/*

 * Copyright (c) 2016, 2019, Red Hat, Inc. All rights reserved.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

#ifndef SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP

#define SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP

#include "gc/shared/owstTaskTerminator.hpp"

#include "gc/shared/taskqueue.hpp"

#include "memory/allocation.hpp"

#include "runtime/mutex.hpp"

#include "runtime/thread.hpp"

template<class E, MEMFLAGS F, unsigned int N = TASKQUEUE_SIZE>

class BufferedOverflowTaskQueue: public OverflowTaskQueue<E, F, N>

{

public:

  typedef OverflowTaskQueue<E, F, N> taskqueue_t;

  BufferedOverflowTaskQueue() : _buf_empty(true) {};

  TASKQUEUE_STATS_ONLY(using taskqueue_t::stats;)

  // Push task t into the queue. Returns true on success.

  inline bool push(E t);

  // Attempt to pop from the queue. Returns true on success.

  inline bool pop(E &t);

  inline void clear();

  inline bool is_empty()        const {

    return _buf_empty && taskqueue_t::is_empty();

  }

private:

  bool _buf_empty;

  E _elem;

};

// ObjArrayChunkedTask

//

// Encodes both regular oops, and the array oops plus chunking data for parallel array processing.

// The design goal is to make the regular oop ops very fast, because that would be the prevailing

// case. On the other hand, it should not block parallel array processing from efficiently dividing

// the array work.

//

// The idea is to steal the bits from the 64-bit oop to encode array data, if needed. For the

// proper divide-and-conquer strategies, we want to encode the "blocking" data. It turns out, the

// most efficient way to do this is to encode the array block as (chunk * 2^pow), where it is assumed

// that the block has the size of 2^pow. This requires for pow to have only 5 bits (2^32) to encode

// all possible arrays.

//

//    |---------oop---------|-pow-|--chunk---|

//    0                    49     54        64

//

// By definition, chunk == 0 means "no chunk", i.e. chunking starts from 1.

//

// This encoding gives a few interesting benefits:

//

// a) Encoding/decoding regular oops is very simple, because the upper bits are zero in that task:

//

//    |---------oop---------|00000|0000000000| // no chunk data

//

//    This helps the most ubiquitous path. The initialization amounts to putting the oop into the word

//    with zero padding. Testing for "chunkedness" is testing for zero with chunk mask.

//

// b) Splitting tasks for divide-and-conquer is possible. Suppose we have chunk <C, P> that covers

// interval [ (C-1)*2^P; C*2^P ). We can then split it into two chunks:

//      <2*C - 1, P-1>, that covers interval [ (2*C - 2)*2^(P-1); (2*C - 1)*2^(P-1) )

//      <2*C, P-1>,     that covers interval [ (2*C - 1)*2^(P-1);       2*C*2^(P-1) )

//

//    Observe that the union of these two intervals is:

//      [ (2*C - 2)*2^(P-1); 2*C*2^(P-1) )

//

//    ...which is the original interval:

//      [ (C-1)*2^P; C*2^P )

//

// c) The divide-and-conquer strategy could even start with chunk <1, round-log2-len(arr)>, and split

//    down in the parallel threads, which alleviates the upfront (serial) splitting costs.

//

// Encoding limitations caused by current bitscales mean:

//    10 bits for chunk: max 1024 blocks per array

//     5 bits for power: max 2^32 array

//    49 bits for   oop: max 512 TB of addressable space

//

// Stealing bits from oop trims down the addressable space. Stealing too few bits for chunk ID limits

// potential parallelism. Stealing too few bits for pow limits the maximum array size that can be handled.

// In future, these might be rebalanced to favor one degree of freedom against another. For example,

// if/when Arrays 2.0 bring 2^64-sized arrays, we might need to steal another bit for power. We could regain

// some bits back if chunks are counted in ObjArrayMarkingStride units.

//

// There is also a fallback version that uses plain fields, when we don't have enough space to steal the

// bits from the native pointer. It is useful to debug the optimized version.

//

#ifdef _MSC_VER

#pragma warning(push)

// warning C4522: multiple assignment operators specified

#pragma warning( disable:4522 )

#endif

#ifdef _LP64

#define SHENANDOAH_OPTIMIZED_OBJTASK 1

#else

#define SHENANDOAH_OPTIMIZED_OBJTASK 0

#endif

#if SHENANDOAH_OPTIMIZED_OBJTASK

class ObjArrayChunkedTask

{

public:

  enum {

    chunk_bits   = 10,

    pow_bits     = 5,

    oop_bits     = sizeof(uintptr_t)*8 - chunk_bits - pow_bits

  };

  enum {

    oop_shift    = 0,

    pow_shift    = oop_shift + oop_bits,

    chunk_shift  = pow_shift + pow_bits

  };

public:

  ObjArrayChunkedTask(oop o = NULL) {

    assert(decode_oop(encode_oop(o)) ==  o, "oop can be encoded: " PTR_FORMAT, p2i(o));

    _obj = encode_oop(o);

  }

  ObjArrayChunkedTask(oop o, int chunk, int pow) {

    assert(decode_oop(encode_oop(o)) == o, "oop can be encoded: " PTR_FORMAT, p2i(o));

    assert(decode_chunk(encode_chunk(chunk)) == chunk, "chunk can be encoded: %d", chunk);

    assert(decode_pow(encode_pow(pow)) == pow, "pow can be encoded: %d", pow);

    _obj = encode_oop(o) | encode_chunk(chunk) | encode_pow(pow);

  }

  ObjArrayChunkedTask(const ObjArrayChunkedTask& t): _obj(t._obj) { }

  ObjArrayChunkedTask& operator =(const ObjArrayChunkedTask& t) {

    _obj = t._obj;

    return *this;

  }

  volatile ObjArrayChunkedTask&

  operator =(const volatile ObjArrayChunkedTask& t) volatile {

    (void)const_cast<uintptr_t&>(_obj = t._obj);

    return *this;

  }

  inline oop decode_oop(uintptr_t val) const {

    return (oop) reinterpret_cast<void*>((val >> oop_shift) & right_n_bits(oop_bits));

  }

  inline int decode_chunk(uintptr_t val) const {

    return (int) ((val >> chunk_shift) & right_n_bits(chunk_bits));

  }

  inline int decode_pow(uintptr_t val) const {

    return (int) ((val >> pow_shift) & right_n_bits(pow_bits));

  }

  inline uintptr_t encode_oop(oop obj) const {

    return ((uintptr_t)(void*) obj) << oop_shift;

  }

  inline uintptr_t encode_chunk(int chunk) const {

    return ((uintptr_t) chunk) << chunk_shift;

  }

  inline uintptr_t encode_pow(int pow) const {

    return ((uintptr_t) pow) << pow_shift;

  }

  inline oop obj()   const { return decode_oop(_obj);   }

  inline int chunk() const { return decode_chunk(_obj); }

  inline int pow()   const { return decode_pow(_obj);   }

  inline bool is_not_chunked() const { return (_obj & ~right_n_bits(oop_bits + pow_bits)) == 0; }

  DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.

  static uintptr_t max_addressable() {

    return nth_bit(oop_bits);

  }

  static int chunk_size() {

    return nth_bit(chunk_bits);

  }

private:

  uintptr_t _obj;

};

#else

class ObjArrayChunkedTask

{

public:

  enum {

    chunk_bits  = 10,

    pow_bits    = 5,

  };

public:

  ObjArrayChunkedTask(oop o = NULL, int chunk = 0, int pow = 0): _obj(o) {

    assert(0 <= chunk && chunk < nth_bit(chunk_bits), "chunk is sane: %d", chunk);

    assert(0 <= pow && pow < nth_bit(pow_bits), "pow is sane: %d", pow);

    _chunk = chunk;

    _pow = pow;

  }

  ObjArrayChunkedTask(const ObjArrayChunkedTask& t): _obj(t._obj), _chunk(t._chunk), _pow(t._pow) { }

  ObjArrayChunkedTask& operator =(const ObjArrayChunkedTask& t) {

    _obj = t._obj;

    _chunk = t._chunk;

    _pow = t._pow;

    return *this;

  }

  volatile ObjArrayChunkedTask&

  operator =(const volatile ObjArrayChunkedTask& t) volatile {

    (void)const_cast<oop&>(_obj = t._obj);

    _chunk = t._chunk;

    _pow = t._pow;

    return *this;

  }

  inline oop obj()   const { return _obj; }

  inline int chunk() const { return _chunk; }

  inline int pow()  const { return _pow; }

  inline bool is_not_chunked() const { return _chunk == 0; }

  DEBUG_ONLY(bool is_valid() const); // Tasks to be pushed/popped must be valid.

  static size_t max_addressable() {

    return sizeof(oop);

  }

  static int chunk_size() {

    return nth_bit(chunk_bits);

  }

private:

  oop _obj;

  int _chunk;

  int _pow;

};

#endif // SHENANDOAH_OPTIMIZED_OBJTASK

#ifdef _MSC_VER

#pragma warning(pop)

#endif

typedef ObjArrayChunkedTask ShenandoahMarkTask;

typedef BufferedOverflowTaskQueue<ShenandoahMarkTask, mtGC> ShenandoahBufferedOverflowTaskQueue;

typedef Padded<ShenandoahBufferedOverflowTaskQueue> ShenandoahObjToScanQueue;

template <class T, MEMFLAGS F>

class ParallelClaimableQueueSet: public GenericTaskQueueSet<T, F> {

private:

  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile jint));

  volatile jint     _claimed_index;

  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);

  debug_only(uint   _reserved;  )

public:

  using GenericTaskQueueSet<T, F>::size;

public:

  ParallelClaimableQueueSet(int n) : GenericTaskQueueSet<T, F>(n), _claimed_index(0) {

    debug_only(_reserved = 0; )

  }

  void clear_claimed() { _claimed_index = 0; }

  T*   claim_next();

  // reserve queues that not for parallel claiming

  void reserve(uint n) {

    assert(n <= size(), "Sanity");

    _claimed_index = (jint)n;

    debug_only(_reserved = n;)

  }

  debug_only(uint get_reserved() const { return (uint)_reserved; })

};

template <class T, MEMFLAGS F>

T* ParallelClaimableQueueSet<T, F>::claim_next() {

  jint size = (jint)GenericTaskQueueSet<T, F>::size();

  if (_claimed_index >= size) {

    return NULL;

  }

  if (index <= size) {

    return GenericTaskQueueSet<T, F>::queue((uint)index - 1);

  } else {

    return NULL;

  }

}

class ShenandoahObjToScanQueueSet: public ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC> {

public:

  ShenandoahObjToScanQueueSet(int n) : ParallelClaimableQueueSet<ShenandoahObjToScanQueue, mtGC>(n) {}

  bool is_empty();

  void clear();

#if TASKQUEUE_STATS

  static void print_taskqueue_stats_hdr(outputStream* const st);

  void print_taskqueue_stats() const;

  void reset_taskqueue_stats();

#endif // TASKQUEUE_STATS

};

class ShenandoahTerminatorTerminator : public TerminatorTerminator {

private:

  ShenandoahHeap* _heap;

public:

  ShenandoahTerminatorTerminator(ShenandoahHeap* const heap) : _heap(heap) { }

  // return true, terminates immediately, even if there's remaining work left

  virtual bool should_exit_termination() { return _heap->cancelled_gc(); }

};

class ShenandoahTaskTerminator : public StackObj {

private:

  OWSTTaskTerminator* const   _terminator;

public:

  ShenandoahTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set);

  ~ShenandoahTaskTerminator();

  bool offer_termination(ShenandoahTerminatorTerminator* terminator) {

    return _terminator->offer_termination(terminator);

  }

  void reset_for_reuse() { _terminator->reset_for_reuse(); }

  bool offer_termination() { return offer_termination((ShenandoahTerminatorTerminator*)NULL); }

};

#endif // SHARE_GC_SHENANDOAH_SHENANDOAHTASKQUEUE_HPP