#include "WSDeque.h"
#include "SMP.h" // for cas
-#if defined(THREADED_RTS)
-
#define CASTOP(addr,old,new) ((old) == cas(((StgPtr)addr),(old),(new)))
/* -----------------------------------------------------------------------------
/* also a bit tricky, has to avoid concurrent steal() calls by
accessing top with cas, when there is only one element left */
StgWord t, b;
- void ** pos;
long currSize;
void * removed;
ASSERT_WSDEQUE_INVARIANTS(q);
b = q->bottom;
- /* "decrement b as a test, see what happens" */
- q->bottom = --b;
- pos = (q->elements) + (b & (q->moduloSize));
+
+ // "decrement b as a test, see what happens"
+ b--;
+ q->bottom = b;
+
+ // very important that the following read of q->top does not occur
+ // before the earlier write to q->bottom.
+ store_load_barrier();
+
t = q->top; /* using topBound would give an *upper* bound, we
need a lower bound. We use the real top here, but
can update the topBound value */
q->topBound = t;
- currSize = b - t;
+ currSize = (long)b - (long)t;
if (currSize < 0) { /* was empty before decrementing b, set b
consistently and abort */
q->bottom = t;
return NULL;
}
- removed = *pos;
+
+ // read the element at b
+ removed = q->elements[b & q->moduloSize];
+
if (currSize > 0) { /* no danger, still elements in buffer after b-- */
// debugBelch("popWSDeque: t=%ld b=%ld = %ld\n", t, b, removed);
return removed;
void *
stealWSDeque_ (WSDeque *q)
{
- void ** pos;
- void ** arraybase;
- StgWord sz;
void * stolen;
StgWord b,t;
// Can't do this on someone else's spark pool:
// ASSERT_WSDEQUE_INVARIANTS(q);
- b = q->bottom;
+ // NB. these loads must be ordered, otherwise there is a race
+ // between steal and pop.
t = q->top;
+ load_load_barrier();
+ b = q->bottom;
// NB. b and t are unsigned; we need a signed value for the test
// below, because it is possible that t > b during a
}
/* now access array, see pushBottom() */
- arraybase = q->elements;
- sz = q->moduloSize;
- pos = arraybase + (t & sz);
- stolen = *pos;
+ stolen = q->elements[t & q->moduloSize];
/* now decide whether we have won */
if ( !(CASTOP(&(q->top),t,t+1)) ) {
pushWSDeque (WSDeque* q, void * elem)
{
StgWord t;
- void ** pos;
+ StgWord b;
StgWord sz = q->moduloSize;
- StgWord b = q->bottom;
ASSERT_WSDEQUE_INVARIANTS(q);
q->topBound (accessed only by writer) instead.
This is why we do not just call empty(q) here.
*/
+ b = q->bottom;
t = q->topBound;
if ( (StgInt)b - (StgInt)t >= (StgInt)sz ) {
/* NB. 1. sz == q->size - 1, thus ">="
#endif
}
}
- pos = (q->elements) + (b & sz);
- *pos = elem;
- (q->bottom)++;
+
+ q->elements[b & sz] = elem;
+ q->bottom = b + 1;
ASSERT_WSDEQUE_INVARIANTS(q);
return rtsTrue;
}
-
-#endif