1 /*
   2  * Copyright (c) 1998, 2017, 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
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  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   inline static bool is_jweak(jobject handle);
  44   inline static oop& jobject_ref(jobject handle); // NOT jweak!
  45   inline static oop& jweak_ref(jobject handle);
  46 
  47   template<bool external_guard> inline static oop guard_value(oop value);
  48   template<bool external_guard> inline static oop resolve_impl(jobject handle);
  49   template<bool external_guard> static oop resolve_jweak(jweak handle);
  50 
  51  public:
  52   // Low tag bit in jobject used to distinguish a jweak.  jweak is
  53   // type equivalent to jobject, but there are places where we need to
  54   // be able to distinguish jweak values from other jobjects, and
  55   // is_weak_global_handle is unsuitable for performance reasons.  To
  56   // provide such a test we add weak_tag_value to the (aligned) byte
  57   // address designated by the jobject to produce the corresponding
  58   // jweak.  Accessing the value of a jobject must account for it
  59   // being a possibly offset jweak.
  60   static const uintptr_t weak_tag_size = 1;
  61   static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
  62   static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
  63   static const int weak_tag_value = 1;
  64 
  65   // Resolve handle into oop
  66   inline static oop resolve(jobject handle);
  67   // Resolve externally provided handle into oop with some guards
  68   inline static oop resolve_external_guard(jobject handle);
  69   // Resolve handle into oop, result guaranteed not to be null
  70   inline static oop resolve_non_null(jobject handle);
  71 
  72   // Local handles
  73   static jobject make_local(oop obj);
  74   static jobject make_local(JNIEnv* env, oop obj);    // Fast version when env is known
  75   static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
  76   inline static void destroy_local(jobject handle);
  77 
  78   // Global handles
  79   static jobject make_global(Handle  obj);
  80   static void destroy_global(jobject handle);
  81 
  82   // Weak global handles
  83   static jobject make_weak_global(Handle obj);
  84   static void destroy_weak_global(jobject handle);
  85 
  86   // Sentinel marking deleted handles in block. Note that we cannot store NULL as
  87   // the sentinel, since clearing weak global JNI refs are done by storing NULL in
  88   // the handle. The handle may not be reused before destroy_weak_global is called.
  89   static oop deleted_handle()   { return _deleted_handle; }
  90 
  91   // Initialization
  92   static void initialize();
  93 
  94   // Debugging
  95   static void print_on(outputStream* st);
  96   static void print()           { print_on(tty); }
  97   static void verify();
  98   static bool is_local_handle(Thread* thread, jobject handle);
  99   static bool is_frame_handle(JavaThread* thr, jobject obj);
 100   static bool is_global_handle(jobject handle);
 101   static bool is_weak_global_handle(jobject handle);
 102   static long global_handle_memory_usage();
 103   static long weak_global_handle_memory_usage();
 104 
 105   // Garbage collection support(global handles only, local handles are traversed from thread)
 106   // Traversal of regular global handles
 107   static void oops_do(OopClosure* f);
 108   // Traversal of weak global handles. Unreachable oops are cleared.
 109   static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
 110   // Traversal of weak global handles.
 111   static void weak_oops_do(OopClosure* f);
 112 };
 113 
 114 
 115 
 116 // JNI handle blocks holding local/global JNI handles
 117 
 118 class JNIHandleBlock : public CHeapObj<mtInternal> {
 119   friend class VMStructs;
 120   friend class CppInterpreter;
 121 
 122  private:
 123   enum SomeConstants {
 124     block_size_in_oops  = 32                    // Number of handles per handle block
 125   };
 126 
 127   oop             _handles[block_size_in_oops]; // The handles
 128   int             _top;                         // Index of next unused handle
 129   JNIHandleBlock* _next;                        // Link to next block
 130 
 131   // The following instance variables are only used by the first block in a chain.
 132   // Having two types of blocks complicates the code and the space overhead in negligble.
 133   JNIHandleBlock* _last;                        // Last block in use
 134   JNIHandleBlock* _pop_frame_link;              // Block to restore on PopLocalFrame call
 135   oop*            _free_list;                   // Handle free list
 136   int             _allocate_before_rebuild;     // Number of blocks to allocate before rebuilding free list
 137 
 138   // Check JNI, "planned capacity" for current frame (or push/ensure)
 139   size_t          _planned_capacity;
 140 
 141   #ifndef PRODUCT
 142   JNIHandleBlock* _block_list_link;             // Link for list below
 143   static JNIHandleBlock* _block_list;           // List of all allocated blocks (for debugging only)
 144   #endif
 145 
 146   static JNIHandleBlock* _block_free_list;      // Free list of currently unused blocks
 147   static int      _blocks_allocated;            // For debugging/printing
 148 
 149   // Fill block with bad_handle values
 150   void zap();
 151 
 152  protected:
 153   // No more handles in the both the current and following blocks
 154   void clear() { _top = 0; }
 155 
 156  private:
 157   // Free list computation
 158   void rebuild_free_list();
 159 
 160  public:
 161   // Handle allocation
 162   jobject allocate_handle(oop obj);
 163 
 164   // Block allocation and block free list management
 165   static JNIHandleBlock* allocate_block(Thread* thread = NULL);
 166   static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
 167 
 168   // JNI PushLocalFrame/PopLocalFrame support
 169   JNIHandleBlock* pop_frame_link() const          { return _pop_frame_link; }
 170   void set_pop_frame_link(JNIHandleBlock* block)  { _pop_frame_link = block; }
 171 
 172   // Stub generator support
 173   static int top_offset_in_bytes()                { return offset_of(JNIHandleBlock, _top); }
 174 
 175   // Garbage collection support
 176   // Traversal of regular handles
 177   void oops_do(OopClosure* f);
 178   // Traversal of weak handles. Unreachable oops are cleared.
 179   void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
 180 
 181   // Checked JNI support
 182   void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
 183   const size_t get_planned_capacity() { return _planned_capacity; }
 184   const size_t get_number_of_live_handles();
 185 
 186   // Debugging
 187   bool chain_contains(jobject handle) const;    // Does this block or following blocks contain handle
 188   bool contains(jobject handle) const;          // Does this block contain handle
 189   int length() const;                           // Length of chain starting with this block
 190   long memory_usage() const;
 191   #ifndef PRODUCT
 192   static bool any_contains(jobject handle);     // Does any block currently in use contain handle
 193   static void print_statistics();
 194   #endif
 195 };
 196 
 197 inline bool JNIHandles::is_jweak(jobject handle) {
 198   STATIC_ASSERT(weak_tag_size == 1);
 199   STATIC_ASSERT(weak_tag_value == 1);
 200   return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
 201 }
 202 
 203 inline oop& JNIHandles::jobject_ref(jobject handle) {
 204   assert(!is_jweak(handle), "precondition");
 205   return *reinterpret_cast<oop*>(handle);
 206 }
 207 
 208 inline oop& JNIHandles::jweak_ref(jobject handle) {
 209   assert(is_jweak(handle), "precondition");
 210   char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;
 211   return *reinterpret_cast<oop*>(ptr);
 212 }
 213 
 214 // external_guard is true if called from resolve_external_guard.
 215 // Treat deleted (and possibly zapped) as NULL for external_guard,
 216 // else as (asserted) error.
 217 template<bool external_guard>
 218 inline oop JNIHandles::guard_value(oop value) {
 219   if (!external_guard) {
 220     assert(value != badJNIHandle, "Pointing to zapped jni handle area");
 221     assert(value != deleted_handle(), "Used a deleted global handle");
 222   } else if ((value == badJNIHandle) || (value == deleted_handle())) {
 223     value = NULL;
 224   }
 225   return value;
 226 }
 227 
 228 // external_guard is true if called from resolve_external_guard.
 229 template<bool external_guard>
 230 inline oop JNIHandles::resolve_impl(jobject handle) {
 231   assert(handle != NULL, "precondition");
 232   oop result;
 233   if (is_jweak(handle)) {       // Unlikely
 234     result = resolve_jweak<external_guard>(handle);
 235   } else {
 236     result = jobject_ref(handle);
 237     // Construction of jobjects canonicalize a null value into a null
 238     // jobject, so for non-jweak the pointee should never be null.
 239     assert(external_guard || result != NULL,
 240            "Invalid value read from jni handle");
 241     result = guard_value<external_guard>(result);
 242   }
 243   return result;
 244 }
 245 
 246 inline oop JNIHandles::resolve(jobject handle) {
 247   oop result = NULL;
 248   if (handle != NULL) {
 249     result = resolve_impl<false /* external_guard */ >(handle);
 250   }
 251   return result;
 252 }
 253 
 254 // Resolve some erroneous cases to NULL, rather than treating them as
 255 // possibly unchecked errors.  In particular, deleted handles are
 256 // treated as NULL (though a deleted and later reallocated handle
 257 // isn't detected).
 258 inline oop JNIHandles::resolve_external_guard(jobject handle) {
 259   oop result = NULL;
 260   if (handle != NULL) {
 261     result = resolve_impl<true /* external_guard */ >(handle);
 262   }
 263   return result;
 264 }
 265 
 266 inline oop JNIHandles::resolve_non_null(jobject handle) {
 267   assert(handle != NULL, "JNI handle should not be null");
 268   oop result = resolve_impl<false /* external_guard */ >(handle);
 269   assert(result != NULL, "NULL read from jni handle");
 270   return result;
 271 }
 272 
 273 inline void JNIHandles::destroy_local(jobject handle) {
 274   if (handle != NULL) {
 275     jobject_ref(handle) = deleted_handle();
 276   }
 277 }
 278 
 279 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP