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 /*

  * 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

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 #ifndef SHARE_VM_RUNTIME_JNIHANDLES_HPP

 #define SHARE_VM_RUNTIME_JNIHANDLES_HPP

 #include "runtime/handles.hpp"

 #include "utilities/top.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 negligble.

   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();

  protected:

   // No more handles in the both the current and following blocks

   void clear() { _top = 0; }

  private:

   // Free list computation

   void rebuild_free_list();

  public:

   // Handle allocation

   jobject allocate_handle(oop obj);

   // 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