/*

 * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * 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.

 *

 */

#include "precompiled.hpp"

#include "gc/shared/satbMarkQueue.hpp"

#include "gc/shared/collectedHeap.hpp"

#include "logging/log.hpp"

#include "memory/allocation.inline.hpp"

#include "oops/oop.inline.hpp"

#include "runtime/atomic.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/os.hpp"

#include "runtime/safepoint.hpp"

#include "runtime/thread.hpp"

#include "runtime/threadSMR.hpp"

#include "runtime/vmThread.hpp"

#include "utilities/globalCounter.inline.hpp"

SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset) :

  // SATB queues are only active during marking cycles. We create

  // them with their active field set to false. If a thread is

  // created during a cycle and its SATB queue needs to be activated

  // before the thread starts running, we'll need to set its active

  // field to true. This must be done in the collector-specific

  // BarrierSet thread attachment protocol.

  PtrQueue(qset, false /* active */)

{ }

void SATBMarkQueue::flush() {

  // Filter now to possibly save work later.  If filtering empties the

  // buffer then flush_impl can deallocate the buffer.

  filter();

  flush_impl();

}

// This method will first apply filtering to the buffer. If filtering

// retains a small enough collection in the buffer, we can continue to

// use the buffer as-is, instead of enqueueing and replacing it.

void SATBMarkQueue::handle_completed_buffer() {

  // This method should only be called if there is a non-NULL buffer

  // that is full.

  assert(index() == 0, "pre-condition");

  assert(_buf != NULL, "pre-condition");

  filter();

  size_t threshold = satb_qset()->buffer_enqueue_threshold();

  // Ensure we'll enqueue completely full buffers.

  assert(threshold > 0, "enqueue threshold = 0");

  // Ensure we won't enqueue empty buffers.

  assert(threshold <= capacity(),

         "enqueue threshold " SIZE_FORMAT " exceeds capacity " SIZE_FORMAT,

         threshold, capacity());

  if (index() < threshold) {

    // Buffer is sufficiently full; enqueue and allocate a new one.

    enqueue_completed_buffer();

  } // Else continue to accumulate in buffer.

}

void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {

  assert(SafepointSynchronize::is_at_safepoint(),

         "SATB queues must only be processed at safepoints");

  if (_buf != NULL) {

    cl->do_buffer(&_buf[index()], size());

    reset();

  }

}

#ifndef PRODUCT

// Helpful for debugging

static void print_satb_buffer(const char* name,

                              void** buf,

                              size_t index,

                              size_t capacity) {

  tty->print_cr("  SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT

                " capacity: " SIZE_FORMAT,

                name, p2i(buf), index, capacity);

}

void SATBMarkQueue::print(const char* name) {

  print_satb_buffer(name, _buf, index(), capacity());

}

#endif // PRODUCT

SATBMarkQueueSet::SATBMarkQueueSet(BufferNode::Allocator* allocator) :

  PtrQueueSet(allocator),

  _list(),

  _count_and_process_flag(0),

  _process_completed_buffers_threshold(SIZE_MAX),

  _buffer_enqueue_threshold(0)

{}

SATBMarkQueueSet::~SATBMarkQueueSet() {

  abandon_completed_buffers();

}

// _count_and_process_flag has flag in least significant bit, count in

// remaining bits.  _process_completed_buffers_threshold is scaled

// accordingly, with the lsbit set, so a _count_and_process_flag value

// is directly comparable with the recorded threshold value.  The

// process flag is set whenever the count exceeds the threshold, and

// remains set until the count is reduced to zero.

// Increment count.  If count > threshold, set flag, else maintain flag.

static void increment_count(volatile size_t* cfptr, size_t threshold) {

  size_t old;

  size_t value = Atomic::load(cfptr);

  do {

    old = value;

    value += 2;

    assert(value > old, "overflow");

    if (value > threshold) value |= 1;

    value = Atomic::cmpxchg(cfptr, old, value);

  } while (value != old);

}

// Decrement count.  If count == 0, clear flag, else maintain flag.

static void decrement_count(volatile size_t* cfptr) {

  size_t old;

  size_t value = Atomic::load(cfptr);

  do {

    assert((value >> 1) != 0, "underflow");

    old = value;

    value -= 2;

    if (value <= 1) value = 0;

    value = Atomic::cmpxchg(cfptr, old, value);

  } while (value != old);

}

void SATBMarkQueueSet::set_process_completed_buffers_threshold(size_t value) {

  // Scale requested threshold to align with count field.  If scaling

  // overflows, just use max value.  Set process flag field to make

  // comparison in increment_count exact.

  size_t scaled_value = value << 1;

  if ((scaled_value >> 1) != value) {

    scaled_value = SIZE_MAX;

  }

  _process_completed_buffers_threshold = scaled_value | 1;

}

void SATBMarkQueueSet::set_buffer_enqueue_threshold_percentage(uint value) {

  // Minimum threshold of 1 ensures enqueuing of completely full buffers.

  size_t size = buffer_size();

  size_t enqueue_qty = (size * value) / 100;

  _buffer_enqueue_threshold = MAX2(size - enqueue_qty, (size_t)1);

}

#ifdef ASSERT

void SATBMarkQueueSet::dump_active_states(bool expected_active) {

  log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");

  log_error(gc, verify)("Actual SATB active states:");

  log_error(gc, verify)("  Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");

  class DumpThreadStateClosure : public ThreadClosure {

    SATBMarkQueueSet* _qset;

  public:

    DumpThreadStateClosure(SATBMarkQueueSet* qset) : _qset(qset) {}

    virtual void do_thread(Thread* t) {

      SATBMarkQueue& queue = _qset->satb_queue_for_thread(t);

      log_error(gc, verify)("  Thread \"%s\" queue: %s",

                            t->name(),

                            queue.is_active() ? "ACTIVE" : "INACTIVE");

    }

  } closure(this);

  Threads::threads_do(&closure);

}

void SATBMarkQueueSet::verify_active_states(bool expected_active) {

  // Verify queue set state

  if (is_active() != expected_active) {

    dump_active_states(expected_active);

    fatal("SATB queue set has an unexpected active state");

  }

  // Verify thread queue states

  class VerifyThreadStatesClosure : public ThreadClosure {

    SATBMarkQueueSet* _qset;

    bool _expected_active;

  public:

    VerifyThreadStatesClosure(SATBMarkQueueSet* qset, bool expected_active) :

      _qset(qset), _expected_active(expected_active) {}

    virtual void do_thread(Thread* t) {

      if (_qset->satb_queue_for_thread(t).is_active() != _expected_active) {

        _qset->dump_active_states(_expected_active);

        fatal("Thread SATB queue has an unexpected active state");

      }

    }

  } closure(this, expected_active);

  Threads::threads_do(&closure);

}

#endif // ASSERT

void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {

  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");

#ifdef ASSERT

  verify_active_states(expected_active);

#endif // ASSERT

  // Update the global state, synchronized with threads list management.

  {

    MutexLocker ml(NonJavaThreadsList_lock, Mutex::_no_safepoint_check_flag);

    _all_active = active;

  }

  class SetThreadActiveClosure : public ThreadClosure {

    SATBMarkQueueSet* _qset;

    bool _active;

  public:

    SetThreadActiveClosure(SATBMarkQueueSet* qset, bool active) :

      _qset(qset), _active(active) {}

    virtual void do_thread(Thread* t) {

      _qset->satb_queue_for_thread(t).set_active(_active);

    }

  } closure(this, active);

  Threads::threads_do(&closure);

}

bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {

  BufferNode* nd = get_completed_buffer();

  if (nd != NULL) {

    void **buf = BufferNode::make_buffer_from_node(nd);

    size_t index = nd->index();

    size_t size = buffer_size();

    assert(index <= size, "invariant");

    cl->do_buffer(buf + index, size - index);

    deallocate_buffer(nd);

    return true;

  } else {

    return false;

  }

}

// SATB buffer life-cycle - Per-thread queues obtain buffers from the

// qset's buffer allocator, fill them, and push them onto the qset's

// list.  The GC concurrently pops buffers from the qset, processes

// them, and returns them to the buffer allocator for re-use.  Both

// the allocator and the qset use lock-free stacks.  The ABA problem

// is solved by having both allocation pops and GC pops performed

// within GlobalCounter critical sections, while the return of buffers

// to the allocator performs a GlobalCounter synchronize before

// pushing onto the allocator's list.

void SATBMarkQueueSet::enqueue_completed_buffer(BufferNode* node) {

  assert(node != NULL, "precondition");

  // Increment count and update flag appropriately.  Done before

  // pushing buffer so count is always at least the actual number in

  // the list, and decrement never underflows.

  increment_count(&_count_and_process_flag, _process_completed_buffers_threshold);

  _list.push(*node);

}

BufferNode* SATBMarkQueueSet::get_completed_buffer() {

  BufferNode* node;

  {

    GlobalCounter::CriticalSection cs(Thread::current());

    node = _list.pop();

  }

  if (node != NULL) {

    // Got a buffer so decrement count and update flag appropriately.

    decrement_count(&_count_and_process_flag);

  }

  return node;

}

#ifndef PRODUCT

// Helpful for debugging

#define SATB_PRINTER_BUFFER_SIZE 256

void SATBMarkQueueSet::print_all(const char* msg) {

  char buffer[SATB_PRINTER_BUFFER_SIZE];

  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");

  tty->cr();

  tty->print_cr("SATB BUFFERS [%s]", msg);

  BufferNode* nd = _list.top();

  int i = 0;

  while (nd != NULL) {

    void** buf = BufferNode::make_buffer_from_node(nd);

    os::snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);

    print_satb_buffer(buffer, buf, nd->index(), buffer_size());

    nd = nd->next();

    i += 1;

  }

  class PrintThreadClosure : public ThreadClosure {

    SATBMarkQueueSet* _qset;

    char* _buffer;

  public:

    PrintThreadClosure(SATBMarkQueueSet* qset, char* buffer) :

      _qset(qset), _buffer(buffer) {}

    virtual void do_thread(Thread* t) {

      os::snprintf(_buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());

      _qset->satb_queue_for_thread(t).print(_buffer);

    }

  } closure(this, buffer);

  Threads::threads_do(&closure);

  tty->cr();

}

#endif // PRODUCT

void SATBMarkQueueSet::abandon_completed_buffers() {

  Atomic::store(&_count_and_process_flag, size_t(0));

  BufferNode* buffers_to_delete = _list.pop_all();

  while (buffers_to_delete != NULL) {

    BufferNode* bn = buffers_to_delete;

    buffers_to_delete = bn->next();

    bn->set_next(NULL);

    deallocate_buffer(bn);

  }

}

void SATBMarkQueueSet::abandon_partial_marking() {

  assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");

  abandon_completed_buffers();

  class AbandonThreadQueueClosure : public ThreadClosure {

    SATBMarkQueueSet* _qset;

  public:

    AbandonThreadQueueClosure(SATBMarkQueueSet* qset) : _qset(qset) {}

    virtual void do_thread(Thread* t) {

      _qset->satb_queue_for_thread(t).reset();

    }

  } closure(this);

  Threads::threads_do(&closure);

}