src/hotspot/share/code/dependencyContext.hpp

/*
 * Copyright (c) 2015, 2020, 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.
 *
 */

#ifndef SHARE_VM_CODE_DEPENDENCYCONTEXT_HPP
#define SHARE_VM_CODE_DEPENDENCYCONTEXT_HPP

#include "memory/allocation.hpp"
#include "oops/oop.hpp"
#include "runtime/handles.hpp"
#include "runtime/perfData.hpp"
#include "runtime/safepoint.hpp"

class nmethod;
class DepChange;

//
// nmethodBucket is used to record dependent nmethods for
// deoptimization.  nmethod dependencies are actually <klass, method>
// pairs but we really only care about the klass part for purposes of
// finding nmethods which might need to be deoptimized.  Instead of
// recording the method, a count of how many times a particular nmethod
// was recorded is kept.  This ensures that any recording errors are
// noticed since an nmethod should be removed as many times are it's
// added.
//
class nmethodBucket: public CHeapObj<mtClass> {
  friend class VMStructs;
 private:
  nmethod*       _nmethod;
  int            _count;
  nmethodBucket* _next;

 public:
  nmethodBucket(nmethod* nmethod, nmethodBucket* next) :
   _nmethod(nmethod), _next(next), _count(1) {}

  int count()                             { return _count; }
  int increment()                         { _count += 1; return _count; }
  int decrement();
  nmethodBucket* next()                   { return _next; }
  void set_next(nmethodBucket* b)         { _next = b; }
  nmethod* get_nmethod()                  { return _nmethod; }
};

//
// Utility class to manipulate nmethod dependency context.
// The context consists of nmethodBucket* (a head of a linked list)
// and a boolean flag (does the list contains stale entries). The structure is
// encoded as an intptr_t: lower bit is used for the flag. It is possible since
// nmethodBucket* is aligned - the structure is malloc'ed in C heap.
// Dependency context can be attached either to an InstanceKlass (_dep_context field)
// or CallSiteContext oop for call_site_target dependencies (see javaClasses.hpp).
// DependencyContext class operates on some location which holds a intptr_t value.
//
class DependencyContext : public StackObj {
  friend class VMStructs;
  friend class TestDependencyContext;
 private:
  enum TagBits { _has_stale_entries_bit = 1, _has_stale_entries_mask = 1 };

  intptr_t* _dependency_context_addr;

  void set_dependencies(nmethodBucket* b) {
    assert((intptr_t(b) & _has_stale_entries_mask) == 0, "should be aligned");
    if (has_stale_entries()) {
      *_dependency_context_addr = intptr_t(b) | _has_stale_entries_mask;
    } else {
      *_dependency_context_addr = intptr_t(b);
    }
  }

  void set_has_stale_entries(bool x) {
    if (x) {
      *_dependency_context_addr |= _has_stale_entries_mask;
    } else {
      *_dependency_context_addr &= ~_has_stale_entries_mask;
    }
  }

  nmethodBucket* dependencies() {
    intptr_t value = *_dependency_context_addr;
    return (nmethodBucket*) (value & ~_has_stale_entries_mask);
  }

  bool has_stale_entries() const {
    intptr_t value = *_dependency_context_addr;
    return (value & _has_stale_entries_mask) != 0;
  }

  static PerfCounter* _perf_total_buckets_allocated_count;
  static PerfCounter* _perf_total_buckets_deallocated_count;
  static PerfCounter* _perf_total_buckets_stale_count;
  static PerfCounter* _perf_total_buckets_stale_acc_count;

 public:
#ifdef ASSERT
  // Safepoints are forbidden during DC lifetime. GC can invalidate
  // _dependency_context_addr if it relocates the holder
  // (e.g. CallSiteContext Java object).
  int _safepoint_counter;

  DependencyContext(intptr_t* addr) : _dependency_context_addr(addr),
    _safepoint_counter(SafepointSynchronize::_safepoint_counter) {}

  ~DependencyContext() {
    assert(_safepoint_counter == SafepointSynchronize::_safepoint_counter, "safepoint happened");
  }
#else
  DependencyContext(intptr_t* addr) : _dependency_context_addr(addr) {}
#endif // ASSERT

  static const intptr_t EMPTY = 0; // dependencies = NULL, has_stale_entries = false

  static void init();

  int  mark_dependent_nmethods(DepChange& changes);
  void add_dependent_nmethod(nmethod* nm, bool expunge_stale_entries = false);
  void remove_dependent_nmethod(nmethod* nm, bool expunge_stale_entries = false);
  int  remove_all_dependents();

  void expunge_stale_entries();

  // Unsafe deallocation of nmethodBuckets. Used in IK::release_C_heap_structures
  // to clean up the context possibly containing live entries pointing to unloaded nmethods.
  void wipe();

#ifndef PRODUCT
  void print_dependent_nmethods(bool verbose);
#endif //PRODUCT
  bool is_dependent_nmethod(nmethod* nm);
  bool find_stale_entries();
};
#endif // SHARE_VM_CODE_DEPENDENCYCONTEXT_HPP