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 // This method is not inlined in order to avoid circular includes between
52 // this header file and thread.hpp.
53 static bool current_thread_in_native();
54
55 public:
56 // Low tag bit in jobject used to distinguish a jweak. jweak is
57 // type equivalent to jobject, but there are places where we need to
58 // be able to distinguish jweak values from other jobjects, and
59 // is_weak_global_handle is unsuitable for performance reasons. To
60 // provide such a test we add weak_tag_value to the (aligned) byte
61 // address designated by the jobject to produce the corresponding
62 // jweak. Accessing the value of a jobject must account for it
63 // being a possibly offset jweak.
64 static const uintptr_t weak_tag_size = 1;
65 static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
66 static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
67 static const int weak_tag_value = 1;
68
69 // Resolve handle into oop
70 inline static oop resolve(jobject handle);
71 // Resolve externally provided handle into oop with some guards
72 inline static oop resolve_external_guard(jobject handle);
73 // Resolve handle into oop, result guaranteed not to be null
74 inline static oop resolve_non_null(jobject handle);
75
76 // Local handles
77 static jobject make_local(oop obj);
78 static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known
79 static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
80 inline static void destroy_local(jobject handle);
81
82 // Global handles
83 static jobject make_global(Handle obj);
84 static void destroy_global(jobject handle);
85
86 // Weak global handles
87 static jobject make_weak_global(Handle obj);
88 static void destroy_weak_global(jobject handle);
89 static bool is_global_weak_cleared(jweak handle); // Test jweak without resolution
90
91 // Sentinel marking deleted handles in block. Note that we cannot store NULL as
92 // the sentinel, since clearing weak global JNI refs are done by storing NULL in
93 // the handle. The handle may not be reused before destroy_weak_global is called.
94 static oop deleted_handle() { return _deleted_handle; }
95
96 // Initialization
97 static void initialize();
98
99 // Debugging
100 static void print_on(outputStream* st);
101 static void print() { print_on(tty); }
102 static void verify();
103 static bool is_local_handle(Thread* thread, jobject handle);
104 static bool is_frame_handle(JavaThread* thr, jobject obj);
105 static bool is_global_handle(jobject handle);
106 static bool is_weak_global_handle(jobject handle);
107 static long global_handle_memory_usage();
108 static long weak_global_handle_memory_usage();
109
110 // Garbage collection support(global handles only, local handles are traversed from thread)
111 // Traversal of regular global handles
112 static void oops_do(OopClosure* f);
113 // Traversal of weak global handles. Unreachable oops are cleared.
114 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
115 // Traversal of weak global handles.
116 static void weak_oops_do(OopClosure* f);
117 };
118
119
120
121 // JNI handle blocks holding local/global JNI handles
122
123 class JNIHandleBlock : public CHeapObj<mtInternal> {
124 friend class VMStructs;
125 friend class CppInterpreter;
126
127 private:
128 enum SomeConstants {
129 block_size_in_oops = 32 // Number of handles per handle block
130 };
131
132 oop _handles[block_size_in_oops]; // The handles
133 int _top; // Index of next unused handle
134 JNIHandleBlock* _next; // Link to next block
135
136 // The following instance variables are only used by the first block in a chain.
137 // Having two types of blocks complicates the code and the space overhead in negligible.
138 JNIHandleBlock* _last; // Last block in use
139 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
140 oop* _free_list; // Handle free list
141 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
142
143 // Check JNI, "planned capacity" for current frame (or push/ensure)
144 size_t _planned_capacity;
145
146 #ifndef PRODUCT
147 JNIHandleBlock* _block_list_link; // Link for list below
148 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only)
149 #endif
150
151 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks
152 static int _blocks_allocated; // For debugging/printing
153
154 // Fill block with bad_handle values
155 void zap() NOT_DEBUG_RETURN;
156
157 // Free list computation
158 void rebuild_free_list();
159
160 // No more handles in the both the current and following blocks
161 void clear() { _top = 0; }
162
163 public:
164 // Handle allocation
165 jobject allocate_handle(oop obj);
166
167 // Release Handle
168 void release_handle(jobject);
169
170 // Block allocation and block free list management
171 static JNIHandleBlock* allocate_block(Thread* thread = NULL);
172 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
173
174 // JNI PushLocalFrame/PopLocalFrame support
175 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
176 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
177
178 // Stub generator support
179 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
180
181 // Garbage collection support
182 // Traversal of regular handles
183 void oops_do(OopClosure* f);
184 // Traversal of weak handles. Unreachable oops are cleared.
185 void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
186
187 // Checked JNI support
188 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
189 const size_t get_planned_capacity() { return _planned_capacity; }
190 const size_t get_number_of_live_handles();
191
192 // Debugging
193 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
194 bool contains(jobject handle) const; // Does this block contain handle
195 int length() const; // Length of chain starting with this block
196 long memory_usage() const;
197 #ifndef PRODUCT
198 static bool any_contains(jobject handle); // Does any block currently in use contain handle
199 static void print_statistics();
200 #endif
201 };
202
203 inline bool JNIHandles::is_jweak(jobject handle) {
204 STATIC_ASSERT(weak_tag_size == 1);
205 STATIC_ASSERT(weak_tag_value == 1);
206 return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
207 }
208
209 inline oop& JNIHandles::jobject_ref(jobject handle) {
210 assert(!is_jweak(handle), "precondition");
211 return *reinterpret_cast<oop*>(handle);
212 }
213
214 inline oop& JNIHandles::jweak_ref(jobject handle) {
215 assert(is_jweak(handle), "precondition");
216 char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;
217 return *reinterpret_cast<oop*>(ptr);
218 }
219
220 // external_guard is true if called from resolve_external_guard.
221 // Treat deleted (and possibly zapped) as NULL for external_guard,
222 // else as (asserted) error.
223 template<bool external_guard>
224 inline oop JNIHandles::guard_value(oop value) {
225 if (!external_guard) {
226 assert(value != deleted_handle(), "Used a deleted global handle");
227 } else if (value == deleted_handle()) {
228 value = NULL;
229 }
230 return value;
231 }
232
233 // external_guard is true if called from resolve_external_guard.
234 template<bool external_guard>
235 inline oop JNIHandles::resolve_impl(jobject handle) {
236 assert(handle != NULL, "precondition");
237 assert(!current_thread_in_native(), "must not be in native");
238 oop result;
239 if (is_jweak(handle)) { // Unlikely
240 result = resolve_jweak<external_guard>(handle);
241 } else {
242 result = jobject_ref(handle);
243 // Construction of jobjects canonicalize a null value into a null
244 // jobject, so for non-jweak the pointee should never be null.
245 assert(external_guard || result != NULL,
246 "Invalid value read from jni handle");
247 result = guard_value<external_guard>(result);
248 }
249 return result;
250 }
251
252 inline oop JNIHandles::resolve(jobject handle) {
253 oop result = NULL;
254 if (handle != NULL) {
255 result = resolve_impl<false /* external_guard */ >(handle);
256 }
257 return result;
258 }
259
260 // Resolve some erroneous cases to NULL, rather than treating them as
261 // possibly unchecked errors. In particular, deleted handles are
262 // treated as NULL (though a deleted and later reallocated handle
263 // isn't detected).
264 inline oop JNIHandles::resolve_external_guard(jobject handle) {
265 oop result = NULL;
266 if (handle != NULL) {
267 result = resolve_impl<true /* external_guard */ >(handle);
268 }
269 return result;
270 }
271
272 inline oop JNIHandles::resolve_non_null(jobject handle) {
273 assert(handle != NULL, "JNI handle should not be null");
274 oop result = resolve_impl<false /* external_guard */ >(handle);
275 assert(result != NULL, "NULL read from jni handle");
276 return result;
277 }
278
279 inline void JNIHandles::destroy_local(jobject handle) {
280 if (handle != NULL) {
281 jobject_ref(handle) = deleted_handle();
282 }
283 }
284
285 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP