1 /*
2 * Copyright (c) 1998, 2020, 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_RUNTIME_JNIHANDLES_HPP
26 #define SHARE_RUNTIME_JNIHANDLES_HPP
27
28 #include "memory/allocation.hpp"
29 #include "runtime/handles.hpp"
30
31 class JavaThread;
32 class OopStorage;
33 class Thread;
34
35 // Interface for creating and resolving local/global JNI handles
36
37 class JNIHandles : AllStatic {
38 friend class VMStructs;
39 private:
40 // These are used by the serviceability agent.
41 static OopStorage* _global_handles;
42 static OopStorage* _weak_global_handles;
43 friend void jni_handles_init();
44
45 static OopStorage* global_handles();
46 static OopStorage* weak_global_handles();
47
48 inline static bool is_jweak(jobject handle);
49 inline static oop* jobject_ptr(jobject handle); // NOT jweak!
50 inline static oop* jweak_ptr(jobject handle);
51
52 template <DecoratorSet decorators, bool external_guard> inline static oop resolve_impl(jobject handle);
53
54 // Resolve handle into oop, without keeping the object alive
55 inline static oop resolve_no_keepalive(jobject handle);
56
57 // This method is not inlined in order to avoid circular includes between
58 // this header file and thread.hpp.
59 static bool current_thread_in_native();
60
61 public:
62 // Low tag bit in jobject used to distinguish a jweak. jweak is
63 // type equivalent to jobject, but there are places where we need to
64 // be able to distinguish jweak values from other jobjects, and
65 // is_weak_global_handle is unsuitable for performance reasons. To
66 // provide such a test we add weak_tag_value to the (aligned) byte
67 // address designated by the jobject to produce the corresponding
68 // jweak. Accessing the value of a jobject must account for it
69 // being a possibly offset jweak.
70 static const uintptr_t weak_tag_size = 1;
71 static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
72 static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
73 static const int weak_tag_value = 1;
74
75 // Resolve handle into oop
76 inline static oop resolve(jobject handle);
77 // Resolve handle into oop, result guaranteed not to be null
78 inline static oop resolve_non_null(jobject handle);
79 // Resolve externally provided handle into oop with some guards
80 static oop resolve_external_guard(jobject handle);
81
82 // Check for equality without keeping objects alive
83 static bool is_same_object(jobject handle1, jobject handle2);
84
85 // Local handles
86 static jobject make_local(oop obj);
87 static jobject make_local(Thread* thread, oop obj, // Faster version when current thread is known
88 AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
89 inline static void destroy_local(jobject handle);
90
91 // Global handles
92 static jobject make_global(Handle obj,
93 AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
94 static void destroy_global(jobject handle);
95
96 // Weak global handles
97 static jobject make_weak_global(Handle obj,
98 AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
99 static void destroy_weak_global(jobject handle);
100 static bool is_global_weak_cleared(jweak handle); // Test jweak without resolution
101
102 // Initialization
103 static void initialize();
104
105 // Debugging
106 static void print_on(outputStream* st);
107 static void print();
108 static void verify();
109 // The category predicates all require handle != NULL.
110 static bool is_local_handle(Thread* thread, jobject handle);
111 static bool is_frame_handle(JavaThread* thread, jobject handle);
112 static bool is_global_handle(jobject handle);
113 static bool is_weak_global_handle(jobject handle);
114 static size_t global_handle_memory_usage();
115 static size_t weak_global_handle_memory_usage();
116
117 #ifndef PRODUCT
118 // Is handle from any local block of any thread?
119 static bool is_local_handle(jobject handle);
120 #endif
121
122 // precondition: handle != NULL.
123 static jobjectRefType handle_type(Thread* thread, jobject handle);
124
125 // Garbage collection support(global handles only, local handles are traversed from thread)
126 // Traversal of regular global handles
127 static void oops_do(OopClosure* f);
128 // Traversal of weak global handles. Unreachable oops are cleared.
129 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
130 // Traversal of weak global handles.
131 static void weak_oops_do(OopClosure* f);
132
133 static bool is_global_storage(const OopStorage* storage);
134 };
135
136
137
138 // JNI handle blocks holding local/global JNI handles
139
140 class JNIHandleBlock : public CHeapObj<mtInternal> {
141 friend class VMStructs;
142 friend class ZeroInterpreter;
143
144 private:
145 enum SomeConstants {
146 block_size_in_oops = 32 // Number of handles per handle block
147 };
148
149 uintptr_t _handles[block_size_in_oops]; // The handles
150 int _top; // Index of next unused handle
151 JNIHandleBlock* _next; // Link to next block
152
153 // The following instance variables are only used by the first block in a chain.
154 // Having two types of blocks complicates the code and the space overhead in negligible.
155 JNIHandleBlock* _last; // Last block in use
156 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
157 uintptr_t* _free_list; // Handle free list
158 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
159
160 // Check JNI, "planned capacity" for current frame (or push/ensure)
161 size_t _planned_capacity;
162
163 #ifndef PRODUCT
164 JNIHandleBlock* _block_list_link; // Link for list below
165 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only)
166 #endif
167
168 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks
169 static int _blocks_allocated; // For debugging/printing
170
171 // Fill block with bad_handle values
172 void zap() NOT_DEBUG_RETURN;
173
174 // Free list computation
175 void rebuild_free_list();
176
177 // No more handles in the both the current and following blocks
178 void clear() { _top = 0; }
179
180 public:
181 // Handle allocation
182 jobject allocate_handle(oop obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
183
184 // Block allocation and block free list management
185 static JNIHandleBlock* allocate_block(Thread* thread = NULL, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
186 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
187
188 // JNI PushLocalFrame/PopLocalFrame support
189 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
190 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
191
192 // Stub generator support
193 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
194
195 // Garbage collection support
196 // Traversal of handles
197 void oops_do(OopClosure* f);
198
199 // Checked JNI support
200 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
201 const size_t get_planned_capacity() { return _planned_capacity; }
202 const size_t get_number_of_live_handles();
203
204 // Debugging
205 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
206 bool contains(jobject handle) const; // Does this block contain handle
207 size_t length() const; // Length of chain starting with this block
208 size_t memory_usage() const;
209 #ifndef PRODUCT
210 static bool any_contains(jobject handle); // Does any block currently in use contain handle
211 static void print_statistics();
212 #endif
213 };
214
215 #endif // SHARE_RUNTIME_JNIHANDLES_HPP