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);
186 const size_t get_planned_capacity() { return _planned_capacity; }
187 const size_t get_number_of_live_handles();
188
189 // Debugging
190 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
191 bool contains(jobject handle) const; // Does this block contain handle
192 int length() const; // Length of chain starting with this block
193 long memory_usage() const;
194 #ifndef PRODUCT
195 static bool any_contains(jobject handle); // Does any block currently in use contain handle
196 static void print_statistics();
197 #endif
198 };
199
200 inline bool JNIHandles::is_jweak(jobject handle) {
201 STATIC_ASSERT(weak_tag_size == 1);
202 STATIC_ASSERT(weak_tag_value == 1);
203 return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
204 }
205
206 inline oop& JNIHandles::jobject_ref(jobject handle) {
207 assert(!is_jweak(handle), "precondition");
208 return *reinterpret_cast<oop*>(handle);
209 }
210
211 inline oop& JNIHandles::jweak_ref(jobject handle) {
212 assert(is_jweak(handle), "precondition");
213 char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;
214 return *reinterpret_cast<oop*>(ptr);
215 }
216
217 // external_guard is true if called from resolve_external_guard.
218 // Treat deleted (and possibly zapped) as NULL for external_guard,
219 // else as (asserted) error.
220 template<bool external_guard>
221 inline oop JNIHandles::guard_value(oop value) {
222 if (!external_guard) {
223 assert(value != badJNIHandle, "Pointing to zapped jni handle area");
224 assert(value != deleted_handle(), "Used a deleted global handle");
225 } else if ((value == badJNIHandle) || (value == deleted_handle())) {
226 value = NULL;
227 }
228 return value;
229 }
230
231 // external_guard is true if called from resolve_external_guard.
232 template<bool external_guard>
233 inline oop JNIHandles::resolve_impl(jobject handle) {
234 assert(handle != NULL, "precondition");
235 oop result;
236 if (is_jweak(handle)) { // Unlikely
237 result = resolve_jweak<external_guard>(handle);
238 } else {
239 result = jobject_ref(handle);
240 // Construction of jobjects canonicalize a null value into a null
241 // jobject, so for non-jweak the pointee should never be null.
242 assert(external_guard || result != NULL,
243 "Invalid value read from jni handle");
244 result = guard_value<external_guard>(result);
245 }
246 return result;
247 }
248
249 inline oop JNIHandles::resolve(jobject handle) {
250 oop result = NULL;
251 if (handle != NULL) {
252 result = resolve_impl<false /* external_guard */ >(handle);
253 }
254 return result;
255 }
256
257 // Resolve some erroneous cases to NULL, rather than treating them as
258 // possibly unchecked errors. In particular, deleted handles are
259 // treated as NULL (though a deleted and later reallocated handle
260 // isn't detected).
261 inline oop JNIHandles::resolve_external_guard(jobject handle) {
262 oop result = NULL;
263 if (handle != NULL) {
264 result = resolve_impl<true /* external_guard */ >(handle);
265 }
266 return result;
267 }
268
269 inline oop JNIHandles::resolve_non_null(jobject handle) {
270 assert(handle != NULL, "JNI handle should not be null");
271 oop result = resolve_impl<false /* external_guard */ >(handle);
272 assert(result != NULL, "NULL read from jni handle");
273 return result;
274 }
275
276 inline void JNIHandles::destroy_local(jobject handle) {
277 if (handle != NULL) {
278 jobject_ref(handle) = deleted_handle();
279 }
280 }
281
282 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP
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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 oop* oop_addr(jobject handle);
44 inline static bool is_jweak(jobject handle);
45
46 template<bool external_guard> inline static oop guard_value(oop value);
47 template<bool external_guard> inline static oop resolve_impl(jobject handle);
48 template<bool external_guard> static oop resolve_jweak(jweak handle);
49
50 static oop resolve_handle(jobject handle);
51
52 enum ResolveType {
53 DEFAULT,
54 EXTERNAL_GUARD,
55 NOT_NULL
56 };
57
58 template <ResolveType type>
59 class JNIHandleResolver: public StackObj {
60 oop _value;
61
62 bool is_not_null() const {
63 return type == NOT_NULL;
64 }
65
66 bool is_external_guard() const {
67 return type == EXTERNAL_GUARD;
68 }
69
70 bool is_default() const {
71 return type == DEFAULT;
72 }
73
74 bool is_dead(oop value) const {
75 return value == NULL || value == badJNIHandle || value == deleted_handle();
76 }
77
78 void assert_not_dead(oop value) const {
79 if (!is_external_guard()) {
80 assert(value != badJNIHandle, "Pointing to zapped jni handle area");
81 assert(value == NULL || value != deleted_handle(), "Used a deleted global handle");
82 }
83 }
84
85 public:
86 JNIHandleResolver(jobject handle) {
87 oop value;
88 assert(!is_not_null() || handle != NULL, "JNI handle should not be null");
89 if (!is_not_null() && handle == NULL) {
90 value = NULL;
91 } else {
92 value = *oop_addr(handle);
93 assert_not_dead(value);
94 if (is_external_guard() && is_dead(value)) {
95 value = NULL;
96 } else {
97 value = resolve_handle(handle);
98 }
99 }
100 _value = value;
101 }
102
103 oop value() const {
104 return _value;
105 }
106
107 ~JNIHandleResolver() {
108 assert_not_dead(_value);
109 assert(!is_not_null() || _value != NULL, "NULL read from jni handle");
110 }
111 };
112
113 public:
114 // Low tag bit in jobject used to distinguish a jweak. jweak is
115 // type equivalent to jobject, but there are places where we need to
116 // be able to distinguish jweak values from other jobjects, and
117 // is_weak_global_handle is unsuitable for performance reasons. To
118 // provide such a test we add weak_tag_value to the (aligned) byte
119 // address designated by the jobject to produce the corresponding
120 // jweak. Accessing the value of a jobject must account for it
121 // being a possibly offset jweak.
122 static const uintptr_t weak_tag_size = 1;
123 static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
124 static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
125 static const int weak_tag_value = 1;
126
127 // Resolve handle into oop
128 inline static oop resolve(jobject handle);
129 // Resolve externally provided handle into oop with some guards
130 inline static oop resolve_external_guard(jobject handle);
131 // Resolve handle into oop, result guaranteed not to be null
132 inline static oop resolve_non_null(jobject handle);
248 const size_t get_planned_capacity() { return _planned_capacity; }
249 const size_t get_number_of_live_handles();
250
251 // Debugging
252 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
253 bool contains(jobject handle) const; // Does this block contain handle
254 int length() const; // Length of chain starting with this block
255 long memory_usage() const;
256 #ifndef PRODUCT
257 static bool any_contains(jobject handle); // Does any block currently in use contain handle
258 static void print_statistics();
259 #endif
260 };
261
262 inline bool JNIHandles::is_jweak(jobject handle) {
263 STATIC_ASSERT(weak_tag_size == 1);
264 STATIC_ASSERT(weak_tag_value == 1);
265 return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
266 }
267
268 inline oop* JNIHandles::oop_addr(jobject handle) {
269 return (oop*)(reinterpret_cast<uintptr_t>(handle) & ~(weak_tag_mask));
270 }
271
272 inline oop JNIHandles::resolve(jobject handle) {
273 return JNIHandleResolver<DEFAULT>(handle).value();
274 }
275
276 // Resolve some erroneous cases to NULL, rather than treating them as
277 // possibly unchecked errors. In particular, deleted handles are
278 // treated as NULL (though a deleted and later reallocated handle
279 // isn't detected).
280 inline oop JNIHandles::resolve_external_guard(jobject handle) {
281 return JNIHandleResolver<EXTERNAL_GUARD>(handle).value();
282 }
283
284 inline oop JNIHandles::resolve_non_null(jobject handle) {
285 return JNIHandleResolver<NOT_NULL>(handle).value();
286 }
287
288 inline void JNIHandles::destroy_local(jobject handle) {
289 if (handle != NULL) {
290 *oop_addr(handle) = deleted_handle();
291 }
292 }
293
294 #endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP
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