vm/classfile/loaderConstraints.cpp

/*
 * Copyright (c) 2003, 2012, 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 "classfile/classLoaderData.inline.hpp"
#include "classfile/loaderConstraints.hpp"
#include "memory/resourceArea.hpp"
#include "oops/oop.inline.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/safepoint.hpp"
#include "utilities/hashtable.inline.hpp"

void LoaderConstraintEntry::set_loader(int i, oop p) {
  set_loader_data(i, ClassLoaderData::class_loader_data(p));
}

LoaderConstraintTable::LoaderConstraintTable(int nof_buckets)
  : Hashtable<Klass*, mtClass>(nof_buckets, sizeof(LoaderConstraintEntry)) {};


LoaderConstraintEntry* LoaderConstraintTable::new_entry(
                                 unsigned int hash, Symbol* name,
                                 Klass* klass, int num_loaders,
                                 int max_loaders) {
  LoaderConstraintEntry* entry;
  entry = (LoaderConstraintEntry*)Hashtable<Klass*, mtClass>::new_entry(hash, klass);
  entry->set_name(name);
  entry->set_num_loaders(num_loaders);
  entry->set_max_loaders(max_loaders);
  return entry;
}

void LoaderConstraintTable::free_entry(LoaderConstraintEntry *entry) {
  // decrement name refcount before freeing
  entry->name()->decrement_refcount();
  Hashtable<Klass*, mtClass>::free_entry(entry);
}

// Enhanced Class Redefinition support
void LoaderConstraintTable::classes_do(KlassClosure* f) {
  for (int index = 0; index < table_size(); index++) {
    for (LoaderConstraintEntry* probe = bucket(index);
                                probe != NULL;
                                probe = probe->next()) {
      if (probe->klass() != NULL) {
        f->do_klass(probe->klass());
      }
        }
      }
    }

// The loaderConstraintTable must always be accessed with the
// SystemDictionary lock held. This is true even for readers as
// entries in the table could be being dynamically resized.

LoaderConstraintEntry** LoaderConstraintTable::find_loader_constraint(
                                    Symbol* name, Handle loader) {

  unsigned int hash = compute_hash(name);
  int index = hash_to_index(hash);
  LoaderConstraintEntry** pp = bucket_addr(index);
  ClassLoaderData* loader_data = ClassLoaderData::class_loader_data(loader());

  while (*pp) {
    LoaderConstraintEntry* p = *pp;
    if (p->hash() == hash) {
      if (p->name() == name) {
        for (int i = p->num_loaders() - 1; i >= 0; i--) {
          if (p->loader_data(i) == loader_data) {
            return pp;
          }
        }
      }
    }
    pp = p->next_addr();
  }
  return pp;
}


void LoaderConstraintTable::purge_loader_constraints() {
  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
  // Remove unloaded entries from constraint table
  for (int index = 0; index < table_size(); index++) {
    LoaderConstraintEntry** p = bucket_addr(index);
    while(*p) {
      LoaderConstraintEntry* probe = *p;
      Klass* klass = probe->klass();
      // Remove klass that is no longer alive
      if (klass != NULL &&
          klass->class_loader_data()->is_unloading()) {
        probe->set_klass(NULL);
        if (TraceLoaderConstraints) {
          ResourceMark rm;
          tty->print_cr("[Purging class object from constraint for name %s,"
                     " loader list:",
                     probe->name()->as_C_string());
          for (int i = 0; i < probe->num_loaders(); i++) {
            tty->print_cr("[   [%d]: %s", i,
                          probe->loader_data(i)->loader_name());
          }
        }
      }
      // Remove entries no longer alive from loader array
      int n = 0;
      while (n < probe->num_loaders()) {
        if (probe->loader_data(n)->is_unloading()) {
            if (TraceLoaderConstraints) {
              ResourceMark rm;
              tty->print_cr("[Purging loader %s from constraint for name %s",
                            probe->loader_data(n)->loader_name(),
                            probe->name()->as_C_string()
                            );
            }

            // Compact array
            int num = probe->num_loaders() - 1;
            probe->set_num_loaders(num);
          probe->set_loader_data(n, probe->loader_data(num));
          probe->set_loader_data(num, NULL);

            if (TraceLoaderConstraints) {
              ResourceMark rm;
              tty->print_cr("[New loader list:");
              for (int i = 0; i < probe->num_loaders(); i++) {
                tty->print_cr("[   [%d]: %s", i,
                              probe->loader_data(i)->loader_name());
              }
            }

            continue;  // current element replaced, so restart without
                       // incrementing n
          }
        n++;
      }
      // Check whether entry should be purged
      if (probe->num_loaders() < 2) {
            if (TraceLoaderConstraints) {
              ResourceMark rm;
              tty->print("[Purging complete constraint for name %s\n",
                         probe->name()->as_C_string());
            }

        // Purge entry
        *p = probe->next();
        FREE_C_HEAP_ARRAY(oop, probe->loaders(), mtClass);
        free_entry(probe);
      } else {
#ifdef ASSERT
        if (probe->klass() != NULL) {
          ClassLoaderData* loader_data =
            probe->klass()->class_loader_data();
          assert(!loader_data->is_unloading(), "klass should be live");
        }
#endif
        // Go to next entry
        p = probe->next_addr();
      }
    }
  }
}

bool LoaderConstraintTable::add_entry(Symbol* class_name,
                                      Klass* klass1, Handle class_loader1,
                                      Klass* klass2, Handle class_loader2) {
  int failure_code = 0; // encode different reasons for failing

  if (klass1 != NULL && klass2 != NULL && klass1 != klass2) {
    failure_code = 1;
  } else {
    Klass* klass = klass1 != NULL ? klass1 : klass2;

    LoaderConstraintEntry** pp1 = find_loader_constraint(class_name,
                                                         class_loader1);
    if (*pp1 != NULL && (*pp1)->klass() != NULL) {
      if (klass != NULL) {
        if (klass != (*pp1)->klass()) {
          failure_code = 2;
        }
      } else {
        klass = (*pp1)->klass();
      }
    }

    LoaderConstraintEntry** pp2 = find_loader_constraint(class_name,
                                                         class_loader2);
    if (*pp2 != NULL && (*pp2)->klass() != NULL) {
      if (klass != NULL) {
        if (klass != (*pp2)->klass()) {
          failure_code = 3;
        }
      } else {
        klass = (*pp2)->klass();
      }
    }

    if (failure_code == 0) {
      if (*pp1 == NULL && *pp2 == NULL) {
        unsigned int hash = compute_hash(class_name);
        int index = hash_to_index(hash);
        LoaderConstraintEntry* p;
        p = new_entry(hash, class_name, klass, 2, 2);
        p->set_loaders(NEW_C_HEAP_ARRAY(ClassLoaderData*, 2, mtClass));
        p->set_loader(0, class_loader1());
        p->set_loader(1, class_loader2());
        p->set_klass(klass);
        p->set_next(bucket(index));
        set_entry(index, p);
        if (TraceLoaderConstraints) {
          ResourceMark rm;
          tty->print("[Adding new constraint for name: %s, loader[0]: %s,"
                     " loader[1]: %s ]\n",
                     class_name->as_C_string(),
                     SystemDictionary::loader_name(class_loader1()),
                     SystemDictionary::loader_name(class_loader2())
                     );
        }
      } else if (*pp1 == *pp2) {
        /* constraint already imposed */
        if ((*pp1)->klass() == NULL) {
          (*pp1)->set_klass(klass);
          if (TraceLoaderConstraints) {
            ResourceMark rm;
            tty->print("[Setting class object in existing constraint for"
                       " name: %s and loader %s ]\n",
                       class_name->as_C_string(),
                       SystemDictionary::loader_name(class_loader1())
                       );
          }
        } else {
          assert((*pp1)->klass() == klass, "loader constraints corrupted");
        }
      } else if (*pp1 == NULL) {
        extend_loader_constraint(*pp2, class_loader1, klass);
      } else if (*pp2 == NULL) {
        extend_loader_constraint(*pp1, class_loader2, klass);
      } else {
        merge_loader_constraints(pp1, pp2, klass);
      }
    }
  }

  if (failure_code != 0 && TraceLoaderConstraints) {
    ResourceMark rm;
    const char* reason = "";
    switch(failure_code) {
    case 1: reason = "the class objects presented by loader[0] and loader[1]"
              " are different"; break;
    case 2: reason = "the class object presented by loader[0] does not match"
              " the stored class object in the constraint"; break;
    case 3: reason = "the class object presented by loader[1] does not match"
              " the stored class object in the constraint"; break;
    default: reason = "unknown reason code";
    }
    tty->print("[Failed to add constraint for name: %s, loader[0]: %s,"
               " loader[1]: %s, Reason: %s ]\n",
               class_name->as_C_string(),
               SystemDictionary::loader_name(class_loader1()),
               SystemDictionary::loader_name(class_loader2()),
               reason
               );
  }

  return failure_code == 0;
}


// return true if the constraint was updated, false if the constraint is
// violated
bool LoaderConstraintTable::check_or_update(instanceKlassHandle k,
                                                   Handle loader,
                                                   Symbol* name) {
  LoaderConstraintEntry* p = *(find_loader_constraint(name, loader));
  if (p && p->klass() != NULL && p->klass() != k()) {
    if (TraceLoaderConstraints) {
      ResourceMark rm;
      tty->print("[Constraint check failed for name %s, loader %s: "
                 "the presented class object differs from that stored ]\n",
                 name->as_C_string(),
                 SystemDictionary::loader_name(loader()));
    }
    return false;
  } else {
    if (p && p->klass() == NULL) {
      p->set_klass(k());
      if (TraceLoaderConstraints) {
        ResourceMark rm;
        tty->print("[Updating constraint for name %s, loader %s, "
                   "by setting class object ]\n",
                   name->as_C_string(),
                   SystemDictionary::loader_name(loader()));
      }
    }
    return true;
  }
}

Klass* LoaderConstraintTable::find_constrained_klass(Symbol* name,
                                                       Handle loader) {
  LoaderConstraintEntry *p = *(find_loader_constraint(name, loader));
  if (p != NULL && p->klass() != NULL) {
    if (p->klass()->oop_is_instance() && !InstanceKlass::cast(p->klass())->is_loaded()) {
      // Only return fully loaded classes.  Classes found through the
      // constraints might still be in the process of loading.
      return NULL;
    }
    return p->klass();
  }

  // No constraints, or else no klass loaded yet.
  return NULL;
}

void LoaderConstraintTable::ensure_loader_constraint_capacity(
                                                     LoaderConstraintEntry *p,
                                                    int nfree) {
    if (p->max_loaders() - p->num_loaders() < nfree) {
        int n = nfree + p->num_loaders();
        ClassLoaderData** new_loaders = NEW_C_HEAP_ARRAY(ClassLoaderData*, n, mtClass);
        memcpy(new_loaders, p->loaders(), sizeof(ClassLoaderData*) * p->num_loaders());
        p->set_max_loaders(n);
        FREE_C_HEAP_ARRAY(ClassLoaderData*, p->loaders(), mtClass);
        p->set_loaders(new_loaders);
    }
}


void LoaderConstraintTable::extend_loader_constraint(LoaderConstraintEntry* p,
                                                     Handle loader,
                                                     Klass* klass) {
  ensure_loader_constraint_capacity(p, 1);
  int num = p->num_loaders();
  p->set_loader(num, loader());
  p->set_num_loaders(num + 1);
  if (TraceLoaderConstraints) {
    ResourceMark rm;
    tty->print("[Extending constraint for name %s by adding loader[%d]: %s %s",
               p->name()->as_C_string(),
               num,
               SystemDictionary::loader_name(loader()),
               (p->klass() == NULL ? " and setting class object ]\n" : " ]\n")
               );
  }
  if (p->klass() == NULL) {
    p->set_klass(klass);
  } else {
    assert(klass == NULL || p->klass() == klass, "constraints corrupted");
  }
}


void LoaderConstraintTable::merge_loader_constraints(
                                                   LoaderConstraintEntry** pp1,
                                                   LoaderConstraintEntry** pp2,
                                                   Klass* klass) {
  // make sure *pp1 has higher capacity
  if ((*pp1)->max_loaders() < (*pp2)->max_loaders()) {
    LoaderConstraintEntry** tmp = pp2;
    pp2 = pp1;
    pp1 = tmp;
  }

