1/*
2 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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12 * version 2 for more details (a copy is included in the LICENSE file that
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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
31class JavaThread;
32class OopStorage;
33class Thread;
34
35// Interface for creating and resolving local/global JNI handles
36
37class 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_ptr(jobject handle); // NOT jweak!
45 inline static oop* jweak_ptr(jobject handle);
46
47 template <DecoratorSet decorators, bool external_guard> inline static oop resolve_impl(jobject handle);
48
49 // Resolve handle into oop, without keeping the object alive
50 inline static oop resolve_no_keepalive(jobject handle);
51
52 // This method is not inlined in order to avoid circular includes between
53 // this header file and thread.hpp.
54 static bool current_thread_in_native();
55
56 public:
57 // Low tag bit in jobject used to distinguish a jweak. jweak is
58 // type equivalent to jobject, but there are places where we need to
59 // be able to distinguish jweak values from other jobjects, and
60 // is_weak_global_handle is unsuitable for performance reasons. To
61 // provide such a test we add weak_tag_value to the (aligned) byte
62 // address designated by the jobject to produce the corresponding
63 // jweak. Accessing the value of a jobject must account for it
64 // being a possibly offset jweak.
65 static const uintptr_t weak_tag_size = 1;
66 static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
67 static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
68 static const int weak_tag_value = 1;
69
70 // Resolve handle into oop
71 inline static oop resolve(jobject handle);
72 // Resolve handle into oop, result guaranteed not to be null
73 inline static oop resolve_non_null(jobject handle);
74 // Resolve externally provided handle into oop with some guards
75 static oop resolve_external_guard(jobject handle);
76
77 // Check for equality without keeping objects alive
78 static bool is_same_object(jobject handle1, jobject handle2);
79
80 // Local handles
81 static jobject make_local(oop obj);
82 static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known
83 static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
84 inline static void destroy_local(jobject handle);
85
86 // Global handles
87 static jobject make_global(Handle obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
88 static void destroy_global(jobject handle);
89
90 // Weak global handles
91 static jobject make_weak_global(Handle obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
92 static void destroy_weak_global(jobject handle);
93 static bool is_global_weak_cleared(jweak handle); // Test jweak without resolution
94
95 // Initialization
96 static void initialize();
97
98 // Debugging
99 static void print_on(outputStream* st);
100 static void print();
101 static void verify();
102 // The category predicates all require handle != NULL.
103 static bool is_local_handle(Thread* thread, jobject handle);
104 static bool is_frame_handle(JavaThread* thread, jobject handle);
105 static bool is_global_handle(jobject handle);
106 static bool is_weak_global_handle(jobject handle);
107 static size_t global_handle_memory_usage();
108 static size_t weak_global_handle_memory_usage();
109
110#ifndef PRODUCT
111 // Is handle from any local block of any thread?
112 static bool is_local_handle(jobject handle);
113#endif
114
115 // precondition: handle != NULL.
116 static jobjectRefType handle_type(Thread* thread, jobject handle);
117
118 // Garbage collection support(global handles only, local handles are traversed from thread)
119 // Traversal of regular global handles
120 static void oops_do(OopClosure* f);
121 // Traversal of weak global handles. Unreachable oops are cleared.
122 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
123 // Traversal of weak global handles.
124 static void weak_oops_do(OopClosure* f);
125
126 static OopStorage* global_handles();
127 static OopStorage* weak_global_handles();
128};
129
130
131
132// JNI handle blocks holding local/global JNI handles
133
134class JNIHandleBlock : public CHeapObj<mtInternal> {
135 friend class VMStructs;
136 friend class CppInterpreter;
137
138 private:
139 enum SomeConstants {
140 block_size_in_oops = 32 // Number of handles per handle block
141 };
142
143 oop _handles[block_size_in_oops]; // The handles
144 int _top; // Index of next unused handle
145 JNIHandleBlock* _next; // Link to next block
146
147 // The following instance variables are only used by the first block in a chain.
148 // Having two types of blocks complicates the code and the space overhead in negligible.
149 JNIHandleBlock* _last; // Last block in use
150 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
151 oop* _free_list; // Handle free list
152 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
153
154 // Check JNI, "planned capacity" for current frame (or push/ensure)
155 size_t _planned_capacity;
156
157 #ifndef PRODUCT
158 JNIHandleBlock* _block_list_link; // Link for list below
159 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only)
160 #endif
161
162 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks
163 static int _blocks_allocated; // For debugging/printing
164
165 // Fill block with bad_handle values
166 void zap() NOT_DEBUG_RETURN;
167
168 // Free list computation
169 void rebuild_free_list();
170
171 // No more handles in the both the current and following blocks
172 void clear() { _top = 0; }
173
174 public:
175 // Handle allocation
176 jobject allocate_handle(oop obj);
177
178 // Block allocation and block free list management
179 static JNIHandleBlock* allocate_block(Thread* thread = NULL);
180 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
181
182 // JNI PushLocalFrame/PopLocalFrame support
183 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
184 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
185
186 // Stub generator support
187 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
188
189 // Garbage collection support
190 // Traversal of handles
191 void oops_do(OopClosure* f);
192
193 // Checked JNI support
194 void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
195 const size_t get_planned_capacity() { return _planned_capacity; }
196 const size_t get_number_of_live_handles();
197
198 // Debugging
199 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
200 bool contains(jobject handle) const; // Does this block contain handle
201 size_t length() const; // Length of chain starting with this block
202 size_t memory_usage() const;
203 #ifndef PRODUCT
204 static bool any_contains(jobject handle); // Does any block currently in use contain handle
205 static void print_statistics();
206 #endif
207};
208
209#endif // SHARE_RUNTIME_JNIHANDLES_HPP
210