1 /*
   2  * Copyright (c) 1998, 2005, 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 public:
  26   // Java Thread  - force inlining
  27   static inline Thread* thread() ;
  28 
  29 private:
  30   static Thread* _get_thread_cache[];  // index by [(raw_id>>9)^(raw_id>>20) % _pd_cache_size]
  31   static Thread* get_thread_via_cache_slowly(uintptr_t raw_id, int index);
  32 
  33   NOT_PRODUCT(static int _tcacheHit;)
  34   NOT_PRODUCT(static int _tcacheMiss;)
  35 
  36 public:
  37 
  38   // Print cache hit/miss statistics
  39   static void print_statistics() PRODUCT_RETURN;
  40 
  41   enum Constants {
  42     _pd_cache_size         =  256*2  // projected typical # of threads * 2
  43   };
  44 
  45   static void set_thread_in_slot (Thread *) ;
  46 
  47   static uintptr_t pd_raw_thread_id() {
  48     return _raw_thread_id();
  49   }
  50 
  51   static int pd_cache_index(uintptr_t raw_id) {
  52     // Hash function: From email from Dave:
  53     // The hash function deserves an explanation.  %g7 points to libthread's
  54     // "thread" structure.  On T1 the thread structure is allocated on the
  55     // user's stack (yes, really!) so the ">>20" handles T1 where the JVM's
  56     // stack size is usually >= 1Mb.  The ">>9" is for T2 where Roger allocates
  57     // globs of thread blocks contiguously.  The "9" has to do with the
  58     // expected size of the T2 thread structure.  If these constants are wrong
  59     // the worst thing that'll happen is that the hit rate for heavily threaded
  60     // apps won't be as good as it could be.  If you want to burn another
  61     // shift+xor you could mix together _all of the %g7 bits to form the hash,
  62     // but I think that's excessive.  Making the change above changed the
  63     // T$ miss rate on SpecJBB (on a 16X system) from about 3% to imperceptible.
  64     uintptr_t ix = (int) (((raw_id >> 9) ^ (raw_id >> 20)) % _pd_cache_size);
  65     return ix;
  66   }