1 /* 2 * Copyright 1998-2010 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 20 * CA 95054 USA or visit www.sun.com if you need additional information or 21 * have any questions. 22 * 23 */ 24 25 class JNIHandleBlock; 26 27 28 // Interface for creating and resolving local/global JNI handles 29 30 class JNIHandles : AllStatic { 31 friend class VMStructs; 32 private: 33 static JNIHandleBlock* _global_handles; // First global handle block 34 static JNIHandleBlock* _weak_global_handles; // First weak global handle block 35 static oop _deleted_handle; // Sentinel marking deleted handles 36 37 public: 38 // Resolve handle into oop 39 inline static oop resolve(jobject handle); 40 // Resolve externally provided handle into oop with some guards 41 inline static oop resolve_external_guard(jobject handle); 42 // Resolve handle into oop, result guaranteed not to be null 43 inline static oop resolve_non_null(jobject handle); 44 45 // Local handles 46 static jobject make_local(oop obj); 47 static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known 48 static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known 49 inline static void destroy_local(jobject handle); 50 51 // Global handles 52 static jobject make_global(Handle obj); 53 static void destroy_global(jobject handle); 54 55 // Weak global handles 56 static jobject make_weak_global(Handle obj); 57 static void destroy_weak_global(jobject handle); 58 59 // jmethodID handling (as Weak global handles). 60 // Because the useful life-span of a jmethodID cannot be determined, once created they are 61 // never reclaimed. The methods to which they refer, however, can be GC'ed away if the class 62 // is unloaded or if the method is made obsolete or deleted -- in these cases, the jmethodID 63 // refers to NULL (as is the case for any weak reference). 64 static jmethodID make_jmethod_id(methodHandle mh); 65 static void destroy_jmethod_id(jmethodID mid); 66 // Use resolve_jmethod_id() in situations where the caller is expected 67 // to provide a valid jmethodID; the only sanity checks are in asserts; 68 // result guaranteed not to be NULL. 69 inline static methodOop resolve_jmethod_id(jmethodID mid); 70 // Use checked_resolve_jmethod_id() in situations where the caller 71 // should provide a valid jmethodID, but might not. NULL is returned 72 // when the jmethodID does not refer to a valid method. 73 inline static methodOop checked_resolve_jmethod_id(jmethodID mid); 74 static void change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh); 75 76 // Sentinel marking deleted handles in block. Note that we cannot store NULL as 77 // the sentinel, since clearing weak global JNI refs are done by storing NULL in 78 // the handle. The handle may not be reused before destroy_weak_global is called. 79 static oop deleted_handle() { return _deleted_handle; } 80 81 // Initialization 82 static void initialize(); 83 84 // Debugging 85 static void print_on(outputStream* st); 86 static void print() { print_on(tty); } 87 static void verify(); 88 static bool is_local_handle(Thread* thread, jobject handle); 89 static bool is_frame_handle(JavaThread* thr, jobject obj); 90 static bool is_global_handle(jobject handle); 91 static bool is_weak_global_handle(jobject handle); 92 static long global_handle_memory_usage(); 93 static long weak_global_handle_memory_usage(); 94 95 // Garbage collection support(global handles only, local handles are traversed from thread) 96 // Traversal of regular global handles 97 static void oops_do(OopClosure* f); 98 // Traversal of weak global handles. Unreachable oops are cleared. 99 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f); 100 }; 101 102 103 104 // JNI handle blocks holding local/global JNI handles 105 106 class JNIHandleBlock : public CHeapObj { 107 friend class VMStructs; 108 private: 109 enum SomeConstants { 110 block_size_in_oops = 32 // Number of handles per handle block 111 }; 112 113 oop _handles[block_size_in_oops]; // The handles 114 int _top; // Index of next unused handle 115 JNIHandleBlock* _next; // Link to next block 116 117 // The following instance variables are only used by the first block in a chain. 118 // Having two types of blocks complicates the code and the space overhead in negligble. 119 JNIHandleBlock* _last; // Last block in use 120 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call 121 oop* _free_list; // Handle free list 122 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list 123 124 #ifndef PRODUCT 125 JNIHandleBlock* _block_list_link; // Link for list below 126 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only) 127 #endif 128 129 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks 130 static int _blocks_allocated; // For debugging/printing 131 132 // Fill block with bad_handle values 133 void zap(); 134 135 // No more handles in the both the current and following blocks 136 void clear() { _top = 0; } 137 138 // Free list computation 139 void rebuild_free_list(); 140 141 public: 142 // Handle allocation 143 jobject allocate_handle(oop obj); 144 145 // Block allocation and block free list management 146 static JNIHandleBlock* allocate_block(Thread* thread = NULL); 147 static void release_block(JNIHandleBlock* block, Thread* thread = NULL); 148 149 // JNI PushLocalFrame/PopLocalFrame support 150 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; } 151 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; } 152 153 // Stub generator support 154 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); } 155 156 // Garbage collection support 157 // Traversal of regular handles 158 void oops_do(OopClosure* f); 159 // Traversal of weak handles. Unreachable oops are cleared. 160 void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f); 161 162 // Debugging 163 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle 164 bool contains(jobject handle) const; // Does this block contain handle 165 int length() const; // Length of chain starting with this block 166 long memory_usage() const; 167 #ifndef PRODUCT 168 static bool any_contains(jobject handle); // Does any block currently in use contain handle 169 static void print_statistics(); 170 #endif 171 }; 172 173 174 inline oop JNIHandles::resolve(jobject handle) { 175 oop result = (handle == NULL ? (oop)NULL : *(oop*)handle); 176 assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle"); 177 assert(result != badJNIHandle, "Pointing to zapped jni handle area"); 178 return result; 179 }; 180 181 182 inline oop JNIHandles::resolve_external_guard(jobject handle) { 183 if (handle == NULL) return NULL; 184 oop result = *(oop*)handle; 185 if (result == NULL || result == badJNIHandle) return NULL; 186 return result; 187 }; 188 189 190 inline oop JNIHandles::resolve_non_null(jobject handle) { 191 assert(handle != NULL, "JNI handle should not be null"); 192 oop result = *(oop*)handle; 193 assert(result != NULL, "Invalid value read from jni handle"); 194 assert(result != badJNIHandle, "Pointing to zapped jni handle area"); 195 // Don't let that private _deleted_handle object escape into the wild. 196 assert(result != deleted_handle(), "Used a deleted global handle."); 197 return result; 198 }; 199 200 inline methodOop JNIHandles::resolve_jmethod_id(jmethodID mid) { 201 return (methodOop) resolve_non_null((jobject)mid); 202 }; 203 204 inline methodOop JNIHandles::checked_resolve_jmethod_id(jmethodID mid) { 205 oop o = resolve_external_guard((jobject) mid); 206 if (o == NULL || !o->is_method()) { 207 return (methodOop) NULL; 208 } 209 210 return (methodOop) o; 211 }; 212 213 214 inline void JNIHandles::destroy_local(jobject handle) { 215 if (handle != NULL) { 216 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it 217 } 218 }