1 /*
2 * Copyright 1998-2009 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 inline static methodOop resolve_jmethod_id(jmethodID mid);
67 inline static methodOop checked_resolve_jmethod_id(jmethodID mid); // NULL on invalid jmethodID
68 static void change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh);
69
70 // Sentinel marking deleted handles in block. Note that we cannot store NULL as
71 // the sentinel, since clearing weak global JNI refs are done by storing NULL in
72 // the handle. The handle may not be reused before destroy_weak_global is called.
73 static oop deleted_handle() { return _deleted_handle; }
74
75 // Initialization
76 static void initialize();
77
78 // Debugging
79 static void print_on(outputStream* st);
80 static void print() { print_on(tty); }
81 static void verify();
82 static bool is_local_handle(Thread* thread, jobject handle);
83 static bool is_frame_handle(JavaThread* thr, jobject obj);
84 static bool is_global_handle(jobject handle);
85 static bool is_weak_global_handle(jobject handle);
86 static long global_handle_memory_usage();
87 static long weak_global_handle_memory_usage();
88
89 // Garbage collection support(global handles only, local handles are traversed from thread)
90 // Traversal of regular global handles
91 static void oops_do(OopClosure* f);
92 // Traversal of weak global handles. Unreachable oops are cleared.
93 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
94 };
95
96
97
98 // JNI handle blocks holding local/global JNI handles
99
100 class JNIHandleBlock : public CHeapObj {
101 friend class VMStructs;
102 private:
103 enum SomeConstants {
104 block_size_in_oops = 32 // Number of handles per handle block
105 };
106
107 oop _handles[block_size_in_oops]; // The handles
108 int _top; // Index of next unused handle
109 JNIHandleBlock* _next; // Link to next block
110
111 // The following instance variables are only used by the first block in a chain.
112 // Having two types of blocks complicates the code and the space overhead in negligble.
113 JNIHandleBlock* _last; // Last block in use
114 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
115 oop* _free_list; // Handle free list
116 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
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 // No more handles in the both the current and following blocks
130 void clear() { _top = 0; }
131
132 // Free list computation
133 void rebuild_free_list();
134
135 public:
136 // Handle allocation
137 jobject allocate_handle(oop obj);
138
139 // Block allocation and block free list management
140 static JNIHandleBlock* allocate_block(Thread* thread = NULL);
141 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
142
143 // JNI PushLocalFrame/PopLocalFrame support
144 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
145 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
146
147 // Stub generator support
148 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
149
150 // Garbage collection support
151 // Traversal of regular handles
152 void oops_do(OopClosure* f);
153 // Traversal of weak handles. Unreachable oops are cleared.
154 void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
155
156 // Debugging
157 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
158 bool contains(jobject handle) const; // Does this block contain handle
159 int length() const; // Length of chain starting with this block
160 long memory_usage() const;
161 #ifndef PRODUCT
162 static bool any_contains(jobject handle); // Does any block currently in use contain handle
163 static void print_statistics();
164 #endif
165 };
166
167
168 inline oop JNIHandles::resolve(jobject handle) {
169 oop result = (handle == NULL ? (oop)NULL : *(oop*)handle);
170 assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle");
171 assert(result != badJNIHandle, "Pointing to zapped jni handle area");
172 return result;
173 };
174
175
176 inline oop JNIHandles::resolve_external_guard(jobject handle) {
177 if (handle == NULL) return NULL;
178 oop result = *(oop*)handle;
179 if (result == NULL || result == badJNIHandle) return NULL;
180 return result;
181 };
182
183
184 inline oop JNIHandles::resolve_non_null(jobject handle) {
185 assert(handle != NULL, "JNI handle should not be null");
186 oop result = *(oop*)handle;
187 assert(result != NULL, "Invalid value read from jni handle");
188 assert(result != badJNIHandle, "Pointing to zapped jni handle area");
189 // Don't let that private _deleted_handle object escape into the wild.
190 assert(result != deleted_handle(), "Used a deleted global handle.");
191 return result;
192 };
193
194 inline methodOop JNIHandles::resolve_jmethod_id(jmethodID mid) {
195 return (methodOop) resolve_non_null((jobject)mid);
196 };
197
198 inline methodOop JNIHandles::checked_resolve_jmethod_id(jmethodID mid) {
199 if (mid == NULL) {
200 return (methodOop) NULL;
201 }
202
203 oop o = resolve_non_null((jobject) mid);
204 if (!o->is_method()) {
205 return (methodOop) NULL;
206 }
207
208 return (methodOop) o;
209 };
210
211
212 inline void JNIHandles::destroy_local(jobject handle) {
213 if (handle != NULL) {
214 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
215 }
216 }