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.
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19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 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 // Release Handle
165 void release_handle(jobject);
166
167 // Block allocation and block free list management
168 static JNIHandleBlock* allocate_block(Thread* thread = NULL);
169 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
170
171 // JNI PushLocalFrame/PopLocalFrame support
172 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
173 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
174
175 // Stub generator support
176 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
177
178 // Garbage collection support
179 // Traversal of regular handles
180 void oops_do(OopClosure* f);
181 // Traversal of weak handles. Unreachable oops are cleared.
182 void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
183
184 // Checked JNI support
185 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
186 const size_t get_planned_capacity() { return _planned_capacity; }
187 const size_t get_number_of_live_handles();
188
189 // Debugging
190 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
191 bool contains(jobject handle) const; // Does this block contain handle
192 int length() const; // Length of chain starting with this block
193 long memory_usage() const;
194 #ifndef PRODUCT
195 static bool any_contains(jobject handle); // Does any block currently in use contain handle
196 static void print_statistics();
197 #endif
198 };
199
200 inline bool JNIHandles::is_jweak(jobject handle) {
201 STATIC_ASSERT(weak_tag_size == 1);
202 STATIC_ASSERT(weak_tag_value == 1);
203 return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
204 }
205
206 inline oop& JNIHandles::jobject_ref(jobject handle) {
207 assert(!is_jweak(handle), "precondition");
208 return *reinterpret_cast<oop*>(handle);
209 }
210
211 inline oop& JNIHandles::jweak_ref(jobject handle) {
212 assert(is_jweak(handle), "precondition");
213 char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;
214 return *reinterpret_cast<oop*>(ptr);
215 }
216
217 // external_guard is true if called from resolve_external_guard.
218 // Treat deleted (and possibly zapped) as NULL for external_guard,
219 // else as (asserted) error.
220 template<bool external_guard>
221 inline oop JNIHandles::guard_value(oop value) {
222 if (!external_guard) {
223 assert(value != badJNIHandle, "Pointing to zapped jni handle area");
224 assert(value != deleted_handle(), "Used a deleted global handle");
225 } else if ((value == badJNIHandle) || (value == deleted_handle())) {
226 value = NULL;
227 }
228 return value;
229 }
230
231 // external_guard is true if called from resolve_external_guard.
232 template<bool external_guard>
233 inline oop JNIHandles::resolve_impl(jobject handle) {
234 assert(handle != NULL, "precondition");
235 oop result;
236 if (is_jweak(handle)) { // Unlikely
237 result = resolve_jweak<external_guard>(handle);
238 } else {
239 result = jobject_ref(handle);
240 // Construction of jobjects canonicalize a null value into a null
241 // jobject, so for non-jweak the pointee should never be null.
242 assert(external_guard || result != NULL,
243 "Invalid value read from jni handle");
244 result = guard_value<external_guard>(result);
245 }
246 return result;
247 }
248
249 inline oop JNIHandles::resolve(jobject handle) {
250 oop result = NULL;
251 if (handle != NULL) {
252 result = resolve_impl<false /* external_guard */ >(handle);
253 }
254 return result;
255 }
256
257 // Resolve some erroneous cases to NULL, rather than treating them as
258 // possibly unchecked errors. In particular, deleted handles are
259 // treated as NULL (though a deleted and later reallocated handle
260 // isn't detected).
261 inline oop JNIHandles::resolve_external_guard(jobject handle) {
262 oop result = NULL;
263 if (handle != NULL) {
264 result = resolve_impl<true /* external_guard */ >(handle);
265 }
266 return result;
267 }
268
269 inline oop JNIHandles::resolve_non_null(jobject handle) {
270 assert(handle != NULL, "JNI handle should not be null");
271 oop result = resolve_impl<false /* external_guard */ >(handle);
272 assert(result != NULL, "NULL read from jni handle");
273 return result;
274 }
275
276 inline void JNIHandles::destroy_local(jobject handle) {
277 if (handle != NULL) {
278 jobject_ref(handle) = deleted_handle();
279 }
280 }
281
282 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP