1 /*
   2  * Copyright (c) 2016, 2019, Red Hat, Inc. All rights reserved.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This code is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  11  * version 2 for more details (a copy is included in the LICENSE file that
  12  * accompanied this code).
  13  *
  14  * You should have received a copy of the GNU General Public License version
  15  * 2 along with this work; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  17  *
  18  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  19  * or visit www.oracle.com if you need additional information or have any
  20  * questions.
  21  *
  22  */
  23 
  24 #ifndef SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP
  25 #define SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP
  26 #include "gc/shared/owstTaskTerminator.hpp"
  27 #include "gc/shared/taskqueue.hpp"
  28 #include "memory/allocation.hpp"
  29 #include "runtime/mutex.hpp"
  30 #include "runtime/thread.hpp"
  31 
  32 template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>
  33 class BufferedOverflowTaskQueue: public OverflowTaskQueue<E, F, N>
  34 {
  35 public:
  36   typedef OverflowTaskQueue<E, F, N> taskqueue_t;
  37 
  38   BufferedOverflowTaskQueue() : _buf_empty(true) {};
  39 
  40   TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)
  41 
  42   // Push task t into the queue. Returns true on success.
  43   inline bool push(E t);
  44 
  45   // Attempt to pop from the queue. Returns true on success.
  46   inline bool pop(E &t);
  47 
  48   inline void clear();
  49 
  50   inline bool is_empty()        const {
  51     return _buf_empty && taskqueue_t::is_empty();
  52   }
  53 
  54 private:
  55   bool _buf_empty;
  56   E _elem;
  57 };
  58 
  59 // ObjArrayChunkedTask
  60 //
  61 // Encodes both regular oops, and the array oops plus chunking data for parallel array processing.
  62 // The design goal is to make the regular oop ops very fast, because that would be the prevailing
  63 // case. On the other hand, it should not block parallel array processing from efficiently dividing
  64 // the array work.
  65 //
  66 // The idea is to steal the bits from the 64-bit oop to encode array data, if needed. For the
  67 // proper divide-and-conquer strategies, we want to encode the "blocking" data. It turns out, the
  68 // most efficient way to do this is to encode the array block as (chunk * 2^pow), where it is assumed
  69 // that the block has the size of 2^pow. This requires for pow to have only 5 bits (2^32) to encode
  70 // all possible arrays.
  71 //
  72 //    |---------oop---------|-pow-|--chunk---|
  73 //    0                    49     54        64
  74 //
  75 // By definition, chunk == 0 means "no chunk", i.e. chunking starts from 1.
  76 //
  77 // This encoding gives a few interesting benefits:
  78 //
  79 // a) Encoding/decoding regular oops is very simple, because the upper bits are zero in that task:
  80 //
  81 //    |---------oop---------|00000|0000000000| // no chunk data
  82 //
  83 //    This helps the most ubiquitous path. The initialization amounts to putting the oop into the word
  84 //    with zero padding. Testing for "chunkedness" is testing for zero with chunk mask.
  85 //
  86 // b) Splitting tasks for divide-and-conquer is possible. Suppose we have chunk <C, P> that covers
  87 // interval [ (C-1)*2^P; C*2^P ). We can then split it into two chunks:
  88 //      <2*C - 1, P-1>, that covers interval [ (2*C - 2)*2^(P-1); (2*C - 1)*2^(P-1) )
  89 //      <2*C, P-1>,     that covers interval [ (2*C - 1)*2^(P-1);       2*C*2^(P-1) )
  90 //
  91 //    Observe that the union of these two intervals is:
  92 //      [ (2*C - 2)*2^(P-1); 2*C*2^(P-1) )
  93 //
  94 //    ...which is the original interval:
  95 //      [ (C-1)*2^P; C*2^P )
  96 //
  97 // c) The divide-and-conquer strategy could even start with chunk <1, round-log2-len(arr)>, and split
  98 //    down in the parallel threads, which alleviates the upfront (serial) splitting costs.
  99 //
 100 // Encoding limitations caused by current bitscales mean:
 101 //    10 bits for chunk: max 1024 blocks per array
 102 //     5 bits for power: max 2^32 array
 103 //    49 bits for   oop: max 512 TB of addressable space
 104 //
 105 // Stealing bits from oop trims down the addressable space. Stealing too few bits for chunk ID limits
 106 // potential parallelism. Stealing too few bits for pow limits the maximum array size that can be handled.
 107 // In future, these might be rebalanced to favor one degree of freedom against another. For example,
 108 // if/when Arrays 2.0 bring 2^64-sized arrays, we might need to steal another bit for power. We could regain
 109 // some bits back if chunks are counted in ObjArrayMarkingStride units.
 110 //
 111 // There is also a fallback version that uses plain fields, when we don't have enough space to steal the
 112 // bits from the native pointer. It is useful to debug the optimized version.
 113 //
 114 
 115 #ifdef _MSC_VER
 116 #pragma warning(push)
 117 // warning C4522: multiple assignment operators specified
 118 #pragma warning( disable:4522 )
 119 #endif
 120 
 121 #ifdef _LP64
 122 #define SHENANDOAH_OPTIMIZED_OBJTASK 1
 123 #else
 124 #define SHENANDOAH_OPTIMIZED_OBJTASK 0
 125 #endif
 126 
 127 #if SHENANDOAH_OPTIMIZED_OBJTASK
 128 class ObjArrayChunkedTask
 129 {
 130 public:
 131   enum {
 132     chunk_bits   = 10,
 133     pow_bits     = 5,
 134     oop_bits     = sizeof(uintptr_t)*8 - chunk_bits - pow_bits
 135   };
 136   enum {
 137     oop_shift    = 0,
 138     pow_shift    = oop_shift + oop_bits,
 139     chunk_shift  = pow_shift + pow_bits
 140   };
 141 
 142 public:
 143   ObjArrayChunkedTask(oop o = NULL) {
 144     assert(decode_oop(encode_oop(o)) ==  o, "oop can be encoded: " PTR_FORMAT, p2i(o));
 145     _obj = encode_oop(o);
 146   }
 147   ObjArrayChunkedTask(oop o, int chunk, int pow) {
 148     assert(decode_oop(encode_oop(o)) == o, "oop can be encoded: " PTR_FORMAT, p2i(o));
 149     assert(decode_chunk(encode_chunk(chunk)) == chunk, "chunk can be encoded: %d", chunk);
 150     assert(decode_pow(encode_pow(pow)) == pow, "pow can be encoded: %d", pow);
 151     _obj = encode_oop(o) | encode_chunk(chunk) | encode_pow(pow);
 152   }
 153   ObjArrayChunkedTask(const ObjArrayChunkedTask& t): _obj(t._obj) { }
 154 
 155   ObjArrayChunkedTask& operator =(const ObjArrayChunkedTask& t) {
 156     _obj = t._obj;
 157     return *this;
 158   }
 159   volatile ObjArrayChunkedTask&
 160   operator =(const volatile ObjArrayChunkedTask& t) volatile {
 161     (void)const_cast<uintptr_t&>(_obj = t._obj);
 162     return *this;
 163   }
 164 
 165   inline oop decode_oop(uintptr_t val) const {
 166     return (oop) reinterpret_cast<void*>((val >> oop_shift) & right_n_bits(oop_bits));
 167   }
 168 
 169   inline int decode_chunk(uintptr_t val) const {
 170     return (int) ((val >> chunk_shift) & right_n_bits(chunk_bits));
 171   }
 172 
 173   inline int decode_pow(uintptr_t val) const {
 174     return (int) ((val >> pow_shift) & right_n_bits(pow_bits));
 175   }
 176 
 177   inline uintptr_t encode_oop(oop obj) const {
 178     return ((uintptr_t)(void*) obj) << oop_shift;
 179   }
 180 
 181   inline uintptr_t encode_chunk(int chunk) const {
 182     return ((uintptr_t) chunk) << chunk_shift;
 183   }
 184 
 185   inline uintptr_t encode_pow(int pow) const {
 186     return ((uintptr_t) pow) << pow_shift;
 187   }
 188 
 189   inline oop obj()   const { return decode_oop(_obj);   }
 190   inline int chunk() const { return decode_chunk(_obj); }
 191   inline int pow()   const { return decode_pow(_obj);   }
 192   inline bool is_not_chunked() const { return (_obj & ~right_n_bits(oop_bits + pow_bits)) == 0; }
 193 
 194   DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
 195 
 196   static uintptr_t max_addressable() {
 197     return nth_bit(oop_bits);
 198   }
 199 
 200   static int chunk_size() {
 201     return nth_bit(chunk_bits);
 202   }
 203 
 204 private:
 205   uintptr_t _obj;
 206 };
 207 #else
 208 class ObjArrayChunkedTask
 209 {
 210 public:
 211   enum {
 212     chunk_bits  = 10,
 213     pow_bits    = 5,
 214   };
 215 public:
 216   ObjArrayChunkedTask(oop o = NULL, int chunk = 0, int pow = 0): _obj(o) {
 217     assert(0 <= chunk && chunk < nth_bit(chunk_bits), "chunk is sane: %d", chunk);
 218     assert(0 <= pow && pow < nth_bit(pow_bits), "pow is sane: %d", pow);
 219     _chunk = chunk;
 220     _pow = pow;
 221   }
 222   ObjArrayChunkedTask(const ObjArrayChunkedTask& t): _obj(t._obj), _chunk(t._chunk), _pow(t._pow) { }
 223 
 224   ObjArrayChunkedTask& operator =(const ObjArrayChunkedTask& t) {
 225     _obj = t._obj;
 226     _chunk = t._chunk;
 227     _pow = t._pow;
 228     return *this;
 229   }
 230   volatile ObjArrayChunkedTask&
 231   operator =(const volatile ObjArrayChunkedTask& t) volatile {
 232     (void)const_cast<oop&>(_obj = t._obj);
 233     _chunk = t._chunk;
 234     _pow = t._pow;
 235     return *this;
