markSweep.cpp

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/* Copyright 1994, 1995 LongView Technologies L.L.C. $Revision: 1.12 $ */
/* Copyright (c) 2006, Sun Microsystems, Inc.
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# include "incls/_precompiled.incl"
# include "incls/_markSweep.cpp.incl"

GrowableArray<memOop>* MarkSweep::stack;
GrowableArray<int>*    MarkSweep::hcode_offsets;
int                    MarkSweep::hcode_pos;

oop MarkSweep::collect(oop p) {
  FlagSetting  fl(GCInProgress, true);
  EventMarker  em("Garbage Collect");
  ResourceMark rm;
  TraceTime    t("Garbage collection", PrintGC);

  int old_used = Universe::old_gen.used();

  if (VerifyBeforeScavenge || VerifyBeforeGC) Universe::verify();

  // Clear all vm inline caches
  DeltaCallCache::clearAll();

  // clear remembered set; it is used for object sizes
  Universe::remembered_set->clear();

  allocate();   // allocate stack for traversal

  mark_sweep_phase1(&p);
  mark_sweep_phase2();
  mark_sweep_phase3();

  deallocate(); // clear allocated structures
  
  // clear the remember set; we have no pointers from old to new
  Universe::remembered_set->clear();

  lookupCache::flush();

  if (VerifyAfterScavenge || VerifyAfterGC) Universe::verify();

  if (PrintGC) {
    std->print(" %.1fM -> %.1fM",
               (double) old_used                 / (double) (1024 * 1024),
               (double) Universe::old_gen.used() / (double) (1024 * 1024));
  }

  return p;
}

void MarkSweep::allocate() {
  stack         = new GrowableArray<memOop>(200);
  hcode_offsets = new GrowableArray<int>(100);
  hcode_pos     = 0;
}

void MarkSweep::deallocate() {
  stack         = NULL;
  hcode_offsets = NULL;
}

void MarkSweep::trace(char* msg) {
  if (TraceGC)
    std->print("%s", msg);
}

memOop MarkSweep::reverse(oop* p) {
  oop obj = *p;

  // Return NULL if non memOop
  if (!obj->is_mem()) return NULL;
  
  if (memOop(obj)->is_gc_marked()) {
    // Reverse pointer
    *p = oop(memOop(obj)->mark());
    memOop(obj)->set_mark(p);

    return NULL;
  } else {
    // Before the pointer reversal takes place the object size must be made accessible
    // without using the klass pointer. We store the object size partially in the 
    // age field and partially in the remembered set.
    memOop(obj)->gc_store_size();

    assert(memOop(obj)->size() == memOop(obj)->gc_retrieve_size(), "checking real against stored size");

    // Reverse pointer
    *p = oop(memOop(obj)->mark());
    memOop(obj)->set_mark(p);

    assert(memOop(obj)->klass()->is_mem(), "just checking");

    return memOop(obj);
  }
}

void MarkSweep::reverse_and_push(oop* p) {
  memOop m = reverse(p);
  if (m) stack->push(m);
}

void MarkSweep::reverse_and_follow(oop* p) {
  memOop m = reverse(p);
  if (m) m->follow_contents(); // Follow contents of the marked object
}

void MarkSweep::follow_root(oop* p) {
  reverse_and_follow(p);
  while (!stack->isEmpty())
    stack->pop()->follow_contents();
}

void MarkSweep::add_hcode_offset(int offset) {
  hcode_offsets->push(offset);
}

int MarkSweep::next_hcode_offset() {
  return hcode_offsets->at(hcode_pos++);
}

void MarkSweep::mark_sweep_phase1(oop* p) {
  // Recursively traverse all live objects and mark them by reversing pointers.
  EventMarker em("1 reverse pointers");

  trace(" 1");

  WeakArrayRegister::begin_mark_sweep();
  Processes::convert_hcode_pointers();

  Universe::oops_do(&follow_root);

  // Hcode pointers point to the inside of methodOops and
  // have to be converted before we can follow the processes.
  Processes::follow_roots();

  WeakArrayRegister::check_and_follow_contents();
  NotificationQueue::oops_do(&follow_root);

  vmSymbols::follow_contents();

  // finalize unused objects - must be after all other gc_mark routines!
  Universe::symbol_table->follow_used_symbols();

  assert(stack->isEmpty(), "stack should be empty by now");
}

void MarkSweep::mark_sweep_phase2() {
  // Now all live objects are marked, compute the new object addresses.
  EventMarker em("2 compute new addresses");
  trace("2");

  OldWaterMark mark = Universe::old_gen.bottom_mark();
  // %note memory must be traversed in the same order as phase3
  Universe::old_gen.prepare_for_compaction(&mark);
  Universe::new_gen.prepare_for_compaction(&mark);
}

void MarkSweep::mark_sweep_phase3() {
  EventMarker em("3 compact heap");
  trace("3");
  OldWaterMark mark = Universe::old_gen.bottom_mark();
  mark._space->initialize_threshold();
  // %note memory must be traversed in the same order as phase2
  Universe::old_gen.compact(&mark);
  Universe::new_gen.compact(&mark);

  // All hcode pointers can now be restored. Remember
  // we converted these pointers in phase1.
  Processes::restore_hcode_pointers();
}

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