X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=rts%2FSparks.c;h=9e4492ac1925c66b4fe942d8a6480671200d4aac;hb=51cae5224f2f2f5db8b3196d0f5118ba4246701a;hp=ac11172a9d958299166be02b01e45c351a2f40ac;hpb=cf9650f2a1690c04051c716124bb0350adc74ae7;p=ghc-hetmet.git

diff --git a/rts/Sparks.c b/rts/Sparks.c
index ac11172..9e4492a 100644
--- a/rts/Sparks.c
+++ b/rts/Sparks.c
@@ -44,6 +44,7 @@
 #include "RtsUtils.h"
 #include "ParTicky.h"
 #include "Trace.h"
+#include "Prelude.h"
 
 #include "SMP.h" // for cas
 
@@ -53,9 +54,9 @@
 
 /* internal helpers ... */
 
-StgWord roundUp2(StgWord val);
-
-StgWord roundUp2(StgWord val) {
+static StgWord
+roundUp2(StgWord val)
+{
   StgWord rounded = 1;
 
   /* StgWord is unsigned anyway, only catch 0 */
@@ -69,25 +70,6 @@ StgWord roundUp2(StgWord val) {
   return rounded;
 }
 
-INLINE_HEADER
-rtsBool casTop(StgPtr addr, StgWord old, StgWord new);
-
-#if !defined(THREADED_RTS)
-/* missing def. in non THREADED RTS, and makes no sense anyway... */
-StgWord cas(StgPtr addr,StgWord old,StgWord new);
-StgWord cas(StgPtr addr,StgWord old,StgWord new) { 
-  barf("cas: not implemented without multithreading");
-  old = new = *addr; /* to avoid gcc warnings */
-}
-#endif
-
-INLINE_HEADER
-rtsBool casTop(StgWord* addr, StgWord old, StgWord new) {
-  StgWord res = cas((StgPtr) addr, old, new);
-  return ((res == old));
-}
-
-/* or simply like this */
 #define CASTOP(addr,old,new) ((old) == cas(((StgPtr)addr),(old),(new)))
 
 /* -----------------------------------------------------------------------------
@@ -97,8 +79,9 @@ rtsBool casTop(StgWord* addr, StgWord old, StgWord new) {
  * -------------------------------------------------------------------------- */
 
 /* constructor */
-SparkPool* initPool(StgWord size) {
-
+static SparkPool*
+initPool(StgWord size)
+{
   StgWord realsize; 
   SparkPool *q;
 
@@ -136,14 +119,17 @@ initSparkPools( void )
 }
 
 void
-freeSparkPool(SparkPool *pool) {
+freeSparkPool (SparkPool *pool)
+{
   /* should not interfere with concurrent findSpark() calls! And
      nobody should use the pointer any more. We cross our fingers...*/
   stgFree(pool->elements);
   stgFree(pool);
 }
 
-/* reclaimSpark(cap): remove a spark from the write end of the queue.
+/* -----------------------------------------------------------------------------
+ * 
+ * reclaimSpark: remove a spark from the write end of the queue.
  * Returns the removed spark, and NULL if a race is lost or the pool
  * empty.
  *
@@ -151,9 +137,12 @@ freeSparkPool(SparkPool *pool) {
  * concurrently stealing threads by using cas to modify the top field.
  * This routine should NEVER be called by a task which does not own
  * the capability. Can this be checked here?
- */
-StgClosure* reclaimSpark(Capability *cap) {
-  SparkPool *deque = cap->sparks;
+ *
+ * -------------------------------------------------------------------------- */
+
+StgClosure *
+reclaimSpark (SparkPool *deque)
+{
   /* 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;
@@ -196,30 +185,32 @@ StgClosure* reclaimSpark(Capability *cap) {
 
 /* -----------------------------------------------------------------------------
  * 
- * findSpark: find a spark on the current Capability that we can fork
- * into a thread.
+ * tryStealSpark: try to steal a spark from a Capability.
  *
- * May be called by concurrent threads, which synchronise on top
- * variable. Returns a spark, or NULL if pool empty or race lost.
+ * Returns a valid spark, or NULL if the pool was empty, and can
+ * occasionally return NULL if there was a race with another thread
+ * stealing from the same pool.  In this case, try again later.
  *
  -------------------------------------------------------------------------- */
 
-StgClosurePtr steal(SparkPool *deque);
-
-/* steal an element from the read end. Synchronises multiple callers
-   by failing with NULL return. Returns NULL when deque is empty. */
-StgClosurePtr steal(SparkPool *deque) {
+static StgClosurePtr
+steal(SparkPool *deque)
+{
   StgClosurePtr* pos;
   StgClosurePtr* arraybase;
   StgWord sz;
   StgClosurePtr stolen;
   StgWord b,t; 
 
-  ASSERT_SPARK_POOL_INVARIANTS(deque); 
+// Can't do this on someone else's spark pool:
+// ASSERT_SPARK_POOL_INVARIANTS(deque); 
 
   b = deque->bottom;
   t = deque->top;
-  if (b - t <= 0 ) { 
+
+  // NB. b and t are unsigned; we need a signed value for the test
+  // below.
+  if ((long)b - (long)t <= 0 ) { 
     return NULL; /* already looks empty, abort */
   }
 
@@ -231,47 +222,46 @@ StgClosurePtr steal(SparkPool *deque) {
 
   /* now decide whether we have won */
   if ( !(CASTOP(&(deque->top),t,t+1)) ) {
-    /* lost the race, someon else has changed top in the meantime */
-    stolen = NULL;    
+      /* lost the race, someon else has changed top in the meantime */
+      return NULL;
   }  /* else: OK, top has been incremented by the cas call */
 
+// Can't do this on someone else's spark pool:
+// ASSERT_SPARK_POOL_INVARIANTS(deque); 
 
-  ASSERT_SPARK_POOL_INVARIANTS(deque); 
-  /* return NULL or stolen element */
+  /* return stolen element */
   return stolen;
 }
 
 StgClosure *
-findSpark (Capability *cap)
+tryStealSpark (Capability *cap)
 {
-  SparkPool *deque = (cap->sparks);
+  SparkPool *pool = cap->sparks;
   StgClosure *stolen;
 
-  ASSERT_SPARK_POOL_INVARIANTS(deque); 
-
   do { 
-    /* keep trying until good spark found or pool looks empty. 
-       TODO is this a good idea? */
-
-    stolen = steal(deque);
-    
-  } while ( ( !stolen /* nothing stolen*/
-	      || !closure_SHOULD_SPARK(stolen)) /* spark not OK */
-	    && !looksEmpty(deque)); /* run empty, give up */
+      stolen = steal(pool);
+  } while (stolen != NULL && !closure_SHOULD_SPARK(stolen));
 
-  /* return stolen element */
   return stolen;
 }
 
 
-/* "guesses" whether a deque is empty. Can return false negatives in
-   presence of concurrent steal() calls, and false positives in
-   presence of a concurrent pushBottom().*/
-rtsBool looksEmpty(SparkPool* deque) {
+/* -----------------------------------------------------------------------------
+ * 
+ * "guesses" whether a deque is empty. Can return false negatives in
+ *  presence of concurrent steal() calls, and false positives in
+ *  presence of a concurrent pushBottom().
+ *
+ * -------------------------------------------------------------------------- */
+
+rtsBool
+looksEmpty(SparkPool* deque)
+{
   StgWord t = deque->top;
   StgWord b = deque->bottom;
   /* try to prefer false negatives by reading top first */
-  return (b - t <= 0);
+  return ((long)b - (long)t <= 0);
   /* => array is *never* completely filled, always 1 place free! */
 }
 
@@ -282,11 +272,12 @@ rtsBool looksEmpty(SparkPool* deque) {
  * -------------------------------------------------------------------------- */
 
 void
-createSparkThread (Capability *cap, StgClosure *p)
+createSparkThread (Capability *cap)
 {
     StgTSO *tso;
 
-    tso = createGenThread (cap, RtsFlags.GcFlags.initialStkSize, p);
+    tso = createIOThread (cap, RtsFlags.GcFlags.initialStkSize, 
+                          &base_GHCziConc_runSparks_closure);
     appendToRunQueue(cap,tso);
 }
 
@@ -297,11 +288,12 @@ createSparkThread (Capability *cap, StgClosure *p)
  * -------------------------------------------------------------------------- */
 
 #define DISCARD_NEW
-void pushBottom(SparkPool* deque, StgClosurePtr elem);
 
 /* enqueue an element. Should always succeed by resizing the array
    (not implemented yet, silently fails in that case). */
-void pushBottom(SparkPool* deque, StgClosurePtr elem) {
+static void
+pushBottom (SparkPool* deque, StgClosurePtr elem)
+{
   StgWord t;
   StgClosurePtr* pos;
   StgWord sz = deque->moduloSize; 
@@ -314,7 +306,10 @@ void pushBottom(SparkPool* deque, StgClosurePtr elem) {
      This is why we do not just call empty(deque) here.
   */
   t = deque->topBound;
-  if ( b - t >= sz ) { /* nota bene: sz == deque->size - 1, thus ">=" */
+  if ( (StgInt)b - (StgInt)t >= (StgInt)sz ) { 
+    /* NB. 1. sz == deque->size - 1, thus ">="
+           2. signed comparison, it is possible that t > b
+    */
     /* could be full, check the real top value in this case */
     t = deque->top;
     deque->topBound = t;
@@ -349,12 +344,16 @@ void pushBottom(SparkPool* deque, StgClosurePtr elem) {
 }
 
 
-/* this is called as a direct C-call from Stg => we need to keep the
-   pool in a register (???) */
+/* --------------------------------------------------------------------------
+ * newSpark: create a new spark, as a result of calling "par"
+ * Called directly from STG.
+ * -------------------------------------------------------------------------- */
+
 StgInt
 newSpark (StgRegTable *reg, StgClosure *p)
 {
-    SparkPool *pool = (reg->rCurrentTSO->cap->sparks);
+    Capability *cap = regTableToCapability(reg);
+    SparkPool *pool = cap->sparks;
 
     /* I am not sure whether this is the right thing to do.
      * Maybe it is better to exploit the tag information
@@ -368,6 +367,8 @@ newSpark (StgRegTable *reg, StgClosure *p)
       pushBottom(pool,p);
     }	
 
+    cap->sparks_created++;
+
     ASSERT_SPARK_POOL_INVARIANTS(pool);
     return 1;
 }
@@ -381,13 +382,14 @@ newSpark (StgRegTable *reg, StgClosure *p)
  * the spark pool only contains sparkable closures.
  * -------------------------------------------------------------------------- */
 
-static void
-pruneSparkQueue (Capability *cap)
+void
+pruneSparkQueue (evac_fn evac, void *user, Capability *cap)
 { 
     SparkPool *pool;
-    StgClosurePtr spark, evacspark, *elements;
+    StgClosurePtr spark, tmp, *elements;
     nat n, pruned_sparks; // stats only
     StgWord botInd,oldBotInd,currInd; // indices in array (always < size)
+    const StgInfoTable *info;
     
     PAR_TICKY_MARK_SPARK_QUEUE_START();
     
@@ -396,6 +398,19 @@ pruneSparkQueue (Capability *cap)
     
     pool = cap->sparks;
     
+    // it is possible that top > bottom, indicating an empty pool.  We
+    // fix that here; this is only necessary because the loop below
+    // assumes it.
+    if (pool->top > pool->bottom)
+        pool->top = pool->bottom;
+
+    // Take this opportunity to reset top/bottom modulo the size of
+    // the array, to avoid overflow.  This is only possible because no
+    // stealing is happening during GC.
+    pool->bottom  -= pool->top & ~pool->moduloSize;
+    pool->top     &= pool->moduloSize;
+    pool->topBound = pool->top;
+
     debugTrace(DEBUG_sched,
                "markSparkQueue: current spark queue len=%d; (hd=%ld; tl=%ld)",
                sparkPoolSize(pool), pool->bottom, pool->top);
@@ -450,13 +465,31 @@ pruneSparkQueue (Capability *cap)
 	 botInd, otherwise move on */
       spark = elements[currInd];
 
-      /* if valuable work: shift inside the pool */
-      if ( closure_SHOULD_SPARK(spark) ) {
-	elements[botInd] = spark; // keep entry (new address)
-	botInd++;
-	n++;
-      } else { 
-	pruned_sparks++; // discard spark
+      // We have to be careful here: in the parallel GC, another
+      // thread might evacuate this closure while we're looking at it,
+      // so grab the info pointer just once.
+      info = spark->header.info;
+      if (IS_FORWARDING_PTR(info)) {
+          tmp = (StgClosure*)UN_FORWARDING_PTR(info);
+          /* if valuable work: shift inside the pool */
+          if (closure_SHOULD_SPARK(tmp)) {
+              elements[botInd] = tmp; // keep entry (new address)
+              botInd++;
+              n++;
+          } else {
+              pruned_sparks++; // discard spark
+              cap->sparks_pruned++;
+          }
+      } else {
+          if (!(closure_flags[INFO_PTR_TO_STRUCT(info)->type] & _NS)) {
+              elements[botInd] = spark; // keep entry (new address)
+              evac (user, &elements[botInd]);
+              botInd++;
+              n++;
+          } else {
+              pruned_sparks++; // discard spark
+              cap->sparks_pruned++;
+          }
       }
       currInd++;
 
@@ -486,15 +519,6 @@ pruneSparkQueue (Capability *cap)
     ASSERT_SPARK_POOL_INVARIANTS(pool);
 }
 
-void
-pruneSparkQueues (void)
-{
-    nat i;
-    for (i = 0; i < n_capabilities; i++) {
-        pruneSparkQueue(&capabilities[i]);
-    }
-}
-
 /* GC for the spark pool, called inside Capability.c for all
    capabilities in turn. Blindly "evac"s complete spark pool. */
 void
@@ -528,7 +552,6 @@ traverseSparkQueue (evac_fn evac, void *user, Capability *cap)
 }
 
 /* ----------------------------------------------------------------------------
-
  * balanceSparkPoolsCaps: takes an array of capabilities (usually: all
  * capabilities) and its size. Accesses all spark pools and equally
  * distributes the sparks among them.
@@ -537,7 +560,8 @@ traverseSparkQueue (evac_fn evac, void *user, Capability *cap)
  * -------------------------------------------------------------------------- */
 void balanceSparkPoolsCaps(nat n_caps, Capability caps[]);
 
-void balanceSparkPoolsCaps(nat n_caps, Capability caps[]) {
+void balanceSparkPoolsCaps(nat n_caps STG_UNUSED, 
+                           Capability caps[] STG_UNUSED) {
   barf("not implemented");
 }