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 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_RUNTIME_JNIHANDLES_HPP 26 #define SHARE_VM_RUNTIME_JNIHANDLES_HPP 27 28 #include "memory/allocation.hpp" 29 #include "runtime/handles.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 negligible. 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 // Free list computation 153 void rebuild_free_list(); 154 155 // No more handles in the both the current and following blocks 156 void clear() { _top = 0; } 157 158 public: 159 // Handle allocation 160 jobject allocate_handle(oop obj); 161 162 // Release Handle 163 void release_handle(jobject); 164 165 // Block allocation and block free list management 166 static JNIHandleBlock* allocate_block(Thread* thread = NULL); 167 static void release_block(JNIHandleBlock* block, Thread* thread = NULL); 168 169 // JNI PushLocalFrame/PopLocalFrame support 170 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; } 171 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; } 172 173 // Stub generator support 174 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); } 175 176 // Garbage collection support 177 // Traversal of regular handles 178 void oops_do(OopClosure* f); 179 // Traversal of weak handles. Unreachable oops are cleared. 180 void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f); 181 182 // Checked JNI support 183 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; } 184 const size_t get_planned_capacity() { return _planned_capacity; } 185 const size_t get_number_of_live_handles(); 186 187 // Debugging 188 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle 189 bool contains(jobject handle) const; // Does this block contain handle 190 int length() const; // Length of chain starting with this block 191 long memory_usage() const; 192 #ifndef PRODUCT 193 static bool any_contains(jobject handle); // Does any block currently in use contain handle 194 static void print_statistics(); 195 #endif 196 }; 197 198 inline bool JNIHandles::is_jweak(jobject handle) { 199 STATIC_ASSERT(weak_tag_size == 1); 200 STATIC_ASSERT(weak_tag_value == 1); 201 return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0; 202 } 203 204 inline oop& JNIHandles::jobject_ref(jobject handle) { 205 assert(!is_jweak(handle), "precondition"); 206 return *reinterpret_cast<oop*>(handle); 207 } 208 209 inline oop& JNIHandles::jweak_ref(jobject handle) { 210 assert(is_jweak(handle), "precondition"); 211 char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value; 212 return *reinterpret_cast<oop*>(ptr); 213 } 214 215 // external_guard is true if called from resolve_external_guard. 216 // Treat deleted (and possibly zapped) as NULL for external_guard, 217 // else as (asserted) error. 218 template<bool external_guard> 219 inline oop JNIHandles::guard_value(oop value) { 220 if (!external_guard) { 221 assert(value != badJNIHandle, "Pointing to zapped jni handle area"); 222 assert(value != deleted_handle(), "Used a deleted global handle"); 223 } else if ((value == badJNIHandle) || (value == deleted_handle())) { 224 value = NULL; 225 } 226 return value; 227 } 228 229 // external_guard is true if called from resolve_external_guard. 230 template<bool external_guard> 231 inline oop JNIHandles::resolve_impl(jobject handle) { 232 assert(handle != NULL, "precondition"); 233 oop result; 234 if (is_jweak(handle)) { // Unlikely 235 result = resolve_jweak<external_guard>(handle); 236 } else { 237 result = jobject_ref(handle); 238 // Construction of jobjects canonicalize a null value into a null 239 // jobject, so for non-jweak the pointee should never be null. 240 assert(external_guard || result != NULL, 241 "Invalid value read from jni handle"); 242 result = guard_value<external_guard>(result); 243 } 244 return result; 245 } 246 247 inline oop JNIHandles::resolve(jobject handle) { 248 oop result = NULL; 249 if (handle != NULL) { 250 result = resolve_impl<false /* external_guard */ >(handle); 251 } 252 return result; 253 } 254 255 // Resolve some erroneous cases to NULL, rather than treating them as 256 // possibly unchecked errors. In particular, deleted handles are 257 // treated as NULL (though a deleted and later reallocated handle 258 // isn't detected). 259 inline oop JNIHandles::resolve_external_guard(jobject handle) { 260 oop result = NULL; 261 if (handle != NULL) { 262 result = resolve_impl<true /* external_guard */ >(handle); 263 } 264 return result; 265 } 266 267 inline oop JNIHandles::resolve_non_null(jobject handle) { 268 assert(handle != NULL, "JNI handle should not be null"); 269 oop result = resolve_impl<false /* external_guard */ >(handle); 270 assert(result != NULL, "NULL read from jni handle"); 271 return result; 272 } 273 274 inline void JNIHandles::destroy_local(jobject handle) { 275 if (handle != NULL) { 276 jobject_ref(handle) = deleted_handle(); 277 } 278 } 279 280 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP