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 /*

  * Copyright (c) 1998, 2010, 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

  public:

   // 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);

   // jmethodID handling (as Weak global handles).

   // Because the useful life-span of a jmethodID cannot be determined, once created they are

   // never reclaimed.  The methods to which they refer, however, can be GC'ed away if the class

   // is unloaded or if the method is made obsolete or deleted -- in these cases, the jmethodID

   // refers to NULL (as is the case for any weak reference).

   static jmethodID make_jmethod_id(methodHandle mh);

   static void destroy_jmethod_id(jmethodID mid);

   // Use resolve_jmethod_id() in situations where the caller is expected

   // to provide a valid jmethodID; the only sanity checks are in asserts;

   // result guaranteed not to be NULL.

   inline static methodOop resolve_jmethod_id(jmethodID mid);

   // Use checked_resolve_jmethod_id() in situations where the caller

   // should provide a valid jmethodID, but might not. NULL is returned

   // when the jmethodID does not refer to a valid method.

   inline static methodOop checked_resolve_jmethod_id(jmethodID mid);

   static void change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh);

   // 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);

 };

 // JNI handle blocks holding local/global JNI handles

 class JNIHandleBlock : public CHeapObj {

   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

   #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);

   // 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 oop JNIHandles::resolve(jobject handle) {

   oop result = (handle == NULL ? (oop)NULL : *(oop*)handle);

   assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle");

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

   return result;

 };

 inline oop JNIHandles::resolve_external_guard(jobject handle) {

   if (handle == NULL) return NULL;

   oop result = *(oop*)handle;

   if (result == NULL || result == badJNIHandle) return NULL;

   return result;

 };

 inline oop JNIHandles::resolve_non_null(jobject handle) {

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

   oop result = *(oop*)handle;

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

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

   // Don't let that private _deleted_handle object escape into the wild.

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

   return result;

 };

 inline methodOop JNIHandles::resolve_jmethod_id(jmethodID mid) {

   return (methodOop) resolve_non_null((jobject)mid);

 };

 inline methodOop JNIHandles::checked_resolve_jmethod_id(jmethodID mid) {

   oop o = resolve_external_guard((jobject) mid);

   if (o == NULL || !o->is_method()) {

     return (methodOop) NULL;

   }

   return (methodOop) o;

 };

 inline void JNIHandles::destroy_local(jobject handle) {

   if (handle != NULL) {

     *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it

   }

 }

 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP