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1 /*
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2 * Copyright 1998-2007 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 class JNIHandleBlock;
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26
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27
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28 // Interface for creating and resolving local/global JNI handles
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29
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30 class JNIHandles : AllStatic {
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31 friend class VMStructs;
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32 private:
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33 static JNIHandleBlock* _global_handles; // First global handle block
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34 static JNIHandleBlock* _weak_global_handles; // First weak global handle block
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35 static oop _deleted_handle; // Sentinel marking deleted handles
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36
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37 public:
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38 // Resolve handle into oop
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39 inline static oop resolve(jobject handle);
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40 // Resolve externally provided handle into oop with some guards
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41 inline static oop resolve_external_guard(jobject handle);
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42 // Resolve handle into oop, result guaranteed not to be null
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43 inline static oop resolve_non_null(jobject handle);
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44
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45 // Local handles
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46 static jobject make_local(oop obj);
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47 static jobject make_local(JNIEnv* env, oop obj); // Fast version when env is known
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48 static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
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49 inline static void destroy_local(jobject handle);
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50
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51 // Global handles
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52 static jobject make_global(Handle obj);
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53 static void destroy_global(jobject handle);
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54
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55 // Weak global handles
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56 static jobject make_weak_global(Handle obj);
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57 static void destroy_weak_global(jobject handle);
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58
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59 // jmethodID handling (as Weak global handles).
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60 // Because the useful life-span of a jmethodID cannot be determined, once created they are
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61 // never reclaimed. The methods to which they refer, however, can be GC'ed away if the class
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62 // is unloaded or if the method is made obsolete or deleted -- in these cases, the jmethodID
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63 // refers to NULL (as is the case for any weak reference).
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64 static jmethodID make_jmethod_id(methodHandle mh);
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65 static void destroy_jmethod_id(jmethodID mid);
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66 inline static methodOop resolve_jmethod_id(jmethodID mid);
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67 inline static methodOop checked_resolve_jmethod_id(jmethodID mid); // NULL on invalid jmethodID
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68 static void change_method_associated_with_jmethod_id(jmethodID jmid, methodHandle mh);
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69
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70 // Sentinel marking deleted handles in block. Note that we cannot store NULL as
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71 // the sentinel, since clearing weak global JNI refs are done by storing NULL in
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72 // the handle. The handle may not be reused before destroy_weak_global is called.
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73 static oop deleted_handle() { return _deleted_handle; }
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74
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75 // Initialization
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76 static void initialize();
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77
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78 // Debugging
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79 static void print_on(outputStream* st);
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80 static void print() { print_on(tty); }
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81 static void verify();
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82 static bool is_local_handle(Thread* thread, jobject handle);
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83 static bool is_frame_handle(JavaThread* thr, jobject obj);
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84 static bool is_global_handle(jobject handle);
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85 static bool is_weak_global_handle(jobject handle);
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86 static long global_handle_memory_usage();
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87 static long weak_global_handle_memory_usage();
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88
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89 // Garbage collection support(global handles only, local handles are traversed from thread)
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90 // Traversal of regular global handles
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91 static void oops_do(OopClosure* f);
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92 // Traversal of weak global handles. Unreachable oops are cleared.
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93 static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
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94 };
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95
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96
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97
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98 // JNI handle blocks holding local/global JNI handles
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99
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100 class JNIHandleBlock : public CHeapObj {
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101 friend class VMStructs;
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102 private:
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103 enum SomeConstants {
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104 block_size_in_oops = 32 // Number of handles per handle block
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105 };
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106
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107 oop _handles[block_size_in_oops]; // The handles
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108 int _top; // Index of next unused handle
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109 JNIHandleBlock* _next; // Link to next block
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110
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111 // The following instance variables are only used by the first block in a chain.
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112 // Having two types of blocks complicates the code and the space overhead in negligble.
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113 JNIHandleBlock* _last; // Last block in use
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114 JNIHandleBlock* _pop_frame_link; // Block to restore on PopLocalFrame call
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115 oop* _free_list; // Handle free list
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116 int _allocate_before_rebuild; // Number of blocks to allocate before rebuilding free list
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117
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118 #ifndef PRODUCT
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119 JNIHandleBlock* _block_list_link; // Link for list below
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120 static JNIHandleBlock* _block_list; // List of all allocated blocks (for debugging only)
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121 #endif
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122
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123 static JNIHandleBlock* _block_free_list; // Free list of currently unused blocks
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124 static int _blocks_allocated; // For debugging/printing
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125
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126 // Fill block with bad_handle values
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127 void zap();
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128
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129 // No more handles in the both the current and following blocks
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130 void clear() { _top = 0; }
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131
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132 // Free list computation
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133 void rebuild_free_list();
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134
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135 public:
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136 // Handle allocation
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137 jobject allocate_handle(oop obj);
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138
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139 // Block allocation and block free list management
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140 static JNIHandleBlock* allocate_block(Thread* thread = NULL);
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141 static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
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142
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143 // JNI PushLocalFrame/PopLocalFrame support
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144 JNIHandleBlock* pop_frame_link() const { return _pop_frame_link; }
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145 void set_pop_frame_link(JNIHandleBlock* block) { _pop_frame_link = block; }
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146
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147 // Stub generator support
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148 static int top_offset_in_bytes() { return offset_of(JNIHandleBlock, _top); }
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149
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150 // Garbage collection support
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151 // Traversal of regular handles
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152 void oops_do(OopClosure* f);
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153 // Traversal of weak handles. Unreachable oops are cleared.
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154 void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
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155
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156 // Debugging
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157 bool chain_contains(jobject handle) const; // Does this block or following blocks contain handle
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158 bool contains(jobject handle) const; // Does this block contain handle
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159 int length() const; // Length of chain starting with this block
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160 long memory_usage() const;
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161 #ifndef PRODUCT
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162 static bool any_contains(jobject handle); // Does any block currently in use contain handle
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163 static void print_statistics();
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164 #endif
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165 };
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166
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167
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168 inline oop JNIHandles::resolve(jobject handle) {
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169 oop result = (handle == NULL ? (oop)NULL : *(oop*)handle);
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170 assert(result != NULL || (handle == NULL || !CheckJNICalls || is_weak_global_handle(handle)), "Invalid value read from jni handle");
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171 assert(result != badJNIHandle, "Pointing to zapped jni handle area");
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172 return result;
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173 };
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174
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175
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176 inline oop JNIHandles::resolve_external_guard(jobject handle) {
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177 if (handle == NULL) return NULL;
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178 oop result = *(oop*)handle;
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179 if (result == NULL || result == badJNIHandle) return NULL;
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180 return result;
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181 };
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182
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183
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184 inline oop JNIHandles::resolve_non_null(jobject handle) {
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185 assert(handle != NULL, "JNI handle should not be null");
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186 oop result = *(oop*)handle;
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187 assert(result != NULL, "Invalid value read from jni handle");
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188 assert(result != badJNIHandle, "Pointing to zapped jni handle area");
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189 // Don't let that private _deleted_handle object escape into the wild.
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190 assert(result != deleted_handle(), "Used a deleted global handle.");
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191 return result;
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192 };
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193
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194 inline methodOop JNIHandles::resolve_jmethod_id(jmethodID mid) {
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195 return (methodOop) resolve_non_null((jobject)mid);
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196 };
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197
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198 inline methodOop JNIHandles::checked_resolve_jmethod_id(jmethodID mid) {
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199 jobject handle = (jobject)mid;
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200 if (is_weak_global_handle(handle)) {
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201 return (methodOop) resolve_non_null(handle);
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202 } else {
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203 return (methodOop) NULL;
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204 }
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205 };
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206
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207
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208 inline void JNIHandles::destroy_local(jobject handle) {
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209 if (handle != NULL) {
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210 *((oop*)handle) = deleted_handle(); // Mark the handle as deleted, allocate will reuse it
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211 }
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212 }
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