR_IS_LIST);
@@ -2386,7 +2386,7 @@ static int common7(mz_jit_state *jitter, void *_data)
     jit_ldxi_s(JIT_R2, JIT_R1, &MZ_OPT_HASH_KEY(&((Scheme_Stx *)0x0)->iso));
 #ifdef MZ_USE_FUTURES
     /* As above: */
-    if (scheme_is_multiprocessor(0)) {
+    if (scheme_is_multithreaded(0)) {
       ref5 = jit_bmsi_i(jit_forward(), JIT_R2, PAIR_IS_NON_LIST);
       jit_movr_i(JIT_R0, JIT_R2);
       jit_ori_i(JIT_R2, JIT_R2, PAIR_IS_NON_LIST);
diff --git a/src/racket/src/jitinline.c b/src/racket/src/jitinline.c
index c14af07bec..45f3257401 100644
--- a/src/racket/src/jitinline.c
+++ b/src/racket/src/jitinline.c
@@ -2883,7 +2883,7 @@ int scheme_generate_inlined_nary(mz_jit_state *jitter, Scheme_App_Rec *app, int
 
     /* This is the actual CAS: */
 #ifdef MZ_USE_FUTURES
-    if (scheme_is_multiprocessor(0)) {
+    if (scheme_is_multithreaded(0)) {
       jit_lock_cmpxchgr_l(JIT_R1, JIT_V1); /* implicitly uses JIT_R0 */
       reffalse = (JNEm(jit_forward(), 0,0,0), _jit.x.pc);
     } else
diff --git a/src/racket/src/schpriv.h b/src/racket/src/schpriv.h
index e924d9476b..547bad1b46 100644
--- a/src/racket/src/schpriv.h
+++ b/src/racket/src/schpriv.h
@@ -303,7 +303,7 @@ void scheme_free_dynamic_extensions(void);
 void scheme_free_all_code(void);
 void scheme_free_ghbn_data(void);
 
-XFORM_NONGCING int scheme_is_multiprocessor(int now);
+XFORM_NONGCING int scheme_is_multithreaded(int now);
 
 /* Type readers & writers for compiled code data */
 typedef Scheme_Object *(*Scheme_Type_Reader)(Scheme_Object *list);