Implement stack chunks and separate TSO/STACK objects
[ghc.git] / rts / Sparks.c
1 /* ---------------------------------------------------------------------------
2 *
3 * (c) The GHC Team, 2000-2008
4 *
5 * Sparking support for PARALLEL_HASKELL and THREADED_RTS versions of the RTS.
6 *
7 -------------------------------------------------------------------------*/
8
9 #include "PosixSource.h"
10 #include "Rts.h"
11
12 #include "Schedule.h"
13 #include "RtsUtils.h"
14 #include "Trace.h"
15 #include "Prelude.h"
16 #include "Sparks.h"
17
18 #if defined(THREADED_RTS)
19
20 void
21 initSparkPools( void )
22 {
23 /* walk over the capabilities, allocating a spark pool for each one */
24 nat i;
25 for (i = 0; i < n_capabilities; i++) {
26 capabilities[i].sparks = newWSDeque(RtsFlags.ParFlags.maxLocalSparks);
27 }
28 }
29
30 void
31 freeSparkPool (SparkPool *pool)
32 {
33 freeWSDeque(pool);
34 }
35
36 /* -----------------------------------------------------------------------------
37 *
38 * Turn a spark into a real thread
39 *
40 * -------------------------------------------------------------------------- */
41
42 void
43 createSparkThread (Capability *cap)
44 {
45 StgTSO *tso;
46
47 tso = createIOThread (cap, RtsFlags.GcFlags.initialStkSize,
48 (StgClosure *)runSparks_closure);
49
50 traceEventCreateSparkThread(cap, tso->id);
51
52 appendToRunQueue(cap,tso);
53 }
54
55 /* --------------------------------------------------------------------------
56 * newSpark: create a new spark, as a result of calling "par"
57 * Called directly from STG.
58 * -------------------------------------------------------------------------- */
59
60 StgInt
61 newSpark (StgRegTable *reg, StgClosure *p)
62 {
63 Capability *cap = regTableToCapability(reg);
64 SparkPool *pool = cap->sparks;
65
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?
69 */
70 p = UNTAG_CLOSURE(p);
71
72 if (closure_SHOULD_SPARK(p)) {
73 pushWSDeque(pool,p);
74 }
75
76 cap->sparks_created++;
77
78 return 1;
79 }
80
81 /* -----------------------------------------------------------------------------
82 *
83 * tryStealSpark: try to steal a spark from a Capability.
84 *
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.
88 *
89 -------------------------------------------------------------------------- */
90
91 StgClosure *
92 tryStealSpark (Capability *cap)
93 {
94 SparkPool *pool = cap->sparks;
95 StgClosure *stolen;
96
97 do {
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));
103
104 return stolen;
105 }
106
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 * -------------------------------------------------------------------------- */
113
114 void
115 pruneSparkQueue (Capability *cap)
116 {
117 SparkPool *pool;
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;
122
123 n = 0;
124 pruned_sparks = 0;
125
126 pool = cap->sparks;
127
128 // it is possible that top > bottom, indicating an empty pool. We
129 // fix that here; this is only necessary because the loop below
130 // assumes it.
131 if (pool->top > pool->bottom)
132 pool->top = pool->bottom;
133
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;
140
141 debugTrace(DEBUG_sparks,
142 "markSparkQueue: current spark queue len=%ld; (hd=%ld; tl=%ld)",
143 sparkPoolSize(pool), pool->bottom, pool->top);
144
145 ASSERT_WSDEQUE_INVARIANTS(pool);
146
147 elements = (StgClosurePtr *)pool->elements;
148
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,
154
155 Copying:
156
157 At the beginning, the pool structure can look like this:
158 ( bottom % size >= top % size , no wrap-around)
159 t b
160 ___________***********_________________
161
162 or like this ( bottom % size < top % size, wrap-around )
163 b t
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).
168
169 b t
170 ***********OOO_______XX_X__X?**********
171 ^____move?____/
172
173 After this movement, botInd becomes the new bottom, and old
174 bottom becomes the new top index, both as indices in the array
175 size range.
176 */
177 // starting here
178 currInd = (pool->top) & (pool->moduloSize); // mod
179
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
183
184 // on entry to loop, we are within the bounds
185 ASSERT( currInd < pool->size && botInd < pool->size );
186
187 while (currInd != oldBotInd ) {
188 /* must use != here, wrap-around at size
189 subtle: loop not entered if queue empty
190 */
191
192 /* check element at currInd. if valuable, evacuate and move to
193 botInd, otherwise move on */
194 spark = elements[currInd];
195
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)
205 botInd++;
206 n++;
207 } else {
208 pruned_sparks++; // discard spark
209 cap->sparks_pruned++;
210 }
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)
215 botInd++;
216 n++;
217 } else {
218 pruned_sparks++; // discard spark
219 cap->sparks_pruned++;
220 }
221 } else {
222 pruned_sparks++; // discard spark
223 cap->sparks_pruned++;
224 }
225
226 currInd++;
227
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; }
232
233 } // while-loop over spark pool elements
234
235 ASSERT(currInd == oldBotInd);
236
237 pool->top = oldBotInd; // where we started writing
238 pool->topBound = pool->top;
239
240 pool->bottom = (oldBotInd <= botInd) ? botInd : (botInd + pool->size);
241 // first free place we did not use (corrected by wraparound)
242
243 debugTrace(DEBUG_sparks, "pruned %d sparks", pruned_sparks);
244
245 debugTrace(DEBUG_sparks,
246 "new spark queue len=%ld; (hd=%ld; tl=%ld)",
247 sparkPoolSize(pool), pool->bottom, pool->top);
248
249 ASSERT_WSDEQUE_INVARIANTS(pool);
250 }
251
252 /* GC for the spark pool, called inside Capability.c for all
253 capabilities in turn. Blindly "evac"s complete spark pool. */
254 void
255 traverseSparkQueue (evac_fn evac, void *user, Capability *cap)
256 {
257 StgClosure **sparkp;
258 SparkPool *pool;
259 StgWord top,bottom, modMask;
260
261 pool = cap->sparks;
262
263 ASSERT_WSDEQUE_INVARIANTS(pool);
264
265 top = pool->top;
266 bottom = pool->bottom;
267 sparkp = (StgClosurePtr*)pool->elements;
268 modMask = pool->moduloSize;
269
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()
274 */
275 evac( user , sparkp + (top & modMask) );
276 top++;
277 }
278
279 debugTrace(DEBUG_sparks,
280 "traversed spark queue, len=%ld; (hd=%ld; tl=%ld)",
281 sparkPoolSize(pool), pool->bottom, pool->top);
282 }
283
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.
288 *
289 * Could be called after GC, before Cap. release, from scheduler.
290 * -------------------------------------------------------------------------- */
291 void balanceSparkPoolsCaps(nat n_caps, Capability caps[])
292 GNUC3_ATTRIBUTE(__noreturn__);
293
294 void balanceSparkPoolsCaps(nat n_caps STG_UNUSED,
295 Capability caps[] STG_UNUSED) {
296 barf("not implemented");
297 }
298
299 #else
300
301 StgInt
302 newSpark (StgRegTable *reg STG_UNUSED, StgClosure *p STG_UNUSED)
303 {
304 /* nothing */
305 return 1;
306 }
307
308 #endif /* THREADED_RTS */