rSet.cpp

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/* Copyright 1994 - 1996 LongView Technologies L.L.C. $Revision: 1.32 $ */
/* Copyright (c) 2006, Sun Microsystems, Inc.
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# include "incls/_precompiled.incl"

# include <string.h>

# include "incls/_rSet.cpp.incl"

// values of bytes in byte map: during normal operation (incl. scavenge),
// bytes are either -1 (clean) or 0 (dirty); i.e., the interpreter / compiled code
// clear a byte when storing into that card.
// More precisely, the card being marked corrsponds to the object start, not
// necessarily to the word being updated (e.g., if the object starts towards the
// end of a card, the updated instance variable may be on the next card).  But for
// objArrays, the precise card is marked so that we don't need to scavenge the
// entire array.
// During GC, the bytes are used to remember object sizes, see comment further below

// To do list for the remembered set
//
// 1. Optimization suggested by Urs 9/30/95
//    Speed up card scanning by comparing words for frequent case
//    (A profile of Mark Sweep is necessary to make the call).
// 2. Handle objArrays in a more effficient way. Scavenge only
//    parts of the objArray with dirty cards.
//    The current implementation is REALLY slow for huge tenured objArrays
//    with few new pointers.

rSet::rSet() {
   low_boundary = Universe::new_gen.low_boundary;
  high_boundary = Universe::old_gen.high_boundary;
  clear(); 
  Set_Byte_Map_Base(byte_for(NULL));
  assert(byte_for(low_boundary) == byte_map, "Checking start of map");
}

void* rSet::operator new(size_t size) {
  assert((int(Universe::new_gen.low_boundary) & (card_size - 1)) == 0,
         "new must start at card boundary");
  assert((int(Universe::old_gen.low_boundary) & (card_size - 1)) == 0,
         "old must start at card boundary");
  assert((int(Universe::old_gen.high_boundary) & (card_size - 1)) == 0,
         "old must end at card boundary");
  assert(card_size >= 512, "card_size must be at least 512");
  int bmsize =
    (Universe::old_gen.high_boundary - Universe::new_gen.low_boundary)
      / card_size;
  return AllocateHeap(size + bmsize, "rSet");
}

// copy the bits from an older, smaller bitmap, add area [start,end)
rSet::rSet(rSet *old, char *start, char *end) {
  ShouldNotReachHere();
  /*
   low_boundary= Universe::new_gen.low_boundary;
  high_boundary= Universe::old_gen.high_boundary;
  char *old_low=  old->low_boundary;
  char *old_high= old->high_boundary;
  Set_Byte_Map_Base(byte_for(NULL));
  memcpy(byte_for(old_low),
         old->byte_for(old_low),
         old->byte_for(old_high) - old->byte_for(old_low));
  clear(byte_for(start), byte_for(end));
  delete old;
  */
}  

char* rSet::scavenge_contents(oldSpace* sp, char* begin, char* limit) {
  // make sure we are staring with a dirty page
  assert(!*begin, "check for dirty page");

  // Find object at page start

  oop* s = oop_for(begin);

  // Return if we're at the end.
  if (s >= sp->top()) return begin + 1;

  s = sp->object_start(s);

  char* end = begin+1;

  oop* object_end = NULL;

  while (!*end && end < limit) {
    while (!*end && end < limit) end++;

    // We now have a string of dirty pages [begin..end[
    oop* e = min(oop_for(end), (oop*)sp->top());

    if (e < (oop*)sp->top()) {
      // Find the object crossing the last dirty page
      object_end = sp->object_start(e);
      if (object_end != e) {
        // object starts on page boundary
        int size = as_memOop(object_end)->size();
        object_end += size;
      }
      end = byte_for(object_end);
    }
  }

  // Clear the cards
  for (char* i = begin; i < end; i++) *i = -1;

  // Find the end
  oop* e = min(oop_for(end), (oop*)sp->top());

  while (s < e) {
    memOop m = as_memOop(s);
    int size = m->scavenge_tenured_contents();
    assert(size = m->size(), "just checking");
    s += size;
  }
  return end;
}

void rSet::scavenge_contents(oldSpace* sp) {
  char* current_byte = byte_for(sp->bottom());
  char* end_byte     = byte_for(sp->top());
  // set sentinel for scan (dirty page)
  *(end_byte + 1) = 0;

  // scan over clean pages
  while (*current_byte) current_byte++;

  while (current_byte <= end_byte) {
    // Pass the dirty page on to scavenge_contents
    current_byte = scavenge_contents(sp, current_byte, end_byte);

    // scan over clean pages
    while (*current_byte) current_byte++;
  }
}

void rSet::print_set_for_space(oldSpace* sp) {
  char* current_byte = byte_for(sp->bottom());
  char* end_byte     = byte_for(sp->top());
  lprintf("%s: [%#lx, %#lx]\n", sp->name(), current_byte, end_byte);
  while (current_byte <= end_byte) {
    if (*current_byte) {
      lprintf("_");
    } else {
      lprintf("*");
    }
    current_byte++;
  }
  lprintf("\n");
}

int rSet::number_of_dirty_pages_in(oldSpace* sp) {
  int count = 0;
  char* current_byte = byte_for(sp->bottom());
  char* end_byte     = byte_for(sp->top());
  while (current_byte <= end_byte) {
    if (!*current_byte) count++;
    current_byte++;
  }
  return count;
}

class CheckDirtyClosure : public OopClosure {
 public:
  bool is_dirty;

  void clear() {
    is_dirty = false; 
  }

  void do_oop(oop* o) {
    if ((*o)->is_new()) {
      is_dirty = true;
      /*
      { FlagSetting fs(PrintObjectID, false);
        std->print("0x%lx ", o);
        (*o)->print_value();
        std->cr();
      }
      */
    }
  }
};

bool rSet::has_page_dirty_objects(oldSpace* sp, char* page) {
  // Find object at page start
  oop* s = sp->object_start(oop_for(page));
  // Find the end
  oop* e = min(oop_for(page+1), (oop*)sp->top());

  CheckDirtyClosure blk;

  while (s < e) {
    memOop m = as_memOop(s);
    blk.clear();
    m->oop_iterate(&blk);
    if (blk.is_dirty) return true;
    s += m->size();
  }
  return false;
}

int rSet::number_of_pages_with_dirty_objects_in(oldSpace* sp) {
  int count = 0;
  char* current_byte = byte_for(sp->bottom());
  char* end_byte     = byte_for(sp->top());
  while (current_byte <= end_byte) {
    if (has_page_dirty_objects(sp, current_byte))
      count++;
    current_byte++;
  }
  return count;
}

void rSet::print_set_for_object(memOop obj) {
  std->print("Remember set for 0x%lx ", obj);
  obj->print_value();
  std->cr();
  if (obj->is_new()) {
    std->print_cr(" object is in new space!");
  } else {
    std->sp();
    char* current_byte = byte_for(obj->addr());
    char* end_byte     = byte_for(obj->addr() + obj->size());
    while (current_byte <= end_byte) {
      if (*current_byte) {
        std->print("_");
      } else {
        std->print("*");
      }
      current_byte++;
    }
    std->cr();
  }
}

bool rSet::is_object_dirty(memOop obj) {
  assert(!obj->is_new(), "just checking");
  char* current_byte = byte_for(obj->addr());
  char* end_byte     = byte_for(obj->addr() + obj->size());
  while (current_byte <= end_byte) {
    if (*current_byte == 0) return true;
    current_byte++;
  }
  return false;
}

void rSet::clear(char *start, char *end) {
  int* from  = (int*) start;
  int  count = (int*) end - from;
  set_words(from, count, AllBits);
}

bool rSet::verify(bool postScavenge) {
  return true;
}

// Scheme for storing the size of objects during pointer-reversal phase of GC.
// (Can't get object size via klass because pointers are reversed! :-)
// size must be >= 128.
// 1. byte     Size            Size
// [0..128[ -> [128..256[
// 128      -> 1 extra byte   [256      .. 256   + 2^8 [
// 129      -> 2 extra bytes  [512      .. 512   + 2^16[
// 130      -> 4 extra bytes  [66048    ..         2^32[

const int lim_0 =         markOopDesc::max_age;
const int lim_1 =         (1 <<  8);
const int lim_2 = lim_1 + (1 <<  8);
const int lim_3 = lim_2 + (1 << 16);

void rSet::set_size(memOop obj, int size) {
  unsigned char* p = (unsigned char*) byte_for(obj->addr());
  assert(size >= lim_0, "size must be >= max_age");
  if (size < lim_1) {           // use 1 byte
    *p = (unsigned char) (size - lim_0);
  } else if (size < lim_2) {    // use 1 + 1 bytes
    *p++ = lim_0 + 2;
    *p   = (unsigned char) (size - lim_1);
  } else if (size < lim_3) {    // use 1 + 2 bytes
    *p++ = lim_0 + 3;
    *(unsigned short*)p = (unsigned short) (size - lim_2);
  } else {                      // use 1 + 4 bytes
    *p++ = lim_0 + 4;
    *(unsigned int*)p = (unsigned int) (size - lim_3);
  }
}

int rSet::get_size(memOop obj) {
  unsigned char* p = (unsigned char*) byte_for(obj->addr());
  unsigned char h = *p++;
  if (h <= lim_0 + 1) return h + lim_0;
  if (h == lim_0 + 2) return (*(unsigned char*)  p) + lim_1;
  if (h == lim_0 + 3) return (*(unsigned short*) p) + lim_2;
  if (h == lim_0 + 4) return (*(unsigned int*)   p) + lim_3;
  ShouldNotReachHere();
  return 0;
}

// new old space added; fix the cards
void rSet::fixup(char *start, char *end) {
  if (end > high_boundary) {
    Universe::remembered_set = new rSet(this, start, end);
  } else {
    clear(byte_for(start), byte_for(end));
  }
}

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