1 /* ---------------------------------------------------------------------------
3 * (c) The GHC Team, 2000-2008
5 * Sparking support for PARALLEL_HASKELL and THREADED_RTS versions of the RTS.
7 -------------------------------------------------------------------------*/
9 #include "PosixSource.h"
18 #if defined(THREADED_RTS)
21 initSparkPools( void )
23 /* walk over the capabilities, allocating a spark pool for each one */
25 for (i = 0; i < n_capabilities; i++) {
26 capabilities[i].sparks = newWSDeque(RtsFlags.ParFlags.maxLocalSparks);
31 freeSparkPool (SparkPool *pool)
36 /* -----------------------------------------------------------------------------
38 * Turn a spark into a real thread
40 * -------------------------------------------------------------------------- */
43 createSparkThread (Capability *cap)
47 tso = createIOThread (cap, RtsFlags.GcFlags.initialStkSize,
48 (StgClosure *)runSparks_closure);
50 traceEventCreateSparkThread(cap, tso->id);
52 appendToRunQueue(cap,tso);
55 /* --------------------------------------------------------------------------
56 * newSpark: create a new spark, as a result of calling "par"
57 * Called directly from STG.
58 * -------------------------------------------------------------------------- */
61 newSpark (StgRegTable *reg, StgClosure *p)
63 Capability *cap = regTableToCapability(reg);
64 SparkPool *pool = cap->sparks;
66 /* I am not sure whether this is the right thing to do.
67 * Maybe it is better to exploit the tag information
68 * instead of throwing it away?
72 if (closure_SHOULD_SPARK(p)) {
76 cap->sparks_created++;
81 /* -----------------------------------------------------------------------------
83 * tryStealSpark: try to steal a spark from a Capability.
85 * Returns a valid spark, or NULL if the pool was empty, and can
86 * occasionally return NULL if there was a race with another thread
87 * stealing from the same pool. In this case, try again later.
89 -------------------------------------------------------------------------- */
92 tryStealSpark (Capability *cap)
94 SparkPool *pool = cap->sparks;
98 stolen = stealWSDeque_(pool);
99 // use the no-loopy version, stealWSDeque_(), since if we get a
100 // spurious NULL here the caller may want to try stealing from
101 // other pools before trying again.
102 } while (stolen != NULL && !closure_SHOULD_SPARK(stolen));
107 /* --------------------------------------------------------------------------
108 * Remove all sparks from the spark queues which should not spark any
109 * more. Called after GC. We assume exclusive access to the structure
110 * and replace all sparks in the queue, see explanation below. At exit,
111 * the spark pool only contains sparkable closures.
112 * -------------------------------------------------------------------------- */
115 pruneSparkQueue (Capability *cap)
118 StgClosurePtr spark, tmp, *elements;
119 nat n, pruned_sparks; // stats only
120 StgWord botInd,oldBotInd,currInd; // indices in array (always < size)
121 const StgInfoTable *info;
128 // it is possible that top > bottom, indicating an empty pool. We
129 // fix that here; this is only necessary because the loop below
131 if (pool->top > pool->bottom)
132 pool->top = pool->bottom;
134 // Take this opportunity to reset top/bottom modulo the size of
135 // the array, to avoid overflow. This is only possible because no
136 // stealing is happening during GC.
137 pool->bottom -= pool->top & ~pool->moduloSize;
138 pool->top &= pool->moduloSize;
139 pool->topBound = pool->top;
141 debugTrace(DEBUG_sparks,
142 "markSparkQueue: current spark queue len=%ld; (hd=%ld; tl=%ld)",
143 sparkPoolSize(pool), pool->bottom, pool->top);
145 ASSERT_WSDEQUE_INVARIANTS(pool);
147 elements = (StgClosurePtr *)pool->elements;
149 /* We have exclusive access to the structure here, so we can reset
150 bottom and top counters, and prune invalid sparks. Contents are
151 copied in-place if they are valuable, otherwise discarded. The
152 routine uses "real" indices t and b, starts by computing them
153 as the modulus size of top and bottom,
157 At the beginning, the pool structure can look like this:
158 ( bottom % size >= top % size , no wrap-around)
160 ___________***********_________________
162 or like this ( bottom % size < top % size, wrap-around )
164 ***********__________******************
165 As we need to remove useless sparks anyway, we make one pass
166 between t and b, moving valuable content to b and subsequent
167 cells (wrapping around when the size is reached).
170 ***********OOO_______XX_X__X?**********
173 After this movement, botInd becomes the new bottom, and old
174 bottom becomes the new top index, both as indices in the array
178 currInd = (pool->top) & (pool->moduloSize); // mod
180 // copies of evacuated closures go to space from botInd on
181 // we keep oldBotInd to know when to stop
182 oldBotInd = botInd = (pool->bottom) & (pool->moduloSize); // mod
184 // on entry to loop, we are within the bounds
185 ASSERT( currInd < pool->size && botInd < pool->size );
187 while (currInd != oldBotInd ) {
188 /* must use != here, wrap-around at size
189 subtle: loop not entered if queue empty
192 /* check element at currInd. if valuable, evacuate and move to
193 botInd, otherwise move on */
194 spark = elements[currInd];
196 // We have to be careful here: in the parallel GC, another
197 // thread might evacuate this closure while we're looking at it,
198 // so grab the info pointer just once.
199 info = spark->header.info;
200 if (IS_FORWARDING_PTR(info)) {
201 tmp = (StgClosure*)UN_FORWARDING_PTR(info);
202 /* if valuable work: shift inside the pool */
203 if (closure_SHOULD_SPARK(tmp)) {
204 elements[botInd] = tmp; // keep entry (new address)
208 pruned_sparks++; // discard spark
209 cap->sparks_pruned++;
211 } else if (HEAP_ALLOCED(spark) &&
212 (Bdescr((P_)spark)->flags & BF_EVACUATED)) {
213 if (closure_SHOULD_SPARK(spark)) {
214 elements[botInd] = spark; // keep entry (new address)
218 pruned_sparks++; // discard spark
219 cap->sparks_pruned++;
222 pruned_sparks++; // discard spark
223 cap->sparks_pruned++;
228 // in the loop, we may reach the bounds, and instantly wrap around
229 ASSERT( currInd <= pool->size && botInd <= pool->size );
230 if ( currInd == pool->size ) { currInd = 0; }
231 if ( botInd == pool->size ) { botInd = 0; }
233 } // while-loop over spark pool elements
235 ASSERT(currInd == oldBotInd);
237 pool->top = oldBotInd; // where we started writing
238 pool->topBound = pool->top;
240 pool->bottom = (oldBotInd <= botInd) ? botInd : (botInd + pool->size);
241 // first free place we did not use (corrected by wraparound)
243 debugTrace(DEBUG_sparks, "pruned %d sparks", pruned_sparks);
245 debugTrace(DEBUG_sparks,
246 "new spark queue len=%ld; (hd=%ld; tl=%ld)",
247 sparkPoolSize(pool), pool->bottom, pool->top);
249 ASSERT_WSDEQUE_INVARIANTS(pool);
252 /* GC for the spark pool, called inside Capability.c for all
253 capabilities in turn. Blindly "evac"s complete spark pool. */
255 traverseSparkQueue (evac_fn evac, void *user, Capability *cap)
259 StgWord top,bottom, modMask;
263 ASSERT_WSDEQUE_INVARIANTS(pool);
266 bottom = pool->bottom;
267 sparkp = (StgClosurePtr*)pool->elements;
268 modMask = pool->moduloSize;
270 while (top < bottom) {
271 /* call evac for all closures in range (wrap-around via modulo)
272 * In GHC-6.10, evac takes an additional 1st argument to hold a
273 * GC-specific register, see rts/sm/GC.c::mark_root()
275 evac( user , sparkp + (top & modMask) );
279 debugTrace(DEBUG_sparks,
280 "traversed spark queue, len=%ld; (hd=%ld; tl=%ld)",
281 sparkPoolSize(pool), pool->bottom, pool->top);
284 /* ----------------------------------------------------------------------------
285 * balanceSparkPoolsCaps: takes an array of capabilities (usually: all
286 * capabilities) and its size. Accesses all spark pools and equally
287 * distributes the sparks among them.
289 * Could be called after GC, before Cap. release, from scheduler.
290 * -------------------------------------------------------------------------- */
291 void balanceSparkPoolsCaps(nat n_caps, Capability caps[])
292 GNUC3_ATTRIBUTE(__noreturn__);
294 void balanceSparkPoolsCaps(nat n_caps STG_UNUSED,
295 Capability caps[] STG_UNUSED) {
296 barf("not implemented");
302 newSpark (StgRegTable *reg STG_UNUSED, StgClosure *p STG_UNUSED)
308 #endif /* THREADED_RTS */