1 /*
2 * Copyright (c) 1998, 2018, 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 class OopStorage;
33
34
35 // Interface for creating and resolving local/global JNI handles
36
37 class JNIHandles : AllStatic {
38 friend class VMStructs;
39 private:
40 static OopStorage* _global_handles;
41 static OopStorage* _weak_global_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 resolve_impl(jobject handle);
48 static oop resolve_jweak(jweak handle);
49
50 // This method is not inlined in order to avoid circular includes between
51 // this header file and thread.hpp.
52 static bool current_thread_in_native();
53
54 public:
55 // Low tag bit in jobject used to distinguish a jweak. jweak is
56 // type equivalent to jobject, but there are places where we need to
57 // be able to distinguish jweak values from other jobjects, and
58 // is_weak_global_handle is unsuitable for performance reasons. To
59 // provide such a test we add weak_tag_value to the (aligned) byte
60 // address designated by the jobject to produce the corresponding
61 // jweak. Accessing the value of a jobject must account for it
62 // being a possibly offset jweak.
63 static const uintptr_t weak_tag_size = 1;
64 static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
65 static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
66 static const int weak_tag_value = 1;
67
68 // Resolve handle into oop
69 inline static oop resolve(jobject handle);
70 // Resolve handle into oop, result guaranteed not to be null
71 inline static oop resolve_non_null(jobject handle);
72 // Resolve externally provided handle into oop with some guards
73 static oop resolve_external_guard(jobject handle);
74
75 // Local handles
76 static jobject make_local(oop obj);
77 static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known
78 static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
79 inline static void destroy_local(jobject handle);
80
81 // Global handles
82 static jobject make_global(Handle obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
83 static void destroy_global(jobject handle);
84
85 // Weak global handles
86 static jobject make_weak_global(Handle obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
87 static void destroy_weak_global(jobject handle);
88 static bool is_global_weak_cleared(jweak handle); // Test jweak without resolution
89
90 // Initialization
91 static void initialize();
92
93 // Debugging
94 static void print_on(outputStream* st);
95 static void print() { print_on(tty); }
96 static void verify();
97 // The category predicates all require handle != NULL.
98 static bool is_local_handle(Thread* thread, jobject handle);
99 static bool is_frame_handle(JavaThread* thread, jobject handle);
100 static bool is_global_handle(jobject handle);
101 static bool is_weak_global_handle(jobject handle);
102 static size_t global_handle_memory_usage();
103 static size_t weak_global_handle_memory_usage();
104
105 #ifndef PRODUCT
106 // Is handle from any local block of any thread?
107 static bool is_local_handle(jobject handle);
108 #endif
109
110 // precondition: handle != NULL.
111 static jobjectRefType handle_type(Thread* thread, jobject handle);
112
113 // Garbage collection support(global handles only, local handles are traversed from thread)
114 // Traversal of regular global handles
115 static void oops_do(OopClosure* f);
116 // Traversal of weak global handles. Unreachable oops are cleared.
117 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
118 // Traversal of weak global handles.
119 static void weak_oops_do(OopClosure* f);
120 };
121
122
123
124 // JNI handle blocks holding local/global JNI handles
125
126 class JNIHandleBlock : public CHeapObj<mtInternal> {
127 friend class VMStructs;
128 friend class CppInterpreter;
129
130 private:
131 enum SomeConstants {
132 block_size_in_oops = 32 // Number of handles per handle block
133 };
134
135 oop _handles[block_size_in_oops]; // The handles
136 int _top; // Index of next unused handle
137 JNIHandleBlock* _next; // Link to next block
138
139 // The following instance variables are only used by the first block in a chain.
140 // Having two types of blocks complicates the code and the space overhead in negligible.
141 JNIHandleBlock* _last; // Last block in use
142 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
143 oop* _free_list; // Handle free list
144 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
145
146 // Check JNI, "planned capacity" for current frame (or push/ensure)
147 size_t _planned_capacity;
148
149 #ifndef PRODUCT
150 JNIHandleBlock* _block_list_link; // Link for list below
151 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only)
152 #endif
153
154 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks
155 static int _blocks_allocated; // For debugging/printing
156
157 // Fill block with bad_handle values
158 void zap() NOT_DEBUG_RETURN;
159
160 // Free list computation
161 void rebuild_free_list();
162
163 // No more handles in the both the current and following blocks
164 void clear() { _top = 0; }
165
166 public:
167 // Handle allocation
168 jobject allocate_handle(oop obj);
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 handles
183 void oops_do(OopClosure* f);
184
185 // Checked JNI support
186 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
187 const size_t get_planned_capacity() { return _planned_capacity; }
188 const size_t get_number_of_live_handles();
189
190 // Debugging
191 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
192 bool contains(jobject handle) const; // Does this block contain handle
193 size_t length() const; // Length of chain starting with this block
194 size_t memory_usage() const;
195 #ifndef PRODUCT
196 static bool any_contains(jobject handle); // Does any block currently in use contain handle
197 static void print_statistics();
198 #endif
199 };
200
201 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP