Add memory barriers to full/empty bit manipulations to fix synchroniz…

…ation bugs.
stingergraph · Nov 22, 2016 · b6f65df · b6f65df
1 parent 0eb1f54
commit b6f65df
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Showing 2 changed files with 27 additions and 3 deletions.
diff --git a/lib/stinger_core/inc/stinger_atomics.h b/lib/stinger_core/inc/stinger_atomics.h
@@ -9,6 +9,7 @@ extern "C" {
 
 #include "stinger.h"
 
+static inline void stinger_memory_barrier();
 static inline int stinger_int_fetch_add (int *, int);
 static inline int64_t stinger_int64_fetch_add (int64_t *, int64_t);
 static inline uint64_t stinger_uint64_fetch_add (uint64_t *, uint64_t);
@@ -26,6 +27,12 @@ static inline void *stinger_ptr_cas (void **, void *, void *);
 
 #if defined(__GNUC__)||defined(__INTEL_COMPILER)
 /* {{{ GCC / ICC defs */
+void
+stinger_memory_barrier()
+{
+  __sync_synchronize();
+}
+
 int
 stinger_int_fetch_add (int *x, int i)
 {
@@ -87,6 +94,12 @@ stinger_int64_cas (int64_t * x, int64_t origx, int64_t newx)
 /* }}} */
 #elif defined(__xlc__)
 /* {{{ XLC defs */
+void
+stinger_memory_barrier()
+{
+  __sync_synchronize();
+}
+
 int
 stinger_int_fetch_add (int *x, int i)
 {
@@ -153,6 +166,11 @@ stinger_int64_cas (int64_t * x, int64_t origx, int64_t newx)
 #elif !defined(_OPENMP)
 #warning "Assuming no parallel / concurrent operations necessary."
 /* {{{ Not concurrent */
+void
+stinger_memory_barrier()
+{
+}
+
 int
 stinger_int_fetch_add (int *v, int x)
 {

diff --git a/lib/stinger_core/src/x86_full_empty.c b/lib/stinger_core/src/x86_full_empty.c
@@ -1,8 +1,8 @@
 /* x86 Emulation of Full Empty Bits Using atomic check-and-swap.
  *
  * NOTES:
- * - Using these functions means that the MARKER value defined 
- *   below must be reserved in your application and CANNOT be 
+ * - Using these functions means that the MARKER value defined
+ *   below must be reserved in your application and CANNOT be
  *   considered a normal value.  Feel free to change the value to
  *   suit your application.
  * - Do not compile this file with optimization.  There are loops
@@ -15,8 +15,9 @@
 
 #include  "x86_full_empty.h"
 
-uint64_t 
+uint64_t
 readfe(volatile uint64_t * v) {
+  stinger_memory_barrier();
   uint64_t val;
   while(1) {
     val = *v;
@@ -31,6 +32,7 @@ readfe(volatile uint64_t * v) {
 
 uint64_t
 writeef(volatile uint64_t * v, uint64_t new_val) {
+  stinger_memory_barrier();
   uint64_t val;
   while(1) {
     val = *v;
@@ -45,6 +47,7 @@ writeef(volatile uint64_t * v, uint64_t new_val) {
 
 uint64_t
 readff(volatile uint64_t * v) {
+  stinger_memory_barrier();
   uint64_t val = *v;
   while(val == MARKER) {
     val = *v;
@@ -54,6 +57,7 @@ readff(volatile uint64_t * v) {
 
 uint64_t
 writeff(volatile uint64_t * v, uint64_t new_val) {
+  stinger_memory_barrier();
   uint64_t val;
   while(1) {
     val = *v;
@@ -68,6 +72,8 @@ writeff(volatile uint64_t * v, uint64_t new_val) {
 
 uint64_t
 writexf(volatile uint64_t * v, uint64_t new_val) {
+  stinger_memory_barrier();
   *v = new_val;
+  stinger_memory_barrier();
   return new_val;
 }