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