1 /*
2 * Copyright (c) 1998, 2014, 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 "runtime/handles.hpp"
29 #include "utilities/top.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 public:
44 // Resolve handle into oop
45 inline static oop resolve(jobject handle);
46 // Resolve externally provided handle into oop with some guards
47 inline static oop resolve_external_guard(jobject handle);
48 // Resolve handle into oop, result guaranteed not to be null
49 inline static oop resolve_non_null(jobject handle);
50
51 // Local handles
52 static jobject make_local(oop obj);
53 static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known
54 static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
55 inline static void destroy_local(jobject handle);
56
57 // Global handles
58 static jobject make_global(Handle obj);
59 static void destroy_global(jobject handle);
60
61 // Weak global handles
62 static jobject make_weak_global(Handle obj);
63 static void destroy_weak_global(jobject handle);
64
65 // Sentinel marking deleted handles in block. Note that we cannot store NULL as
66 // the sentinel, since clearing weak global JNI refs are done by storing NULL in
67 // the handle. The handle may not be reused before destroy_weak_global is called.
68 static oop deleted_handle() { return _deleted_handle; }
69
70 // Initialization
71 static void initialize();
72
73 // Debugging
74 static void print_on(outputStream* st);
75 static void print() { print_on(tty); }
76 static void verify();
77 static bool is_local_handle(Thread* thread, jobject handle);
78 static bool is_frame_handle(JavaThread* thr, jobject obj);
79 static bool is_global_handle(jobject handle);
80 static bool is_weak_global_handle(jobject handle);
81 static long global_handle_memory_usage();
82 static long weak_global_handle_memory_usage();
83
84 // Garbage collection support(global handles only, local handles are traversed from thread)
85 // Traversal of regular global handles
86 static void oops_do(OopClosure* f);
87 // Traversal of weak global handles. Unreachable oops are cleared.
88 static size_t weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
89 };
90
91
92
93 // JNI handle blocks holding local/global JNI handles
94
95 class JNIHandleBlock : public CHeapObj<mtInternal> {
96 friend class VMStructs;
97 friend class CppInterpreter;
98
99 private:
100 enum SomeConstants {
101 block_size_in_oops = 32 // Number of handles per handle block
102 };
103
104 oop _handles[block_size_in_oops]; // The handles
105 int _top; // Index of next unused handle
106 JNIHandleBlock* _next; // Link to next block
107
108 // The following instance variables are only used by the first block in a chain.
109 // Having two types of blocks complicates the code and the space overhead in negligible.
110 JNIHandleBlock* _last; // Last block in use
111 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
112 oop* _free_list; // Handle free list
113 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
114
115 // Check JNI, "planned capacity" for current frame (or push/ensure)
116 size_t _planned_capacity;
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 protected:
130 // No more handles in the both the current and following blocks
131 void clear() { _top = 0; }
132
133 private:
134 // Free list computation
135 void rebuild_free_list();
136
137 public:
138 // Handle allocation
139 jobject allocate_handle(oop obj);
140
141 // Block allocation and block free list management
142 static JNIHandleBlock* allocate_block(Thread* thread = NULL);
143 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
144
145 // JNI PushLocalFrame/PopLocalFrame support
146 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
147 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
148
149 // Stub generator support
150 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
151
152 // Garbage collection support
153 // Traversal of regular handles
154 void oops_do(OopClosure* f);
155 // Traversal of weak handles. Unreachable oops are cleared.
156 size_t weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
157
158 // Checked JNI support
159 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
160 const size_t get_planned_capacity() { return _planned_capacity; }
161 const size_t get_number_of_live_handles();
162
163 // Debugging
164 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
165 bool contains(jobject handle) const; // Does this block contain handle
166 int length() const; // Length of chain starting with this block
167 long memory_usage() const;
168 #ifndef PRODUCT
169 static bool any_contains(jobject handle); // Does any block currently in use contain handle
170 static void print_statistics();
171 #endif
172 };
173
174
175 inline oop JNIHandles::resolve(jobject handle) {
176 oop result = (handle == NULL ? (oop)NULL : *(oop*)handle);
177 assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle");
178 assert(result != badJNIHandle, "Pointing to zapped jni handle area");
179 return result;
180 };
181
182
183 inline oop JNIHandles::resolve_external_guard(jobject handle) {
184 if (handle == NULL) return NULL;
185 oop result = *(oop*)handle;
186 if (result == NULL || result == badJNIHandle) return NULL;
187 return result;
188 };
189
190
191 inline oop JNIHandles::resolve_non_null(jobject handle) {
192 assert(handle != NULL, "JNI handle should not be null");
193 oop result = *(oop*)handle;
194 assert(result != NULL, "Invalid value read from jni handle");
195 assert(result != badJNIHandle, "Pointing to zapped jni handle area");
196 // Don't let that private _deleted_handle object escape into the wild.
197 assert(result != deleted_handle(), "Used a deleted global handle.");
198 return result;
199 };
200
201 inline void JNIHandles::destroy_local(jobject handle) {
202 if (handle != NULL) {
203 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
204 }
205 }
206
207 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP