1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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  24 
  25 #ifndef SHARE_GC_SHARED_TASKQUEUE_INLINE_HPP
  26 #define SHARE_GC_SHARED_TASKQUEUE_INLINE_HPP
  27 
  28 #include "gc/shared/taskqueue.hpp"
  29 #include "memory/allocation.inline.hpp"
  30 #include "oops/oop.inline.hpp"
  31 #include "runtime/atomic.hpp"
  32 #include "runtime/orderAccess.hpp"
  33 #include "utilities/debug.hpp"
  34 #include "utilities/stack.inline.hpp"
  35 
  36 template <class T, MEMFLAGS F>
  37 inline GenericTaskQueueSet<T, F>::GenericTaskQueueSet(uint n) : _n(n) {
  38   typedef T* GenericTaskQueuePtr;
  39   _queues = NEW_C_HEAP_ARRAY(GenericTaskQueuePtr, n, F);
  40   for (uint i = 0; i < n; i++) {
  41     _queues[i] = NULL;
  42   }
  43 }
  44 
  45 template <class T, MEMFLAGS F>
  46 inline GenericTaskQueueSet<T, F>::~GenericTaskQueueSet() {
  47   FREE_C_HEAP_ARRAY(T*, _queues);
  48 }
  49 
  50 template<class E, MEMFLAGS F, unsigned int N>
  51 inline void GenericTaskQueue<E, F, N>::initialize() {
  52   _elems = ArrayAllocator<E>::allocate(N, F);
  53 }
  54 
  55 template<class E, MEMFLAGS F, unsigned int N>
  56 inline GenericTaskQueue<E, F, N>::~GenericTaskQueue() {
  57   ArrayAllocator<E>::free(const_cast<E*>(_elems), N);
  58 }
  59 
  60 template<class E, MEMFLAGS F, unsigned int N>
  61 bool GenericTaskQueue<E, F, N>::push_slow(E t, uint dirty_n_elems) {
  62   if (dirty_n_elems == N - 1) {
  63     // Actually means 0, so do the push.
  64     uint localBot = _bottom;
  65     // g++ complains if the volatile result of the assignment is
  66     // unused, so we cast the volatile away.  We cannot cast directly
  67     // to void, because gcc treats that as not using the result of the
  68     // assignment.  However, casting to E& means that we trigger an
  69     // unused-value warning.  So, we cast the E& to void.
  70     (void)const_cast<E&>(_elems[localBot] = t);
  71     Atomic::release_store(&_bottom, increment_index(localBot));
  72     TASKQUEUE_STATS_ONLY(stats.record_push());
  73     return true;
  74   }
  75   return false;
  76 }
  77 
  78 template<class E, MEMFLAGS F, unsigned int N> inline bool
  79 GenericTaskQueue<E, F, N>::push(E t) {
  80   uint localBot = _bottom;
  81   assert(localBot < N, "_bottom out of range.");
  82   idx_t top = _age.top();
  83   uint dirty_n_elems = dirty_size(localBot, top);
  84   assert(dirty_n_elems < N, "n_elems out of range.");
  85   if (dirty_n_elems < max_elems()) {
  86     // g++ complains if the volatile result of the assignment is
  87     // unused, so we cast the volatile away.  We cannot cast directly
  88     // to void, because gcc treats that as not using the result of the
  89     // assignment.  However, casting to E& means that we trigger an
  90     // unused-value warning.  So, we cast the E& to void.
  91     (void) const_cast<E&>(_elems[localBot] = t);
  92     Atomic::release_store(&_bottom, increment_index(localBot));
  93     TASKQUEUE_STATS_ONLY(stats.record_push());
  94     return true;
  95   } else {
  96     return push_slow(t, dirty_n_elems);
  97   }
  98 }
  99 
 100 template <class E, MEMFLAGS F, unsigned int N>
 101 inline bool OverflowTaskQueue<E, F, N>::push(E t)
 102 {
 103   if (!taskqueue_t::push(t)) {
 104     overflow_stack()->push(t);
 105     TASKQUEUE_STATS_ONLY(stats.record_overflow(overflow_stack()->size()));
 106   }
 107   return true;
 108 }
 109 
 110 template <class E, MEMFLAGS F, unsigned int N>
 111 inline bool OverflowTaskQueue<E, F, N>::try_push_to_taskqueue(E t) {
 112   return taskqueue_t::push(t);
 113 }
 114 
 115 // pop_local_slow() is done by the owning thread and is trying to
 116 // get the last task in the queue.  It will compete with pop_global()
 117 // that will be used by other threads.  The tag age is incremented
 118 // whenever the queue goes empty which it will do here if this thread
 119 // gets the last task or in pop_global() if the queue wraps (top == 0
 120 // and pop_global() succeeds, see pop_global()).
 121 template<class E, MEMFLAGS F, unsigned int N>
 122 bool GenericTaskQueue<E, F, N>::pop_local_slow(uint localBot, Age oldAge) {
 123   // This queue was observed to contain exactly one element; either this
 124   // thread will claim it, or a competing "pop_global".  In either case,
 125   // the queue will be logically empty afterwards.  Create a new Age value
 126   // that represents the empty queue for the given value of "_bottom".  (We
 127   // must also increment "tag" because of the case where "bottom == 1",
 128   // "top == 0".  A pop_global could read the queue element in that case,
 129   // then have the owner thread do a pop followed by another push.  Without
 130   // the incrementing of "tag", the pop_global's CAS could succeed,
 131   // allowing it to believe it has claimed the stale element.)
 132   Age newAge((idx_t)localBot, oldAge.tag() + 1);
 133   // Perhaps a competing pop_global has already incremented "top", in which
 134   // case it wins the element.
 135   if (localBot == oldAge.top()) {
 136     // No competing pop_global has yet incremented "top"; we'll try to
 137     // install new_age, thus claiming the element.
 138     Age tempAge = _age.cmpxchg(newAge, oldAge);
 139     if (tempAge == oldAge) {
 140       // We win.
 141       assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
 142       TASKQUEUE_STATS_ONLY(stats.record_pop_slow());
 143       return true;
 144     }
 145   }
 146   // We lose; a completing pop_global gets the element.  But the queue is empty
 147   // and top is greater than bottom.  Fix this representation of the empty queue
 148   // to become the canonical one.
 149   _age.set(newAge);
 150   assert(dirty_size(localBot, _age.top()) != N - 1, "sanity");
 151   return false;
 152 }
 153 
 154 template<class E, MEMFLAGS F, unsigned int N> inline bool
 155 GenericTaskQueue<E, F, N>::pop_local(volatile E& t, uint threshold) {
 156   uint localBot = _bottom;
 157   // This value cannot be N-1.  That can only occur as a result of
 158   // the assignment to bottom in this method.  If it does, this method
 159   // resets the size to 0 before the next call (which is sequential,
 160   // since this is pop_local.)
 161   uint dirty_n_elems = dirty_size(localBot, _age.top());
 162   assert(dirty_n_elems != N - 1, "Shouldn't be possible...");
 163   if (dirty_n_elems <= threshold) return false;
 164   localBot = decrement_index(localBot);
 165   _bottom = localBot;
 166   // This is necessary to prevent any read below from being reordered
 167   // before the store just above.
 168   OrderAccess::fence();
 169   // g++ complains if the volatile result of the assignment is
 170   // unused, so we cast the volatile away.  We cannot cast directly
 171   // to void, because gcc treats that as not using the result of the
 172   // assignment.  However, casting to E& means that we trigger an
 173   // unused-value warning.  So, we cast the E& to void.
 174   (void) const_cast<E&>(t = _elems[localBot]);
 175   // This is a second read of "age"; the "size()" above is the first.
 176   // If there's still at least one element in the queue, based on the
 177   // "_bottom" and "age" we've read, then there can be no interference with
 178   // a "pop_global" operation, and we're done.
 179   idx_t tp = _age.top();    // XXX
 180   if (size(localBot, tp) > 0) {
 181     assert(dirty_size(localBot, tp) != N - 1, "sanity");
 182     TASKQUEUE_STATS_ONLY(stats.record_pop());
 183     return true;
 184   } else {
 185     // Otherwise, the queue contained exactly one element; we take the slow
 186     // path.
 187 
 188     // The barrier is required to prevent reordering the two reads of _age:
 189     // one is the _age.get() below, and the other is _age.top() above the if-stmt.
 190     // The algorithm may fail if _age.get() reads an older value than _age.top().
 191     OrderAccess::loadload();
 192     return pop_local_slow(localBot, _age.get());
 193   }
 194 }
 195 
 196 template <class E, MEMFLAGS F, unsigned int N>
 197 bool OverflowTaskQueue<E, F, N>::pop_overflow(E& t)
 198 {
 199   if (overflow_empty()) return false;
 200   t = overflow_stack()->pop();
 201   return true;
 202 }
 203 
 204 template<class E, MEMFLAGS F, unsigned int N>
 205 bool GenericTaskQueue<E, F, N>::pop_global(volatile E& t) {
 206   Age oldAge = _age.get();
 207   // Architectures with weak memory model require a barrier here
 208   // to guarantee that bottom is not older than age,
 209   // which is crucial for the correctness of the algorithm.
 210 #ifndef CPU_MULTI_COPY_ATOMIC
 211   OrderAccess::fence();
 212 #endif
 213   uint localBot = Atomic::load_acquire(&_bottom);
 214   uint n_elems = size(localBot, oldAge.top());
 215   if (n_elems == 0) {
 216     return false;
 217   }
 218 
 219   // g++ complains if the volatile result of the assignment is
 220   // unused, so we cast the volatile away.  We cannot cast directly
 221   // to void, because gcc treats that as not using the result of the
 222   // assignment.  However, casting to E& means that we trigger an
 223   // unused-value warning.  So, we cast the E& to void.
 224   (void) const_cast<E&>(t = _elems[oldAge.top()]);
 225   Age newAge(oldAge);
 226   newAge.increment();
 227   Age resAge = _age.cmpxchg(newAge, oldAge);
 228 
 229   // Note that using "_bottom" here might fail, since a pop_local might
 230   // have decremented it.
 231   assert(dirty_size(localBot, newAge.top()) != N - 1, "sanity");
 232   return resAge == oldAge;
 233 }
 234 
 235 inline int randomParkAndMiller(int *seed0) {
 236   const int a =      16807;
 237   const int m = 2147483647;
 238   const int q =     127773;  /* m div a */
 239   const int r =       2836;  /* m mod a */
 240   STATIC_ASSERT(sizeof(int) == 4);
 241   int seed = *seed0;
 242   int hi   = seed / q;
 243   int lo   = seed % q;
 244   int test = a * lo - r * hi;
 245   if (test > 0) {
 246     seed = test;
 247   } else {
 248     seed = test + m;
 249   }
 250   *seed0 = seed;
 251   return seed;
 252 }
 253 
 254 template<class E, MEMFLAGS F, unsigned int N>
 255 int GenericTaskQueue<E, F, N>::next_random_queue_id() {
 256   return randomParkAndMiller(&_seed);
 257 }
 258 
 259 template<class T, MEMFLAGS F> bool
 260 GenericTaskQueueSet<T, F>::steal_best_of_2(uint queue_num, E& t) {
 261   if (_n > 2) {
 262     T* const local_queue = _queues[queue_num];
 263     uint k1 = queue_num;
 264 
 265     if (local_queue->is_last_stolen_queue_id_valid()) {
 266       k1 = local_queue->last_stolen_queue_id();
 267       assert(k1 != queue_num, "Should not be the same");
 268     } else {
 269       while (k1 == queue_num) {
 270         k1 = local_queue->next_random_queue_id() % _n;
 271       }
 272     }
 273 
 274     uint k2 = queue_num;
 275     while (k2 == queue_num || k2 == k1) {
 276       k2 = local_queue->next_random_queue_id() % _n;
 277     }
 278     // Sample both and try the larger.
 279     uint sz1 = _queues[k1]->size();
 280     uint sz2 = _queues[k2]->size();
 281 
 282     uint sel_k = 0;
 283     bool suc = false;
 284 
 285     if (sz2 > sz1) {
 286       sel_k = k2;
 287       suc = _queues[k2]->pop_global(t);
 288     } else if (sz1 > 0) {
 289       sel_k = k1;
 290       suc = _queues[k1]->pop_global(t);
 291     }
 292 
 293     if (suc) {
 294       local_queue->set_last_stolen_queue_id(sel_k);
 295     } else {
 296       local_queue->invalidate_last_stolen_queue_id();
 297     }
 298 
 299     return suc;
 300   } else if (_n == 2) {
 301     // Just try the other one.
 302     uint k = (queue_num + 1) % 2;
 303     return _queues[k]->pop_global(t);
 304   } else {
 305     assert(_n == 1, "can't be zero.");
 306     return false;
 307   }
 308 }
 309 
 310 template<class T, MEMFLAGS F> bool
 311 GenericTaskQueueSet<T, F>::steal(uint queue_num, E& t) {
 312   for (uint i = 0; i < 2 * _n; i++) {
 313     TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal_attempt());
 314     if (steal_best_of_2(queue_num, t)) {
 315       TASKQUEUE_STATS_ONLY(queue(queue_num)->stats.record_steal());
 316       return true;
 317     }
 318   }
 319   return false;
 320 }
 321 
 322 template <unsigned int N, MEMFLAGS F>
 323 inline typename TaskQueueSuper<N, F>::Age TaskQueueSuper<N, F>::Age::cmpxchg(const Age new_age, const Age old_age) volatile {
 324   return Atomic::cmpxchg(new_age._data, &_data, old_age._data);
 325 }
 326 
 327 template<class E, MEMFLAGS F, unsigned int N>
 328 template<class Fn>
 329 inline void GenericTaskQueue<E, F, N>::iterate(Fn fn) {
 330   uint iters = size();
 331   uint index = _bottom;
 332   for (uint i = 0; i < iters; ++i) {
 333     index = decrement_index(index);
 334     fn(const_cast<E&>(_elems[index])); // cast away volatility
 335   }
 336 }
 337 
 338 
 339 #endif // SHARE_GC_SHARED_TASKQUEUE_INLINE_HPP
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