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Java example source code file (loaderConstraints.cpp)

This example Java source code file (loaderConstraints.cpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

classloaderdata, classloaderdata\:\:class_loader_data, free_c_heap_array, handle, hashtable, instanceklass\:\:cast, klass, loaderconstraintentry, null, purging, resourcemark, symbol, systemdictionary\:\:loader_name, traceloaderconstraints

The loaderConstraints.cpp Java example source code

/*
 * 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

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