  LoaderConstraintEntry* p1 = *pp1;
  LoaderConstraintEntry* p2 = *pp2;

  ensure_loader_constraint_capacity(p1, p2->num_loaders());

  for (int i = 0; i < p2->num_loaders(); i++) {
    int num = p1->num_loaders();
    p1->set_loader_data(num, p2->loader_data(i));
    p1->set_num_loaders(num + 1);
  }

  if (TraceLoaderConstraints) {
    ResourceMark rm;
    tty->print_cr("[Merged constraints for name %s, new loader list:",
                  p1->name()->as_C_string()
                  );

    for (int i = 0; i < p1->num_loaders(); i++) {
      tty->print_cr("[   [%d]: %s", i,
                    p1->loader_data(i)->loader_name());
    }
    if (p1->klass() == NULL) {
      tty->print_cr("[... and setting class object]");
    }
  }

  // p1->klass() will hold NULL if klass, p2->klass(), and old
  // p1->klass() are all NULL.  In addition, all three must have
  // matching non-NULL values, otherwise either the constraints would
  // have been violated, or the constraints had been corrupted (and an
  // assertion would fail).
  if (p2->klass() != NULL) {
    assert(p2->klass() == klass, "constraints corrupted");
  }
  if (p1->klass() == NULL) {
    p1->set_klass(klass);
  } else {
    assert(p1->klass() == klass, "constraints corrupted");
  }

  *pp2 = p2->next();
  FREE_C_HEAP_ARRAY(oop, p2->loaders(), mtClass);
  free_entry(p2);
  return;
}


void LoaderConstraintTable::verify(Dictionary* dictionary,
                                   PlaceholderTable* placeholders) {
  Thread *thread = Thread::current();
  for (int cindex = 0; cindex < _loader_constraint_size; cindex++) {
    for (LoaderConstraintEntry* probe = bucket(cindex);
                                probe != NULL;
                                probe = probe->next()) {
      if (probe->klass() != NULL) {
        InstanceKlass* ik = InstanceKlass::cast(probe->klass());
        guarantee(ik->name() == probe->name(), "name should match");
        Symbol* name = ik->name();
        ClassLoaderData* loader_data = ik->class_loader_data();
        unsigned int d_hash = dictionary->compute_hash(name, loader_data);
        int d_index = dictionary->hash_to_index(d_hash);
        Klass* k = dictionary->find_class(d_index, d_hash, name, loader_data);
        if (k != NULL) {
          // We found the class in the system dictionary, so we should
          // make sure that the Klass* matches what we already have.
          guarantee(k == probe->klass(), "klass should be in dictionary");
        } else {
          // If we don't find the class in the system dictionary, it
          // has to be in the placeholders table.
          unsigned int p_hash = placeholders->compute_hash(name, loader_data);
          int p_index = placeholders->hash_to_index(p_hash);
          PlaceholderEntry* entry = placeholders->get_entry(p_index, p_hash,
                                                            name, loader_data);

          // The InstanceKlass might not be on the entry, so the only
          // thing we can check here is whether we were successful in
          // finding the class in the placeholders table.
          guarantee(entry != NULL, "klass should be in the placeholders");
        }
      }
      for (int n = 0; n< probe->num_loaders(); n++) {
        assert(ClassLoaderDataGraph::contains_loader_data(probe->loader_data(n)), "The loader is missing");
      }
    }
  }
}

#ifndef PRODUCT

// Called with the system dictionary lock held
void LoaderConstraintTable::print() {
  ResourceMark rm;

  assert_locked_or_safepoint(SystemDictionary_lock);
  tty->print_cr("Java loader constraints (entries=%d)", _loader_constraint_size);
  for (int cindex = 0; cindex < _loader_constraint_size; cindex++) {
    for (LoaderConstraintEntry* probe = bucket(cindex);
                                probe != NULL;
                                probe = probe->next()) {
      tty->print("%4d: ", cindex);
      probe->name()->print();
      tty->print(" , loaders:");
      for (int n = 0; n < probe->num_loaders(); n++) {
        probe->loader_data(n)->print_value();
        tty->print(", ");
      }
      tty->cr();
    }
  }
}
#endif