/*

 * Copyright (c) 1998, 2017, 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.

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 */

#ifndef SHARE_VM_RUNTIME_JNIHANDLES_HPP

#define SHARE_VM_RUNTIME_JNIHANDLES_HPP

#include "memory/allocation.hpp"

#include "runtime/handles.hpp"

class JNIHandleBlock;

// Interface for creating and resolving local/global JNI handles

class JNIHandles : AllStatic {

  friend class VMStructs;

 private:

  static JNIHandleBlock* _global_handles;             // First global handle block

  static JNIHandleBlock* _weak_global_handles;        // First weak global handle block

  static oop _deleted_handle;                         // Sentinel marking deleted handles

  inline static bool is_jweak(jobject handle);

  inline static oop& jobject_ref(jobject handle); // NOT jweak!

  inline static oop& jweak_ref(jobject handle);

  template<bool external_guard> inline static oop guard_value(oop value);

  template<bool external_guard> inline static oop resolve_impl(jobject handle);

  template<bool external_guard> static oop resolve_jweak(jweak handle);

 public:

  // Low tag bit in jobject used to distinguish a jweak.  jweak is

  // type equivalent to jobject, but there are places where we need to

  // be able to distinguish jweak values from other jobjects, and

  // is_weak_global_handle is unsuitable for performance reasons.  To

  // provide such a test we add weak_tag_value to the (aligned) byte

  // address designated by the jobject to produce the corresponding

  // jweak.  Accessing the value of a jobject must account for it

  // being a possibly offset jweak.

  static const uintptr_t weak_tag_size = 1;

  static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);

  static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;

  static const int weak_tag_value = 1;

  // Resolve handle into oop

  inline static oop resolve(jobject handle);

  // Resolve externally provided handle into oop with some guards

  inline static oop resolve_external_guard(jobject handle);

  // Resolve handle into oop, result guaranteed not to be null

  inline static oop resolve_non_null(jobject handle);

  // Local handles

  static jobject make_local(oop obj);

  static jobject make_local(JNIEnv* env, oop obj);    // Fast version when env is known

  static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known

  inline static void destroy_local(jobject handle);

  // Global handles

  static jobject make_global(Handle  obj);

  static void destroy_global(jobject handle);

  // Weak global handles

  static jobject make_weak_global(Handle obj);

  static void destroy_weak_global(jobject handle);

  // Sentinel marking deleted handles in block. Note that we cannot store NULL as

  // the sentinel, since clearing weak global JNI refs are done by storing NULL in

  // the handle. The handle may not be reused before destroy_weak_global is called.

  static oop deleted_handle()   { return _deleted_handle; }

  // Initialization

  static void initialize();

  // Debugging

  static void print_on(outputStream* st);

  static void print()           { print_on(tty); }

  static void verify();

  static bool is_local_handle(Thread* thread, jobject handle);

  static bool is_frame_handle(JavaThread* thr, jobject obj);

  static bool is_global_handle(jobject handle);

  static bool is_weak_global_handle(jobject handle);

  static long global_handle_memory_usage();

  static long weak_global_handle_memory_usage();

  // Garbage collection support(global handles only, local handles are traversed from thread)

  // Traversal of regular global handles

  static void oops_do(OopClosure* f);

  // Traversal of weak global handles. Unreachable oops are cleared.

  static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);

  // Traversal of weak global handles.

  static void weak_oops_do(OopClosure* f);

};

// JNI handle blocks holding local/global JNI handles

class JNIHandleBlock : public CHeapObj<mtInternal> {

  friend class VMStructs;

  friend class CppInterpreter;

 private:

  enum SomeConstants {

    block_size_in_oops  = 32                    // Number of handles per handle block

  };

  oop             _handles[block_size_in_oops]; // The handles

  int             _top;                         // Index of next unused handle

  JNIHandleBlock* _next;                        // Link to next block

  // The following instance variables are only used by the first block in a chain.

  // Having two types of blocks complicates the code and the space overhead in negligible.

  JNIHandleBlock* _last;                        // Last block in use

  JNIHandleBlock* _pop_frame_link;              // Block to restore on PopLocalFrame call

  oop*            _free_list;                   // Handle free list

  int             _allocate_before_rebuild;     // Number of blocks to allocate before rebuilding free list

  // Check JNI, "planned capacity" for current frame (or push/ensure)

  size_t          _planned_capacity;

  #ifndef PRODUCT

  JNIHandleBlock* _block_list_link;             // Link for list below

  static JNIHandleBlock* _block_list;           // List of all allocated blocks (for debugging only)

  #endif

  static JNIHandleBlock* _block_free_list;      // Free list of currently unused blocks

  static int      _blocks_allocated;            // For debugging/printing

  // Fill block with bad_handle values

  void zap();

  // Free list computation

  void rebuild_free_list();

 public:

  // Handle allocation

  jobject allocate_handle(oop obj);

  // Release Handle

  void release_handle(jobject);

  // Block allocation and block free list management

  static JNIHandleBlock* allocate_block(Thread* thread = NULL);

  static void release_block(JNIHandleBlock* block, Thread* thread = NULL);

  // JNI PushLocalFrame/PopLocalFrame support

  JNIHandleBlock* pop_frame_link() const          { return _pop_frame_link; }

  void set_pop_frame_link(JNIHandleBlock* block)  { _pop_frame_link = block; }

  // Stub generator support

  static int top_offset_in_bytes()                { return offset_of(JNIHandleBlock, _top); }

  // Garbage collection support

  // Traversal of regular handles

  void oops_do(OopClosure* f);

  // Traversal of weak handles. Unreachable oops are cleared.

  void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);

  // Checked JNI support

  void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }

  const size_t get_planned_capacity() { return _planned_capacity; }

  const size_t get_number_of_live_handles();

  // Debugging

  bool chain_contains(jobject handle) const;    // Does this block or following blocks contain handle

  bool contains(jobject handle) const;          // Does this block contain handle

  int length() const;                           // Length of chain starting with this block

  long memory_usage() const;

  #ifndef PRODUCT

  static bool any_contains(jobject handle);     // Does any block currently in use contain handle

  static void print_statistics();

  #endif

};

inline bool JNIHandles::is_jweak(jobject handle) {

  STATIC_ASSERT(weak_tag_size == 1);

  STATIC_ASSERT(weak_tag_value == 1);

  return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;

}

inline oop& JNIHandles::jobject_ref(jobject handle) {

  assert(!is_jweak(handle), "precondition");

  return *reinterpret_cast<oop*>(handle);

}

inline oop& JNIHandles::jweak_ref(jobject handle) {

  assert(is_jweak(handle), "precondition");

  char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;

  return *reinterpret_cast<oop*>(ptr);

}

// external_guard is true if called from resolve_external_guard.

// Treat deleted (and possibly zapped) as NULL for external_guard,

// else as (asserted) error.

template<bool external_guard>

inline oop JNIHandles::guard_value(oop value) {

  if (!external_guard) {

    assert(value != badJNIHandle, "Pointing to zapped jni handle area");

    assert(value != deleted_handle(), "Used a deleted global handle");

  } else if ((value == badJNIHandle) || (value == deleted_handle())) {

    value = NULL;

  }

  return value;

}

// external_guard is true if called from resolve_external_guard.

template<bool external_guard>

inline oop JNIHandles::resolve_impl(jobject handle) {

  assert(handle != NULL, "precondition");

  oop result;

  if (is_jweak(handle)) {       // Unlikely

    result = resolve_jweak<external_guard>(handle);

  } else {

    result = jobject_ref(handle);

    // Construction of jobjects canonicalize a null value into a null

    // jobject, so for non-jweak the pointee should never be null.

    assert(external_guard || result != NULL,

           "Invalid value read from jni handle");

    result = guard_value<external_guard>(result);

  }

  return result;

}

inline oop JNIHandles::resolve(jobject handle) {

  oop result = NULL;

  if (handle != NULL) {

    result = resolve_impl<false /* external_guard */ >(handle);

  }

  return result;

}

// Resolve some erroneous cases to NULL, rather than treating them as

// possibly unchecked errors.  In particular, deleted handles are

// treated as NULL (though a deleted and later reallocated handle

// isn't detected).

inline oop JNIHandles::resolve_external_guard(jobject handle) {

  oop result = NULL;

  if (handle != NULL) {

    result = resolve_impl<true /* external_guard */ >(handle);

  }

  return result;

}

inline oop JNIHandles::resolve_non_null(jobject handle) {

  assert(handle != NULL, "JNI handle should not be null");

  oop result = resolve_impl<false /* external_guard */ >(handle);

  assert(result != NULL, "NULL read from jni handle");

  return result;

}

inline void JNIHandles::destroy_local(jobject handle) {

  if (handle != NULL) {

    jobject_ref(handle) = deleted_handle();

  }

}

#endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP