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hotspot/src/share/vm/code/oopRecorder.hpp

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+/*
+ * Copyright 1998-2005 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+// Recording and retrieval of oop relocations in compiled code.
+
+class CodeBlob;
+
+class OopRecorder : public ResourceObj {
+ public:
+  // A two-way mapping from positive indexes to oop handles.
+  // The zero index is reserved for a constant (sharable) null.
+  // Indexes may not be negative.
+
+  // Use the given arena to manage storage, if not NULL.
+  // By default, uses the current ResourceArea.
+  OopRecorder(Arena* arena = NULL);
+
+  // Generate a new index on which CodeBlob::oop_addr_at will work.
+  // allocate_index and find_index never return the same index,
+  // and allocate_index never returns the same index twice.
+  // In fact, two successive calls to allocate_index return successive ints.
+  int allocate_index(jobject h) {
+    return add_handle(h, false);
+  }
+
+  // For a given jobject, this will return the same index repeatedly.
+  // The index can later be given to oop_at to retrieve the oop.
+  // However, the oop must not be changed via CodeBlob::oop_addr_at.
+  int find_index(jobject h) {
+    int index = maybe_find_index(h);
+    if (index < 0) {  // previously unallocated
+      index = add_handle(h, true);
+    }
+    return index;
+  }
+
+  // variant of find_index which does not allocate if not found (yields -1)
+  int maybe_find_index(jobject h);
+
+  // returns the size of the generated oop table, for sizing the CodeBlob.
+  // must be called after all oops are allocated!
+  int oop_size();
+
+  // Retrieve the oop handle at a given index.
+  jobject handle_at(int index);
+
+  int element_count() {
+    // there is always a NULL virtually present as first object
+    return _handles->length() + first_index;
+  }
+
+  // copy the generated oop table to CodeBlob
+  void copy_to(CodeBlob* code);  // => code->copy_oops(_handles)
+
+  bool is_unused() { return _handles == NULL && !_complete; }
+#ifdef ASSERT
+  bool is_complete() { return _complete; }
+#endif
+
+ private:
+  // leaky hash table of handle => index, to help detect duplicate insertion
+  class IndexCache: public ResourceObj {
+    // This class is only used by the OopRecorder class.
+    friend class OopRecorder;
+    enum {
+      _log_cache_size = 9,
+      _cache_size = (1<<_log_cache_size),
+      // Index entries are ints.  The LSBit is a collision indicator.
+      _collision_bit_shift = 0,
+      _collision_bit = 1,
+      _index_shift = _collision_bit_shift+1
+    };
+    int _cache[_cache_size];
+    static juint cache_index(jobject handle) {
+      juint ci = (int) (intptr_t) handle;
+      ci ^= ci >> (BitsPerByte*2);
+      ci += ci >> (BitsPerByte*1);
+      return ci & (_cache_size-1);
+    }
+    int* cache_location(jobject handle) {
+      return &_cache[ cache_index(handle) ];
+    }
+    static bool cache_location_collision(int* cloc) {
+      return ((*cloc) & _collision_bit) != 0;
+    }
+    static int cache_location_index(int* cloc) {
+      return (*cloc) >> _index_shift;
+    }
+    static void set_cache_location_index(int* cloc, int index) {
+      int cval0 = (*cloc);
+      int cval1 = (index << _index_shift);
+      if (cval0 != 0 && cval1 != cval0)  cval1 += _collision_bit;
+      (*cloc) = cval1;
+    }
+    IndexCache();
+  };
+
+  // Helper function; returns false for NULL or Universe::non_oop_word().
+  inline bool is_real_jobject(jobject h);
+
+  void maybe_initialize();
+  int add_handle(jobject h, bool make_findable);
+
+  enum { null_index = 0, first_index = 1, index_cache_threshold = 20 };
+
+  GrowableArray<jobject>*   _handles;  // ordered list (first is always NULL)
+  GrowableArray<int>*       _no_finds; // all unfindable indexes; usually empty
+  IndexCache*               _indexes;  // map: jobject -> its probable index
+  Arena*                    _arena;
+  bool                      _complete;
+
+#ifdef ASSERT
+  static int _find_index_calls, _hit_indexes, _missed_indexes;
+#endif
+};