1 /*
   2  * Copyright (c) 1998, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_RUNTIME_JNIHANDLES_HPP
  26 #define SHARE_VM_RUNTIME_JNIHANDLES_HPP
  27 
  28 #include "runtime/handles.hpp"
  29 #include "utilities/top.hpp"
  30 
  31 class JNIHandleBlock;
  32 
  33 
  34 // Interface for creating and resolving local/global JNI handles
  35 
  36 class JNIHandles : AllStatic {
  37   friend class VMStructs;
  38  private:
  39   static JNIHandleBlock* _global_handles;             // First global handle block
  40   static JNIHandleBlock* _weak_global_handles;        // First weak global handle block
  41   static oop _deleted_handle;                         // Sentinel marking deleted handles
  42 
  43  public:
  44   // Resolve handle into oop
  45   inline static oop resolve(jobject handle);
  46   // Resolve externally provided handle into oop with some guards
  47   inline static oop resolve_external_guard(jobject handle);
  48   // Resolve handle into oop, result guaranteed not to be null
  49   inline static oop resolve_non_null(jobject handle);
  50 
  51   // Local handles
  52   static jobject make_local(oop obj);
  53   static jobject make_local(JNIEnv* env, oop obj);    // Fast version when env is known
  54   static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
  55   inline static void destroy_local(jobject handle);
  56 
  57   // Global handles
  58   static jobject make_global(Handle  obj);
  59   static void destroy_global(jobject handle);
  60 
  61   // Weak global handles
  62   static jobject make_weak_global(Handle obj);
  63   static void destroy_weak_global(jobject handle);
  64 
  65   // Sentinel marking deleted handles in block. Note that we cannot store NULL as
  66   // the sentinel, since clearing weak global JNI refs are done by storing NULL in
  67   // the handle. The handle may not be reused before destroy_weak_global is called.
  68   static oop deleted_handle()   { return _deleted_handle; }
  69 
  70   // Initialization
  71   static void initialize();
  72 
  73   // Debugging
  74   static void print_on(outputStream* st);
  75   static void print()           { print_on(tty); }
  76   static void verify();
  77   static bool is_local_handle(Thread* thread, jobject handle);
  78   static bool is_frame_handle(JavaThread* thr, jobject obj);
  79   static bool is_global_handle(jobject handle);
  80   static bool is_weak_global_handle(jobject handle);
  81   static long global_handle_memory_usage();
  82   static long weak_global_handle_memory_usage();
  83 
  84   // Garbage collection support(global handles only, local handles are traversed from thread)
  85   // Traversal of regular global handles
  86   static void oops_do(OopClosure* f);
  87   // Traversal of weak global handles. Unreachable oops are cleared.
  88   static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
  89 };
  90 
  91 
  92 
  93 // JNI handle blocks holding local/global JNI handles
  94 
  95 class JNIHandleBlock : public CHeapObj<mtInternal> {
  96   friend class VMStructs;
  97   friend class CppInterpreter;
  98 
  99  private:
 100   enum SomeConstants {
 101     block_size_in_oops  = 32                    // Number of handles per handle block
 102   };
 103 
 104   oop             _handles[block_size_in_oops]; // The handles
 105   int             _top;                         // Index of next unused handle
 106   JNIHandleBlock* _next;                        // Link to next block
 107 
 108   // The following instance variables are only used by the first block in a chain.
 109   // Having two types of blocks complicates the code and the space overhead in negligble.
 110   JNIHandleBlock* _last;                        // Last block in use
 111   JNIHandleBlock* _pop_frame_link;              // Block to restore on PopLocalFrame call
 112   oop*            _free_list;                   // Handle free list
 113   int             _allocate_before_rebuild;     // Number of blocks to allocate before rebuilding free list
 114 
 115   #ifndef PRODUCT
 116   JNIHandleBlock* _block_list_link;             // Link for list below
 117   static JNIHandleBlock* _block_list;           // List of all allocated blocks (for debugging only)
 118   #endif
 119 
 120   static JNIHandleBlock* _block_free_list;      // Free list of currently unused blocks
 121   static int      _blocks_allocated;            // For debugging/printing
 122 
 123   // Fill block with bad_handle values
 124   void zap();
 125 
 126  protected:
 127   // No more handles in the both the current and following blocks
 128   void clear() { _top = 0; }
 129 
 130  private:
 131   // Free list computation
 132   void rebuild_free_list();
 133 
 134  public:
 135   // Handle allocation
 136   jobject allocate_handle(oop obj);
 137 
 138   // Block allocation and block free list management
 139   static JNIHandleBlock* allocate_block(Thread* thread = NULL);
 140   static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
 141 
 142   // JNI PushLocalFrame/PopLocalFrame support
 143   JNIHandleBlock* pop_frame_link() const          { return _pop_frame_link; }
 144   void set_pop_frame_link(JNIHandleBlock* block)  { _pop_frame_link = block; }
 145 
 146   // Stub generator support
 147   static int top_offset_in_bytes()                { return offset_of(JNIHandleBlock, _top); }
 148 
 149   // Garbage collection support
 150   // Traversal of regular handles
 151   void oops_do(OopClosure* f);
 152   // Traversal of weak handles. Unreachable oops are cleared.
 153   void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
 154 
 155   // Debugging
 156   bool chain_contains(jobject handle) const;    // Does this block or following blocks contain handle
 157   bool contains(jobject handle) const;          // Does this block contain handle
 158   int length() const;                           // Length of chain starting with this block
 159   long memory_usage() const;
 160   #ifndef PRODUCT
 161   static bool any_contains(jobject handle);     // Does any block currently in use contain handle
 162   static void print_statistics();
 163   #endif
 164 };
 165 
 166 
 167 inline oop JNIHandles::resolve(jobject handle) {
 168   oop result = (handle == NULL ? (oop)NULL : *(oop*)handle);
 169   assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle");
 170   assert(result != badJNIHandle, "Pointing to zapped jni handle area");
 171   return result;
 172 };
 173 
 174 
 175 inline oop JNIHandles::resolve_external_guard(jobject handle) {
 176   if (handle == NULL) return NULL;
 177   oop result = *(oop*)handle;
 178   if (result == NULL || result == badJNIHandle) return NULL;
 179   return result;
 180 };
 181 
 182 
 183 inline oop JNIHandles::resolve_non_null(jobject handle) {
 184   assert(handle != NULL, "JNI handle should not be null");
 185   oop result = *(oop*)handle;
 186   assert(result != NULL, "Invalid value read from jni handle");
 187   assert(result != badJNIHandle, "Pointing to zapped jni handle area");
 188   // Don't let that private _deleted_handle object escape into the wild.
 189   assert(result != deleted_handle(), "Used a deleted global handle.");
 190   return result;
 191 };
 192 
 193 inline void JNIHandles::destroy_local(jobject handle) {
 194   if (handle != NULL) {
 195     *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
 196   }
 197 }
 198 
 199 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP