1 /* 2 * Copyright (c) 1998, 2014, 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 size_t 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 negligible. 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 // Check JNI, "planned capacity" for current frame (or push/ensure) 116 size_t _planned_capacity; 117 118 #ifndef PRODUCT 119 JNIHandleBlock* _block_list_link; // Link for list below 120 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only) 121 #endif 122 123 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks 124 static int _blocks_allocated; // For debugging/printing 125 126 // Fill block with bad_handle values 127 void zap(); 128 129 protected: 130 // No more handles in the both the current and following blocks 131 void clear() { _top = 0; } 132 133 private: 134 // Free list computation 135 void rebuild_free_list(); 136 137 public: 138 // Handle allocation 139 jobject allocate_handle(oop obj); 140 141 // Block allocation and block free list management 142 static JNIHandleBlock* allocate_block(Thread* thread = NULL); 143 static void release_block(JNIHandleBlock* block, Thread* thread = NULL); 144 145 // JNI PushLocalFrame/PopLocalFrame support 146 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; } 147 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; } 148 149 // Stub generator support 150 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); } 151 152 // Garbage collection support 153 // Traversal of regular handles 154 void oops_do(OopClosure* f); 155 // Traversal of weak handles. Unreachable oops are cleared. 156 size_t weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f); 157 158 // Checked JNI support 159 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; } 160 const size_t get_planned_capacity() { return _planned_capacity; } 161 const size_t get_number_of_live_handles(); 162 163 // Debugging 164 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle 165 bool contains(jobject handle) const; // Does this block contain handle 166 int length() const; // Length of chain starting with this block 167 long memory_usage() const; 168 #ifndef PRODUCT 169 static bool any_contains(jobject handle); // Does any block currently in use contain handle 170 static void print_statistics(); 171 #endif 172 }; 173 174 175 inline oop JNIHandles::resolve(jobject handle) { 176 oop result = (handle == NULL ? (oop)NULL : *(oop*)handle); 177 assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle"); 178 assert(result != badJNIHandle, "Pointing to zapped jni handle area"); 179 return result; 180 }; 181 182 183 inline oop JNIHandles::resolve_external_guard(jobject handle) { 184 if (handle == NULL) return NULL; 185 oop result = *(oop*)handle; 186 if (result == NULL || result == badJNIHandle) return NULL; 187 return result; 188 }; 189 190 191 inline oop JNIHandles::resolve_non_null(jobject handle) { 192 assert(handle != NULL, "JNI handle should not be null"); 193 oop result = *(oop*)handle; 194 assert(result != NULL, "Invalid value read from jni handle"); 195 assert(result != badJNIHandle, "Pointing to zapped jni handle area"); 196 // Don't let that private _deleted_handle object escape into the wild. 197 assert(result != deleted_handle(), "Used a deleted global handle."); 198 return result; 199 }; 200 201 inline void JNIHandles::destroy_local(jobject handle) { 202 if (handle != NULL) { 203 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it 204 } 205 } 206 207 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP