1 /*
   2  * Copyright (c) 2000, 2015, 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.nio;
  27 
  28 import java.security.AccessController;
  29 import java.util.concurrent.atomic.AtomicLong;
  30 import java.util.concurrent.atomic.LongAdder;
  31 
  32 import sun.misc.JavaLangRefAccess;
  33 import sun.misc.SharedSecrets;
  34 import sun.misc.Unsafe;
  35 import sun.misc.VM;
  36 
  37 /**
  38  * Access to bits, native and otherwise.
  39  */
  40 
  41 class Bits {                            // package-private
  42 
  43     private Bits() { }
  44 
  45 
  46     // -- Swapping --
  47 
  48     static short swap(short x) {
  49         return Short.reverseBytes(x);
  50     }
  51 
  52     static char swap(char x) {
  53         return Character.reverseBytes(x);
  54     }
  55 
  56     static int swap(int x) {
  57         return Integer.reverseBytes(x);
  58     }
  59 
  60     static long swap(long x) {
  61         return Long.reverseBytes(x);
  62     }
  63 
  64 
  65     // -- get/put char --
  66 
  67     static private char makeChar(byte b1, byte b0) {
  68         return (char)((b1 << 8) | (b0 & 0xff));
  69     }
  70 
  71     static char getCharL(ByteBuffer bb, int bi) {
  72         return makeChar(bb._get(bi + 1),
  73                         bb._get(bi    ));
  74     }
  75 
  76     static char getCharL(long a) {
  77         return makeChar(_get(a + 1),
  78                         _get(a    ));
  79     }
  80 
  81     static char getCharB(ByteBuffer bb, int bi) {
  82         return makeChar(bb._get(bi    ),
  83                         bb._get(bi + 1));
  84     }
  85 
  86     static char getCharB(long a) {
  87         return makeChar(_get(a    ),
  88                         _get(a + 1));
  89     }
  90 
  91     static char getChar(ByteBuffer bb, int bi, boolean bigEndian) {
  92         return bigEndian ? getCharB(bb, bi) : getCharL(bb, bi);
  93     }
  94 
  95     static char getChar(long a, boolean bigEndian) {
  96         return bigEndian ? getCharB(a) : getCharL(a);
  97     }
  98 
  99     private static byte char1(char x) { return (byte)(x >> 8); }
 100     private static byte char0(char x) { return (byte)(x     ); }
 101 
 102     static void putCharL(ByteBuffer bb, int bi, char x) {
 103         bb._put(bi    , char0(x));
 104         bb._put(bi + 1, char1(x));
 105     }
 106 
 107     static void putCharL(long a, char x) {
 108         _put(a    , char0(x));
 109         _put(a + 1, char1(x));
 110     }
 111 
 112     static void putCharB(ByteBuffer bb, int bi, char x) {
 113         bb._put(bi    , char1(x));
 114         bb._put(bi + 1, char0(x));
 115     }
 116 
 117     static void putCharB(long a, char x) {
 118         _put(a    , char1(x));
 119         _put(a + 1, char0(x));
 120     }
 121 
 122     static void putChar(ByteBuffer bb, int bi, char x, boolean bigEndian) {
 123         if (bigEndian)
 124             putCharB(bb, bi, x);
 125         else
 126             putCharL(bb, bi, x);
 127     }
 128 
 129     static void putChar(long a, char x, boolean bigEndian) {
 130         if (bigEndian)
 131             putCharB(a, x);
 132         else
 133             putCharL(a, x);
 134     }
 135 
 136 
 137     // -- get/put short --
 138 
 139     static private short makeShort(byte b1, byte b0) {
 140         return (short)((b1 << 8) | (b0 & 0xff));
 141     }
 142 
 143     static short getShortL(ByteBuffer bb, int bi) {
 144         return makeShort(bb._get(bi + 1),
 145                          bb._get(bi    ));
 146     }
 147 
 148     static short getShortL(long a) {
 149         return makeShort(_get(a + 1),
 150                          _get(a    ));
 151     }
 152 
 153     static short getShortB(ByteBuffer bb, int bi) {
 154         return makeShort(bb._get(bi    ),
 155                          bb._get(bi + 1));
 156     }
 157 
 158     static short getShortB(long a) {
 159         return makeShort(_get(a    ),
 160                          _get(a + 1));
 161     }
 162 
 163     static short getShort(ByteBuffer bb, int bi, boolean bigEndian) {
 164         return bigEndian ? getShortB(bb, bi) : getShortL(bb, bi);
 165     }
 166 
 167     static short getShort(long a, boolean bigEndian) {
 168         return bigEndian ? getShortB(a) : getShortL(a);
 169     }
 170 
 171     private static byte short1(short x) { return (byte)(x >> 8); }
 172     private static byte short0(short x) { return (byte)(x     ); }
 173 
 174     static void putShortL(ByteBuffer bb, int bi, short x) {
 175         bb._put(bi    , short0(x));
 176         bb._put(bi + 1, short1(x));
 177     }
 178 
 179     static void putShortL(long a, short x) {
 180         _put(a    , short0(x));
 181         _put(a + 1, short1(x));
 182     }
 183 
 184     static void putShortB(ByteBuffer bb, int bi, short x) {
 185         bb._put(bi    , short1(x));
 186         bb._put(bi + 1, short0(x));
 187     }
 188 
 189     static void putShortB(long a, short x) {
 190         _put(a    , short1(x));
 191         _put(a + 1, short0(x));
 192     }
 193 
 194     static void putShort(ByteBuffer bb, int bi, short x, boolean bigEndian) {
 195         if (bigEndian)
 196             putShortB(bb, bi, x);
 197         else
 198             putShortL(bb, bi, x);
 199     }
 200 
 201     static void putShort(long a, short x, boolean bigEndian) {
 202         if (bigEndian)
 203             putShortB(a, x);
 204         else
 205             putShortL(a, x);
 206     }
 207 
 208 
 209     // -- get/put int --
 210 
 211     static private int makeInt(byte b3, byte b2, byte b1, byte b0) {
 212         return (((b3       ) << 24) |
 213                 ((b2 & 0xff) << 16) |
 214                 ((b1 & 0xff) <<  8) |
 215                 ((b0 & 0xff)      ));
 216     }
 217 
 218     static int getIntL(ByteBuffer bb, int bi) {
 219         return makeInt(bb._get(bi + 3),
 220                        bb._get(bi + 2),
 221                        bb._get(bi + 1),
 222                        bb._get(bi    ));
 223     }
 224 
 225     static int getIntL(long a) {
 226         return makeInt(_get(a + 3),
 227                        _get(a + 2),
 228                        _get(a + 1),
 229                        _get(a    ));
 230     }
 231 
 232     static int getIntB(ByteBuffer bb, int bi) {
 233         return makeInt(bb._get(bi    ),
 234                        bb._get(bi + 1),
 235                        bb._get(bi + 2),
 236                        bb._get(bi + 3));
 237     }
 238 
 239     static int getIntB(long a) {
 240         return makeInt(_get(a    ),
 241                        _get(a + 1),
 242                        _get(a + 2),
 243                        _get(a + 3));
 244     }
 245 
 246     static int getInt(ByteBuffer bb, int bi, boolean bigEndian) {
 247         return bigEndian ? getIntB(bb, bi) : getIntL(bb, bi) ;
 248     }
 249 
 250     static int getInt(long a, boolean bigEndian) {
 251         return bigEndian ? getIntB(a) : getIntL(a) ;
 252     }
 253 
 254     private static byte int3(int x) { return (byte)(x >> 24); }
 255     private static byte int2(int x) { return (byte)(x >> 16); }
 256     private static byte int1(int x) { return (byte)(x >>  8); }
 257     private static byte int0(int x) { return (byte)(x      ); }
 258 
 259     static void putIntL(ByteBuffer bb, int bi, int x) {
 260         bb._put(bi + 3, int3(x));
 261         bb._put(bi + 2, int2(x));
 262         bb._put(bi + 1, int1(x));
 263         bb._put(bi    , int0(x));
 264     }
 265 
 266     static void putIntL(long a, int x) {
 267         _put(a + 3, int3(x));
 268         _put(a + 2, int2(x));
 269         _put(a + 1, int1(x));
 270         _put(a    , int0(x));
 271     }
 272 
 273     static void putIntB(ByteBuffer bb, int bi, int x) {
 274         bb._put(bi    , int3(x));
 275         bb._put(bi + 1, int2(x));
 276         bb._put(bi + 2, int1(x));
 277         bb._put(bi + 3, int0(x));
 278     }
 279 
 280     static void putIntB(long a, int x) {
 281         _put(a    , int3(x));
 282         _put(a + 1, int2(x));
 283         _put(a + 2, int1(x));
 284         _put(a + 3, int0(x));
 285     }
 286 
 287     static void putInt(ByteBuffer bb, int bi, int x, boolean bigEndian) {
 288         if (bigEndian)
 289             putIntB(bb, bi, x);
 290         else
 291             putIntL(bb, bi, x);
 292     }
 293 
 294     static void putInt(long a, int x, boolean bigEndian) {
 295         if (bigEndian)
 296             putIntB(a, x);
 297         else
 298             putIntL(a, x);
 299     }
 300 
 301 
 302     // -- get/put long --
 303 
 304     static private long makeLong(byte b7, byte b6, byte b5, byte b4,
 305                                  byte b3, byte b2, byte b1, byte b0)
 306     {
 307         return ((((long)b7       ) << 56) |
 308                 (((long)b6 & 0xff) << 48) |
 309                 (((long)b5 & 0xff) << 40) |
 310                 (((long)b4 & 0xff) << 32) |
 311                 (((long)b3 & 0xff) << 24) |
 312                 (((long)b2 & 0xff) << 16) |
 313                 (((long)b1 & 0xff) <<  8) |
 314                 (((long)b0 & 0xff)      ));
 315     }
 316 
 317     static long getLongL(ByteBuffer bb, int bi) {
 318         return makeLong(bb._get(bi + 7),
 319                         bb._get(bi + 6),
 320                         bb._get(bi + 5),
 321                         bb._get(bi + 4),
 322                         bb._get(bi + 3),
 323                         bb._get(bi + 2),
 324                         bb._get(bi + 1),
 325                         bb._get(bi    ));
 326     }
 327 
 328     static long getLongL(long a) {
 329         return makeLong(_get(a + 7),
 330                         _get(a + 6),
 331                         _get(a + 5),
 332                         _get(a + 4),
 333                         _get(a + 3),
 334                         _get(a + 2),
 335                         _get(a + 1),
 336                         _get(a    ));
 337     }
 338 
 339     static long getLongB(ByteBuffer bb, int bi) {
 340         return makeLong(bb._get(bi    ),
 341                         bb._get(bi + 1),
 342                         bb._get(bi + 2),
 343                         bb._get(bi + 3),
 344                         bb._get(bi + 4),
 345                         bb._get(bi + 5),
 346                         bb._get(bi + 6),
 347                         bb._get(bi + 7));
 348     }
 349 
 350     static long getLongB(long a) {
 351         return makeLong(_get(a    ),
 352                         _get(a + 1),
 353                         _get(a + 2),
 354                         _get(a + 3),
 355                         _get(a + 4),
 356                         _get(a + 5),
 357                         _get(a + 6),
 358                         _get(a + 7));
 359     }
 360 
 361     static long getLong(ByteBuffer bb, int bi, boolean bigEndian) {
 362         return bigEndian ? getLongB(bb, bi) : getLongL(bb, bi);
 363     }
 364 
 365     static long getLong(long a, boolean bigEndian) {
 366         return bigEndian ? getLongB(a) : getLongL(a);
 367     }
 368 
 369     private static byte long7(long x) { return (byte)(x >> 56); }
 370     private static byte long6(long x) { return (byte)(x >> 48); }
 371     private static byte long5(long x) { return (byte)(x >> 40); }
 372     private static byte long4(long x) { return (byte)(x >> 32); }
 373     private static byte long3(long x) { return (byte)(x >> 24); }
 374     private static byte long2(long x) { return (byte)(x >> 16); }
 375     private static byte long1(long x) { return (byte)(x >>  8); }
 376     private static byte long0(long x) { return (byte)(x      ); }
 377 
 378     static void putLongL(ByteBuffer bb, int bi, long x) {
 379         bb._put(bi + 7, long7(x));
 380         bb._put(bi + 6, long6(x));
 381         bb._put(bi + 5, long5(x));
 382         bb._put(bi + 4, long4(x));
 383         bb._put(bi + 3, long3(x));
 384         bb._put(bi + 2, long2(x));
 385         bb._put(bi + 1, long1(x));
 386         bb._put(bi    , long0(x));
 387     }
 388 
 389     static void putLongL(long a, long x) {
 390         _put(a + 7, long7(x));
 391         _put(a + 6, long6(x));
 392         _put(a + 5, long5(x));
 393         _put(a + 4, long4(x));
 394         _put(a + 3, long3(x));
 395         _put(a + 2, long2(x));
 396         _put(a + 1, long1(x));
 397         _put(a    , long0(x));
 398     }
 399 
 400     static void putLongB(ByteBuffer bb, int bi, long x) {
 401         bb._put(bi    , long7(x));
 402         bb._put(bi + 1, long6(x));
 403         bb._put(bi + 2, long5(x));
 404         bb._put(bi + 3, long4(x));
 405         bb._put(bi + 4, long3(x));
 406         bb._put(bi + 5, long2(x));
 407         bb._put(bi + 6, long1(x));
 408         bb._put(bi + 7, long0(x));
 409     }
 410 
 411     static void putLongB(long a, long x) {
 412         _put(a    , long7(x));
 413         _put(a + 1, long6(x));
 414         _put(a + 2, long5(x));
 415         _put(a + 3, long4(x));
 416         _put(a + 4, long3(x));
 417         _put(a + 5, long2(x));
 418         _put(a + 6, long1(x));
 419         _put(a + 7, long0(x));
 420     }
 421 
 422     static void putLong(ByteBuffer bb, int bi, long x, boolean bigEndian) {
 423         if (bigEndian)
 424             putLongB(bb, bi, x);
 425         else
 426             putLongL(bb, bi, x);
 427     }
 428 
 429     static void putLong(long a, long x, boolean bigEndian) {
 430         if (bigEndian)
 431             putLongB(a, x);
 432         else
 433             putLongL(a, x);
 434     }
 435 
 436 
 437     // -- get/put float --
 438 
 439     static float getFloatL(ByteBuffer bb, int bi) {
 440         return Float.intBitsToFloat(getIntL(bb, bi));
 441     }
 442 
 443     static float getFloatL(long a) {
 444         return Float.intBitsToFloat(getIntL(a));
 445     }
 446 
 447     static float getFloatB(ByteBuffer bb, int bi) {
 448         return Float.intBitsToFloat(getIntB(bb, bi));
 449     }
 450 
 451     static float getFloatB(long a) {
 452         return Float.intBitsToFloat(getIntB(a));
 453     }
 454 
 455     static float getFloat(ByteBuffer bb, int bi, boolean bigEndian) {
 456         return bigEndian ? getFloatB(bb, bi) : getFloatL(bb, bi);
 457     }
 458 
 459     static float getFloat(long a, boolean bigEndian) {
 460         return bigEndian ? getFloatB(a) : getFloatL(a);
 461     }
 462 
 463     static void putFloatL(ByteBuffer bb, int bi, float x) {
 464         putIntL(bb, bi, Float.floatToRawIntBits(x));
 465     }
 466 
 467     static void putFloatL(long a, float x) {
 468         putIntL(a, Float.floatToRawIntBits(x));
 469     }
 470 
 471     static void putFloatB(ByteBuffer bb, int bi, float x) {
 472         putIntB(bb, bi, Float.floatToRawIntBits(x));
 473     }
 474 
 475     static void putFloatB(long a, float x) {
 476         putIntB(a, Float.floatToRawIntBits(x));
 477     }
 478 
 479     static void putFloat(ByteBuffer bb, int bi, float x, boolean bigEndian) {
 480         if (bigEndian)
 481             putFloatB(bb, bi, x);
 482         else
 483             putFloatL(bb, bi, x);
 484     }
 485 
 486     static void putFloat(long a, float x, boolean bigEndian) {
 487         if (bigEndian)
 488             putFloatB(a, x);
 489         else
 490             putFloatL(a, x);
 491     }
 492 
 493 
 494     // -- get/put double --
 495 
 496     static double getDoubleL(ByteBuffer bb, int bi) {
 497         return Double.longBitsToDouble(getLongL(bb, bi));
 498     }
 499 
 500     static double getDoubleL(long a) {
 501         return Double.longBitsToDouble(getLongL(a));
 502     }
 503 
 504     static double getDoubleB(ByteBuffer bb, int bi) {
 505         return Double.longBitsToDouble(getLongB(bb, bi));
 506     }
 507 
 508     static double getDoubleB(long a) {
 509         return Double.longBitsToDouble(getLongB(a));
 510     }
 511 
 512     static double getDouble(ByteBuffer bb, int bi, boolean bigEndian) {
 513         return bigEndian ? getDoubleB(bb, bi) : getDoubleL(bb, bi);
 514     }
 515 
 516     static double getDouble(long a, boolean bigEndian) {
 517         return bigEndian ? getDoubleB(a) : getDoubleL(a);
 518     }
 519 
 520     static void putDoubleL(ByteBuffer bb, int bi, double x) {
 521         putLongL(bb, bi, Double.doubleToRawLongBits(x));
 522     }
 523 
 524     static void putDoubleL(long a, double x) {
 525         putLongL(a, Double.doubleToRawLongBits(x));
 526     }
 527 
 528     static void putDoubleB(ByteBuffer bb, int bi, double x) {
 529         putLongB(bb, bi, Double.doubleToRawLongBits(x));
 530     }
 531 
 532     static void putDoubleB(long a, double x) {
 533         putLongB(a, Double.doubleToRawLongBits(x));
 534     }
 535 
 536     static void putDouble(ByteBuffer bb, int bi, double x, boolean bigEndian) {
 537         if (bigEndian)
 538             putDoubleB(bb, bi, x);
 539         else
 540             putDoubleL(bb, bi, x);
 541     }
 542 
 543     static void putDouble(long a, double x, boolean bigEndian) {
 544         if (bigEndian)
 545             putDoubleB(a, x);
 546         else
 547             putDoubleL(a, x);
 548     }
 549 
 550 
 551     // -- Unsafe access --
 552 
 553     private static final Unsafe unsafe = Unsafe.getUnsafe();
 554 
 555     private static byte _get(long a) {
 556         return unsafe.getByte(a);
 557     }
 558 
 559     private static void _put(long a, byte b) {
 560         unsafe.putByte(a, b);
 561     }
 562 
 563     static Unsafe unsafe() {
 564         return unsafe;
 565     }
 566 
 567 
 568     // -- Processor and memory-system properties --
 569 
 570     private static final ByteOrder byteOrder
 571         = unsafe.isBigEndian() ? ByteOrder.BIG_ENDIAN : ByteOrder.LITTLE_ENDIAN;
 572 
 573     static ByteOrder byteOrder() {
 574         return byteOrder;
 575     }
 576 
 577     private static int pageSize = -1;
 578 
 579     static int pageSize() {
 580         if (pageSize == -1)
 581             pageSize = unsafe().pageSize();
 582         return pageSize;
 583     }
 584 
 585     static int pageCount(long size) {
 586         return (int)(size + (long)pageSize() - 1L) / pageSize();
 587     }
 588 
 589     private static boolean unaligned = unsafe.unalignedAccess();
 590 
 591     static boolean unaligned() {
 592         return unaligned;
 593     }
 594 
 595 
 596     // -- Direct memory management --
 597 
 598     // A user-settable upper limit on the maximum amount of allocatable
 599     // direct buffer memory.  This value may be changed during VM
 600     // initialization if it is launched with "-XX:MaxDirectMemorySize=<size>".
 601     private static volatile long maxMemory = VM.maxDirectMemory();
 602     private static final AtomicLong reservedMemory = new AtomicLong();
 603     private static final AtomicLong totalCapacity = new AtomicLong();
 604     private static final AtomicLong count = new AtomicLong();
 605     private static volatile boolean memoryLimitSet = false;
 606     // max. number of sleeps during try-reserving with exponentially
 607     // increasing delay before throwing OutOfMemoryError:
 608     // 1, 2, 4, 8, 16, 32, 64, 128, 256 (total 511 ms ~ 0.5 s)
 609     // which means that OOME will be thrown after 0.5 s of trying
 610     private static final int MAX_SLEEPS = 9;
 611 
 612     // These methods should be called whenever direct memory is allocated or
 613     // freed.  They allow the user to control the amount of direct memory
 614     // which a process may access.  All sizes are specified in bytes.
 615     static void reserveMemory(long size, int cap) {
 616 
 617         if (!memoryLimitSet && VM.isBooted()) {
 618             maxMemory = VM.maxDirectMemory();
 619             memoryLimitSet = true;
 620         }
 621 
 622         // optimist!
 623         if (tryReserveMemory(size, cap)) {
 624             return;
 625         }
 626 
 627         final JavaLangRefAccess jlra = SharedSecrets.getJavaLangRefAccess();
 628 
 629         // retry while helping enqueue pending Reference objects
 630         // which includes executing pending Cleaner(s) which includes
 631         // Cleaner(s) that free direct buffer memory
 632         while (jlra.tryHandlePendingReference()) {
 633             if (tryReserveMemory(size, cap)) {
 634                 return;
 635             }
 636         }
 637 
 638         // trigger VM's Reference processing
 639         System.gc();
 640 
 641         // a retry loop with exponential back-off delays
 642         // (this gives VM some time to do it's job)
 643         boolean interrupted = false;
 644         try {
 645             long sleepTime = 1;
 646             int sleeps = 0;
 647             while (true) {
 648                 if (tryReserveMemory(size, cap)) {
 649                     return;
 650                 }
 651                 if (sleeps >= MAX_SLEEPS) {
 652                     break;
 653                 }
 654                 if (!jlra.tryHandlePendingReference()) {
 655                     try {
 656                         Thread.sleep(sleepTime);
 657                         sleepTime <<= 1;
 658                         sleeps++;
 659                     } catch (InterruptedException e) {
 660                         interrupted = true;
 661                     }
 662                 }
 663             }
 664 
 665             // no luck
 666             throw new OutOfMemoryError("Direct buffer memory");
 667 
 668         } finally {
 669             if (interrupted) {
 670                 // don't swallow interrupts
 671                 Thread.currentThread().interrupt();
 672             }
 673         }
 674     }
 675 
 676     private static boolean tryReserveMemory(long size, int cap) {
 677 
 678         // -XX:MaxDirectMemorySize limits the total capacity rather than the
 679         // actual memory usage, which will differ when buffers are page
 680         // aligned.
 681         long totalCap;
 682         while (cap <= maxMemory - (totalCap = totalCapacity.get())) {
 683             if (totalCapacity.compareAndSet(totalCap, totalCap + cap)) {
 684                 reservedMemory.addAndGet(size);
 685                 count.incrementAndGet();
 686                 return true;
 687             }
 688         }
 689 
 690         return false;
 691     }
 692 
 693 
 694     static void unreserveMemory(long size, int cap) {
 695         long cnt = count.decrementAndGet();
 696         long reservedMem = reservedMemory.addAndGet(-size);
 697         long totalCap = totalCapacity.addAndGet(-cap);
 698         assert cnt >= 0 && reservedMem >= 0 && totalCap >= 0;
 699     }
 700 
 701     // -- Monitoring of direct buffer usage --
 702 
 703     static {
 704         // setup access to this package in SharedSecrets
 705         sun.misc.SharedSecrets.setJavaNioAccess(
 706             new sun.misc.JavaNioAccess() {
 707                 @Override
 708                 public sun.misc.JavaNioAccess.BufferPool getDirectBufferPool() {
 709                     return new sun.misc.JavaNioAccess.BufferPool() {
 710                         @Override
 711                         public String getName() {
 712                             return "direct";
 713                         }
 714                         @Override
 715                         public long getCount() {
 716                             return Bits.count.get();
 717                         }
 718                         @Override
 719                         public long getTotalCapacity() {
 720                             return Bits.totalCapacity.get();
 721                         }
 722                         @Override
 723                         public long getMemoryUsed() {
 724                             return Bits.reservedMemory.get();
 725                         }
 726                     };
 727                 }
 728                 @Override
 729                 public ByteBuffer newDirectByteBuffer(long addr, int cap, Object ob) {
 730                     return new DirectByteBuffer(addr, cap, ob);
 731                 }
 732                 @Override
 733                 public void truncate(Buffer buf) {
 734                     buf.truncate();
 735                 }
 736         });
 737     }
 738 
 739     // -- Bulk get/put acceleration --
 740 
 741     // These numbers represent the point at which we have empirically
 742     // determined that the average cost of a JNI call exceeds the expense
 743     // of an element by element copy.  These numbers may change over time.
 744     static final int JNI_COPY_TO_ARRAY_THRESHOLD   = 6;
 745     static final int JNI_COPY_FROM_ARRAY_THRESHOLD = 6;
 746 
 747     // This number limits the number of bytes to copy per call to Unsafe's
 748     // copyMemory method. A limit is imposed to allow for safepoint polling
 749     // during a large copy
 750     static final long UNSAFE_COPY_THRESHOLD = 1024L * 1024L;
 751 
 752     // These methods do no bounds checking.  Verification that the copy will not
 753     // result in memory corruption should be done prior to invocation.
 754     // All positions and lengths are specified in bytes.
 755 
 756     /**
 757      * Copy from given source array to destination address.
 758      *
 759      * @param   src
 760      *          source array
 761      * @param   srcBaseOffset
 762      *          offset of first element of storage in source array
 763      * @param   srcPos
 764      *          offset within source array of the first element to read
 765      * @param   dstAddr
 766      *          destination address
 767      * @param   length
 768      *          number of bytes to copy
 769      */
 770     static void copyFromArray(Object src, long srcBaseOffset, long srcPos,
 771                               long dstAddr, long length)
 772     {
 773         long offset = srcBaseOffset + srcPos;
 774         while (length > 0) {
 775             long size = (length > UNSAFE_COPY_THRESHOLD) ? UNSAFE_COPY_THRESHOLD : length;
 776             unsafe.copyMemory(src, offset, null, dstAddr, size);
 777             length -= size;
 778             offset += (size << 1);
 779             dstAddr += size;
 780         }
 781     }
 782 
 783     /**
 784      * Copy from source address into given destination array.
 785      *
 786      * @param   srcAddr
 787      *          source address
 788      * @param   dst
 789      *          destination array
 790      * @param   dstBaseOffset
 791      *          offset of first element of storage in destination array
 792      * @param   dstPos
 793      *          offset within destination array of the first element to write
 794      * @param   length
 795      *          number of bytes to copy
 796      */
 797     static void copyToArray(long srcAddr, Object dst, long dstBaseOffset, long dstPos,
 798                             long length)
 799     {
 800         long offset = dstBaseOffset + dstPos;
 801         while (length > 0) {
 802             long size = (length > UNSAFE_COPY_THRESHOLD) ? UNSAFE_COPY_THRESHOLD : length;
 803             unsafe.copyMemory(null, srcAddr, dst, offset, size);
 804             length -= size;
 805             srcAddr += size;
 806             offset += (size << 1);
 807         }
 808     }
 809 
 810     static void copyFromCharArray(Object src, long srcPos, long dstAddr,
 811                                   long length)
 812     {
 813         copyFromShortArray(src, srcPos, dstAddr, length);
 814     }
 815 
 816     static void copyToCharArray(long srcAddr, Object dst, long dstPos,
 817                                 long length)
 818     {
 819         copyToShortArray(srcAddr, dst, dstPos, length);
 820     }
 821 
 822     static native void copyFromShortArray(Object src, long srcPos, long dstAddr,
 823                                           long length);
 824     static native void copyToShortArray(long srcAddr, Object dst, long dstPos,
 825                                         long length);
 826 
 827     static native void copyFromIntArray(Object src, long srcPos, long dstAddr,
 828                                         long length);
 829     static native void copyToIntArray(long srcAddr, Object dst, long dstPos,
 830                                       long length);
 831 
 832     static native void copyFromLongArray(Object src, long srcPos, long dstAddr,
 833                                          long length);
 834     static native void copyToLongArray(long srcAddr, Object dst, long dstPos,
 835                                        long length);
 836 
 837 }