 236   }
 237 
 238   inline oop obj()   const { return _obj; }
 239   inline int chunk() const { return _chunk; }
 240   inline int pow()  const { return _pow; }
 241 
 242   inline bool is_not_chunked() const { return _chunk == 0; }
 243 
 244   DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.
 245 
 246   static size_t max_addressable() {
 247     return sizeof(oop);
 248   }
 249 
 250   static int chunk_size() {
 251     return nth_bit(chunk_bits);
 252   }
 253 
 254 private:
 255   oop _obj;
 256   int _chunk;
 257   int _pow;
 258 };
 259 #endif // SHENANDOAH_OPTIMIZED_OBJTASK
 260 
 261 #ifdef _MSC_VER
 262 #pragma warning(pop)
 263 #endif
 264 
 265 typedef ObjArrayChunkedTask ShenandoahMarkTask;
 266 typedef BufferedOverflowTaskQueue<ShenandoahMarkTask, mtGC> ShenandoahBufferedOverflowTaskQueue;
 267 typedef Padded<ShenandoahBufferedOverflowTaskQueue> ShenandoahObjToScanQueue;
 268 
 269 template <class T, MEMFLAGS F>
 270 class ParallelClaimableQueueSet: public GenericTaskQueueSet<T, F> {
 271 private:
 272   DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile jint));
 273   volatile jint     _claimed_index;
 274   DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);
 275 
 276   debug_only(uint   _reserved;  )
 277 
 278 public:
 279   using GenericTaskQueueSet<T, F>::size;
 280 
 281 public:
 282   ParallelClaimableQueueSet(int n) : GenericTaskQueueSet<T, F>(n), _claimed_index(0) {
 283     debug_only(_reserved = 0; )
 284   }
 285 
 286   void clear_claimed() { _claimed_index = 0; }
 287   T*   claim_next();
 288 
 289   // reserve queues that not for parallel claiming
 290   void reserve(uint n) {
 291     assert(n <= size(), "Sanity");
 292     _claimed_index = (jint)n;
 293     debug_only(_reserved = n;)
 294   }
 295 
 296   debug_only(uint get_reserved() const { return (uint)_reserved; })
 297 };
 298 
 299 template <class T, MEMFLAGS F>
 300 T* ParallelClaimableQueueSet<T, F>::claim_next() {
 301   jint size = (jint)GenericTaskQueueSet<T, F>::size();
 302 
 303   if (_claimed_index >= size) {
 304     return NULL;
 305   }
 306 
 307   jint index = Atomic::add(&_claimed_index, 1);
 308 
 309   if (index <= size) {
 310     return GenericTaskQueueSet<T, F>::queue((uint)index - 1);
 311   } else {
 312     return NULL;
 313   }
 314 }
 315 
 316 class ShenandoahObjToScanQueueSet: public ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC> {
 317 public:
 318   ShenandoahObjToScanQueueSet(int n) : ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC>(n) {}
 319 
 320   bool is_empty();
 321   void clear();
 322 
 323 #if TASKQUEUE_STATS
 324   static void print_taskqueue_stats_hdr(outputStream* const st);
 325   void print_taskqueue_stats() const;
 326   void reset_taskqueue_stats();
 327 #endif // TASKQUEUE_STATS
 328 };
 329 
 330 class ShenandoahTerminatorTerminator : public TerminatorTerminator {
 331 private:
 332   ShenandoahHeap* _heap;
 333 public:
 334   ShenandoahTerminatorTerminator(ShenandoahHeap* const heap) : _heap(heap) { }
 335   // return true, terminates immediately, even if there's remaining work left
 336   virtual bool should_exit_termination() { return _heap->cancelled_gc(); }
 337 };
 338 
 339 class ShenandoahTaskTerminator : public StackObj {
 340 private:
 341   OWSTTaskTerminator* const   _terminator;
 342 public:
 343   ShenandoahTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set);
 344   ~ShenandoahTaskTerminator();
 345 
 346   bool offer_termination(ShenandoahTerminatorTerminator* terminator) {
 347     return _terminator->offer_termination(terminator);
 348   }
 349 
 350   void reset_for_reuse() { _terminator->reset_for_reuse(); }
 351   bool offer_termination() { return offer_termination((ShenandoahTerminatorTerminator*)NULL); }
 352 };
 353 
 354 #endif // SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP