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   inline static void destroy_local(jobject handle);
  89 
  90   // Global handles
  91   static jobject make_global(Handle  obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
  92   static void destroy_global(jobject handle);
  93 
  94   // Weak global handles
  95   static jobject make_weak_global(Handle obj, AllocFailType alloc_failmode = AllocFailStrategy::EXIT_OOM);
  96   static void destroy_weak_global(jobject handle);
  97   static bool is_global_weak_cleared(jweak handle); // Test jweak without resolution
  98 
  99   // Initialization
 100   static void initialize();
 101 
 102   // Debugging
 103   static void print_on(outputStream* st);
 104   static void print();
 105   static void verify();
 106   // The category predicates all require handle != NULL.
 107   static bool is_local_handle(Thread* thread, jobject handle);
 108   static bool is_frame_handle(JavaThread* thread, jobject handle);
 109   static bool is_global_handle(jobject handle);
 110   static bool is_weak_global_handle(jobject handle);
 111   static size_t global_handle_memory_usage();
 112   static size_t weak_global_handle_memory_usage();
 113 
 114 #ifndef PRODUCT
 115   // Is handle from any local block of any thread?
 116   static bool is_local_handle(jobject handle);
 117 #endif
 118 
 119   // precondition: handle != NULL.
 120   static jobjectRefType handle_type(Thread* thread, jobject handle);
 121 
 122   // Garbage collection support(global handles only, local handles are traversed from thread)
 123   // Traversal of regular global handles
 124   static void oops_do(OopClosure* f);
 125   // Traversal of weak global handles. Unreachable oops are cleared.
 126   static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
 127   // Traversal of weak global handles.
 128   static void weak_oops_do(OopClosure* f);
 129 
 130   static bool is_global_storage(const OopStorage* storage);
 131 };
 132 
 133 
 134 
 135 // JNI handle blocks holding local/global JNI handles
 136 
 137 class JNIHandleBlock : public CHeapObj<mtInternal> {
 138   friend class VMStructs;
 139   friend class ZeroInterpreter;
 140 
 141  private:
 142   enum SomeConstants {
 143     block_size_in_oops  = 32                    // Number of handles per handle block
 144   };
 145 
 146   uintptr_t       _handles[block_size_in_oops]; // The handles
 147   int             _top;                         // Index of next unused handle
 148   JNIHandleBlock* _next;                        // Link to next block
 149 
 150   // The following instance variables are only used by the first block in a chain.
 151   // Having two types of blocks complicates the code and the space overhead in negligible.
 152   JNIHandleBlock* _last;                        // Last block in use
 153   JNIHandleBlock* _pop_frame_link;              // Block to restore on PopLocalFrame call
 154   uintptr_t*      _free_list;                   // Handle free list
 155   int             _allocate_before_rebuild;     // Number of blocks to allocate before rebuilding free list
 156 
 157   // Check JNI, "planned capacity" for current frame (or push/ensure)
 158   size_t          _planned_capacity;
 159 
 160   #ifndef PRODUCT
 161   JNIHandleBlock* _block_list_link;             // Link for list below
 162   static JNIHandleBlock* _block_list;           // List of all allocated blocks (for debugging only)
 163   #endif
 164 
 165   static JNIHandleBlock* _block_free_list;      // Free list of currently unused blocks
 166   static int      _blocks_allocated;            // For debugging/printing
 167 
 168   // Fill block with bad_handle values
 169   void zap() NOT_DEBUG_RETURN;
 170 
 171   // Free list computation
 172   void rebuild_free_list();
 173 
 174   // No more handles in the both the current and following blocks
 175   void clear() { _top = 0; }
 176 
 177  public:
 178   // Handle allocation
 179   jobject allocate_handle(oop obj);
 180 
 181   // Block allocation and block free list management
 182   static JNIHandleBlock* allocate_block(Thread* thread = NULL);
 183   static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
 184 
 185   // JNI PushLocalFrame/PopLocalFrame support
 186   JNIHandleBlock* pop_frame_link() const          { return _pop_frame_link; }
 187   void set_pop_frame_link(JNIHandleBlock* block)  { _pop_frame_link = block; }
 188 
 189   // Stub generator support
 190   static int top_offset_in_bytes()                { return offset_of(JNIHandleBlock, _top); }
 191 
 192   // Garbage collection support
 193   // Traversal of handles
 194   void oops_do(OopClosure* f);
 195 
 196   // Checked JNI support
 197   void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
 198   const size_t get_planned_capacity() { return _planned_capacity; }
 199   const size_t get_number_of_live_handles();
 200 
 201   // Debugging
 202   bool chain_contains(jobject handle) const;    // Does this block or following blocks contain handle
 203   bool contains(jobject handle) const;          // Does this block contain handle
 204   size_t length() const;                        // Length of chain starting with this block
 205   size_t memory_usage() const;
 206   #ifndef PRODUCT
 207   static bool any_contains(jobject handle);     // Does any block currently in use contain handle
 208   static void print_statistics();
 209   #endif
 210 };
 211 
 212 #endif // SHARE_RUNTIME_JNIHANDLES_HPP