DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Mercurial (27a812186ff4)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745
/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: sw=4 ts=4 et :
 */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/ipc/MessageChannel.h"
#include "mozilla/ipc/ProtocolUtils.h"

#include "mozilla/Assertions.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/Move.h"
#include "nsDebug.h"
#include "nsISupportsImpl.h"

// Undo the damage done by mozzconf.h
#undef compress

using namespace mozilla;
using namespace std;

using mozilla::MonitorAutoLock;
using mozilla::MonitorAutoUnlock;

template<>
struct RunnableMethodTraits<mozilla::ipc::MessageChannel>
{
    static void RetainCallee(mozilla::ipc::MessageChannel* obj) { }
    static void ReleaseCallee(mozilla::ipc::MessageChannel* obj) { }
};

#define IPC_ASSERT(_cond, ...)                                      \
    do {                                                            \
        if (!(_cond))                                               \
            DebugAbort(__FILE__, __LINE__, #_cond,## __VA_ARGS__);  \
    } while (0)

namespace mozilla {
namespace ipc {

const int32_t MessageChannel::kNoTimeout = INT32_MIN;

// static
bool MessageChannel::sIsPumpingMessages = false;

enum Direction
{
    IN_MESSAGE,
    OUT_MESSAGE
};


class MessageChannel::InterruptFrame
{
private:
    enum Semantics
    {
        INTR_SEMS,
        SYNC_SEMS,
        ASYNC_SEMS
    };

public:
    InterruptFrame(Direction direction, const Message* msg)
      : mMessageName(strdup(msg->name())),
        mMessageRoutingId(msg->routing_id()),
        mMesageSemantics(msg->is_interrupt() ? INTR_SEMS :
                          msg->is_sync() ? SYNC_SEMS :
                          ASYNC_SEMS),
        mDirection(direction),
        mMoved(false)
    {
        MOZ_ASSERT(mMessageName);
    }

    InterruptFrame(InterruptFrame&& aOther)
    {
        MOZ_ASSERT(aOther.mMessageName);
        mMessageName = aOther.mMessageName;
        aOther.mMessageName = nullptr;
        aOther.mMoved = true;

        mMessageRoutingId = aOther.mMessageRoutingId;
        mMesageSemantics = aOther.mMesageSemantics;
        mDirection = aOther.mDirection;
    }

    ~InterruptFrame()
    {
        MOZ_ASSERT_IF(!mMessageName, mMoved);

        if (mMessageName)
            free(const_cast<char*>(mMessageName));
    }

    InterruptFrame& operator=(InterruptFrame&& aOther)
    {
        MOZ_ASSERT(&aOther != this);
        this->~InterruptFrame();
        new (this) InterruptFrame(mozilla::Move(aOther));
        return *this;
    }

    bool IsInterruptIncall() const
    {
        return INTR_SEMS == mMesageSemantics && IN_MESSAGE == mDirection;
    }

    bool IsInterruptOutcall() const
    {
        return INTR_SEMS == mMesageSemantics && OUT_MESSAGE == mDirection;
    }

    void Describe(int32_t* id, const char** dir, const char** sems,
                  const char** name) const
    {
        *id = mMessageRoutingId;
        *dir = (IN_MESSAGE == mDirection) ? "in" : "out";
        *sems = (INTR_SEMS == mMesageSemantics) ? "intr" :
                (SYNC_SEMS == mMesageSemantics) ? "sync" :
                "async";
        *name = mMessageName;
    }

private:
    const char* mMessageName;
    int32_t mMessageRoutingId;
    Semantics mMesageSemantics;
    Direction mDirection;
    DebugOnly<bool> mMoved;

    // Disable harmful methods.
    InterruptFrame(const InterruptFrame& aOther) MOZ_DELETE;
    InterruptFrame& operator=(const InterruptFrame&) MOZ_DELETE;
};

class MOZ_STACK_CLASS MessageChannel::CxxStackFrame
{
public:
    CxxStackFrame(MessageChannel& that, Direction direction, const Message* msg)
      : mThat(that)
    {
        mThat.AssertWorkerThread();

        if (mThat.mCxxStackFrames.empty())
            mThat.EnteredCxxStack();

        mThat.mCxxStackFrames.append(InterruptFrame(direction, msg));

        const InterruptFrame& frame = mThat.mCxxStackFrames.back();

        if (frame.IsInterruptIncall())
            mThat.EnteredCall();

        mThat.mSawInterruptOutMsg |= frame.IsInterruptOutcall();
    }

    ~CxxStackFrame() {
        mThat.AssertWorkerThread();

        MOZ_ASSERT(!mThat.mCxxStackFrames.empty());

        bool exitingCall = mThat.mCxxStackFrames.back().IsInterruptIncall();
        mThat.mCxxStackFrames.shrinkBy(1);

        bool exitingStack = mThat.mCxxStackFrames.empty();

        // mListener could have gone away if Close() was called while
        // MessageChannel code was still on the stack
        if (!mThat.mListener)
            return;

        if (exitingCall)
            mThat.ExitedCall();

        if (exitingStack)
            mThat.ExitedCxxStack();
    }
private:
    MessageChannel& mThat;

    // Disable harmful methods.
    CxxStackFrame() MOZ_DELETE;
    CxxStackFrame(const CxxStackFrame&) MOZ_DELETE;
    CxxStackFrame& operator=(const CxxStackFrame&) MOZ_DELETE;
};

MessageChannel::MessageChannel(MessageListener *aListener)
  : mListener(aListener->asWeakPtr()),
    mChannelState(ChannelClosed),
    mSide(UnknownSide),
    mLink(nullptr),
    mWorkerLoop(nullptr),
    mChannelErrorTask(nullptr),
    mWorkerLoopID(-1),
    mTimeoutMs(kNoTimeout),
    mInTimeoutSecondHalf(false),
    mNextSeqno(0),
    mPendingSyncReplies(0),
    mPendingUrgentReplies(0),
    mPendingRPCReplies(0),
    mCurrentRPCTransaction(0),
    mDispatchingSyncMessage(false),
    mDispatchingUrgentMessageCount(0),
    mRemoteStackDepthGuess(false),
    mSawInterruptOutMsg(false),
    mAbortOnError(false)
{
    MOZ_COUNT_CTOR(ipc::MessageChannel);

#ifdef OS_WIN
    mTopFrame = nullptr;
#endif

    mDequeueOneTask = new RefCountedTask(NewRunnableMethod(
                                                 this,
                                                 &MessageChannel::OnMaybeDequeueOne));

#ifdef OS_WIN
    mEvent = CreateEventW(nullptr, TRUE, FALSE, nullptr);
    NS_ASSERTION(mEvent, "CreateEvent failed! Nothing is going to work!");
#endif
}

MessageChannel::~MessageChannel()
{
    MOZ_COUNT_DTOR(ipc::MessageChannel);
    IPC_ASSERT(mCxxStackFrames.empty(), "mismatched CxxStackFrame ctor/dtors");
#ifdef OS_WIN
    DebugOnly<BOOL> ok = CloseHandle(mEvent);
    MOZ_ASSERT(ok);
#endif
    Clear();
}

static void
PrintErrorMessage(Side side, const char* channelName, const char* msg)
{
    const char *from = (side == ChildSide)
                       ? "Child"
                       : ((side == ParentSide) ? "Parent" : "Unknown");
    printf_stderr("\n###!!! [%s][%s] Error: %s\n\n", from, channelName, msg);
}

bool
MessageChannel::Connected() const
{
    mMonitor->AssertCurrentThreadOwns();

    // The transport layer allows us to send messages before
    // receiving the "connected" ack from the remote side.
    return (ChannelOpening == mChannelState || ChannelConnected == mChannelState);
}

bool
MessageChannel::CanSend() const
{
    MonitorAutoLock lock(*mMonitor);
    return Connected();
}

void
MessageChannel::Clear()
{
    // Don't clear mWorkerLoopID; we use it in AssertLinkThread() and
    // AssertWorkerThread().
    //
    // Also don't clear mListener.  If we clear it, then sending a message
    // through this channel after it's Clear()'ed can cause this process to
    // crash.
    //
    // In practice, mListener owns the channel, so the channel gets deleted
    // before mListener.  But just to be safe, mListener is a weak pointer.

    mDequeueOneTask->Cancel();

    mWorkerLoop = nullptr;
    delete mLink;
    mLink = nullptr;

    if (mChannelErrorTask) {
        mChannelErrorTask->Cancel();
        mChannelErrorTask = nullptr;
    }
}

bool
MessageChannel::Open(Transport* aTransport, MessageLoop* aIOLoop, Side aSide)
{
    NS_PRECONDITION(!mLink, "Open() called > once");

    mMonitor = new RefCountedMonitor();
    mWorkerLoop = MessageLoop::current();
    mWorkerLoopID = mWorkerLoop->id();

    ProcessLink *link = new ProcessLink(this);
    link->Open(aTransport, aIOLoop, aSide); // :TODO: n.b.: sets mChild
    mLink = link;
    return true;
}

bool
MessageChannel::Open(MessageChannel *aTargetChan, MessageLoop *aTargetLoop, Side aSide)
{
    // Opens a connection to another thread in the same process.

    //  This handshake proceeds as follows:
    //  - Let A be the thread initiating the process (either child or parent)
    //    and B be the other thread.
    //  - A spawns thread for B, obtaining B's message loop
    //  - A creates ProtocolChild and ProtocolParent instances.
    //    Let PA be the one appropriate to A and PB the side for B.
    //  - A invokes PA->Open(PB, ...):
    //    - set state to mChannelOpening
    //    - this will place a work item in B's worker loop (see next bullet)
    //      and then spins until PB->mChannelState becomes mChannelConnected
    //    - meanwhile, on PB's worker loop, the work item is removed and:
    //      - invokes PB->SlaveOpen(PA, ...):
    //        - sets its state and that of PA to Connected
    NS_PRECONDITION(aTargetChan, "Need a target channel");
    NS_PRECONDITION(ChannelClosed == mChannelState, "Not currently closed");

    CommonThreadOpenInit(aTargetChan, aSide);

    Side oppSide = UnknownSide;
    switch(aSide) {
      case ChildSide: oppSide = ParentSide; break;
      case ParentSide: oppSide = ChildSide; break;
      case UnknownSide: break;
    }

    mMonitor = new RefCountedMonitor();

    MonitorAutoLock lock(*mMonitor);
    mChannelState = ChannelOpening;
    aTargetLoop->PostTask(
        FROM_HERE,
        NewRunnableMethod(aTargetChan, &MessageChannel::OnOpenAsSlave, this, oppSide));

    while (ChannelOpening == mChannelState)
        mMonitor->Wait();
    NS_ASSERTION(ChannelConnected == mChannelState, "not connected when awoken");
    return (ChannelConnected == mChannelState);
}

void
MessageChannel::OnOpenAsSlave(MessageChannel *aTargetChan, Side aSide)
{
    // Invoked when the other side has begun the open.
    NS_PRECONDITION(ChannelClosed == mChannelState,
                    "Not currently closed");
    NS_PRECONDITION(ChannelOpening == aTargetChan->mChannelState,
                    "Target channel not in the process of opening");

    CommonThreadOpenInit(aTargetChan, aSide);
    mMonitor = aTargetChan->mMonitor;

    MonitorAutoLock lock(*mMonitor);
    NS_ASSERTION(ChannelOpening == aTargetChan->mChannelState,
                 "Target channel not in the process of opening");
    mChannelState = ChannelConnected;
    aTargetChan->mChannelState = ChannelConnected;
    aTargetChan->mMonitor->Notify();
}

void
MessageChannel::CommonThreadOpenInit(MessageChannel *aTargetChan, Side aSide)
{
    mWorkerLoop = MessageLoop::current();
    mWorkerLoopID = mWorkerLoop->id();
    mLink = new ThreadLink(this, aTargetChan);
    mSide = aSide;
}

bool
MessageChannel::Echo(Message* aMsg)
{
    nsAutoPtr<Message> msg(aMsg);
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();
    if (MSG_ROUTING_NONE == msg->routing_id()) {
        ReportMessageRouteError("MessageChannel::Echo");
        return false;
    }

    MonitorAutoLock lock(*mMonitor);

    if (!Connected()) {
        ReportConnectionError("MessageChannel");
        return false;
    }

    mLink->EchoMessage(msg.forget());
    return true;
}

bool
MessageChannel::Send(Message* aMsg)
{
    CxxStackFrame frame(*this, OUT_MESSAGE, aMsg);

    nsAutoPtr<Message> msg(aMsg);
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();
    if (MSG_ROUTING_NONE == msg->routing_id()) {
        ReportMessageRouteError("MessageChannel::Send");
        return false;
    }

    MonitorAutoLock lock(*mMonitor);
    if (!Connected()) {
        ReportConnectionError("MessageChannel");
        return false;
    }
    mLink->SendMessage(msg.forget());
    return true;
}

bool
MessageChannel::MaybeInterceptSpecialIOMessage(const Message& aMsg)
{
    AssertLinkThread();
    mMonitor->AssertCurrentThreadOwns();

    if (MSG_ROUTING_NONE == aMsg.routing_id() &&
        GOODBYE_MESSAGE_TYPE == aMsg.type())
    {
        // :TODO: Sort out Close() on this side racing with Close() on the
        // other side
        mChannelState = ChannelClosing;
        if (LoggingEnabled()) {
            printf("NOTE: %s process received `Goodbye', closing down\n",
                   (mSide == ChildSide) ? "child" : "parent");
        }
        return true;
    }
    return false;
}

void
MessageChannel::OnMessageReceivedFromLink(const Message& aMsg)
{
    AssertLinkThread();
    mMonitor->AssertCurrentThreadOwns();

    if (MaybeInterceptSpecialIOMessage(aMsg))
        return;

    // Regardless of the Interrupt stack, if we're awaiting a sync or urgent reply,
    // we know that it needs to be immediately handled to unblock us.
    if ((AwaitingSyncReply() && aMsg.is_sync()) ||
        (AwaitingUrgentReply() && aMsg.is_urgent()) ||
        (AwaitingRPCReply() && aMsg.is_rpc()))
    {
        mRecvd = new Message(aMsg);
        NotifyWorkerThread();
        return;
    }

    // Urgent messages cannot be compressed.
    MOZ_ASSERT(!aMsg.compress() || !aMsg.is_urgent());

    bool compress = (aMsg.compress() && !mPending.empty() &&
                     mPending.back().type() == aMsg.type() &&
                     mPending.back().routing_id() == aMsg.routing_id());
    if (compress) {
        // This message type has compression enabled, and the back of the
        // queue was the same message type and routed to the same destination.
        // Replace it with the newer message.
        MOZ_ASSERT(mPending.back().compress());
        mPending.pop_back();
    }

    bool shouldWakeUp = AwaitingInterruptReply() ||
                        // Allow incoming RPCs to be processed inside an urgent message.
                        (AwaitingUrgentReply() && aMsg.is_rpc()) ||
                        // Always process urgent messages while blocked.
                        ((AwaitingSyncReply() || AwaitingRPCReply()) && aMsg.is_urgent());

    // There are four cases we're concerned about, relating to the state of the
    // main thread:
    //
    // (1) We are waiting on a sync|rpc reply - main thread is blocked on the
    //     IPC monitor.
    //   - If the message is high priority, we wake up the main thread to
    //     deliver the message. Otherwise, we leave it in the mPending queue,
    //     posting a task to the main event loop, where it will be processed
    //     once the synchronous reply has been received.
    //
    // (2) We are waiting on an Interrupt reply - main thread is blocked on the
    //     IPC monitor.
    //   - Always notify and wake up the main thread.
    //
    // (3) We are not waiting on a reply.
    //   - We post a task to the main event loop.
    //
    // Note that, we may notify the main thread even though the monitor is not
    // blocked. This is okay, since we always check for pending events before
    // blocking again.

    if (shouldWakeUp && (AwaitingUrgentReply() && aMsg.is_rpc())) {
        // If we're receiving an RPC message while blocked on an urgent message,
        // we must defer any messages that were not sent as part of the child
        // answering the urgent message.
        //
        // We must also be sure that we will not accidentally defer any RPC
        // message that was sent while answering an urgent message. Otherwise,
        // we will deadlock.
        //
        // On the parent side, the current transaction can only transition from 0
        // to an ID, either by us issuing an urgent request while not blocked, or
        // by receiving an RPC request while not blocked. When we unblock, the
        // current transaction is reset to 0.
        //
        // When the child side receives an urgent message, any RPC messages sent
        // before issuing the urgent reply will carry the urgent message's
        // transaction ID.
        //
        // Since AwaitingUrgentReply() implies we are blocked, it also implies
        // that we are within a transaction that will not change until we are
        // completely unblocked (i.e, the transaction has completed).
        if (aMsg.transaction_id() != mCurrentRPCTransaction)
            shouldWakeUp = false;
    }

    if (aMsg.is_urgent()) {
        MOZ_ASSERT(!mPendingUrgentRequest);
        mPendingUrgentRequest = new Message(aMsg);
    } else if (aMsg.is_rpc() && shouldWakeUp) {
        // Only use this slot if we need to wake up for an RPC call. Otherwise
        // we treat it like a normal async or sync message.
        MOZ_ASSERT(!mPendingRPCCall);
        mPendingRPCCall = new Message(aMsg);
    } else {
        mPending.push_back(aMsg);
    }

    if (shouldWakeUp) {
        // Always wake up Interrupt waiters, sync waiters for urgent messages,
        // RPC waiters for urgent messages, and urgent waiters for RPCs in the
        // same transaction.
        NotifyWorkerThread();
    } else {
        // Worker thread is either not blocked on a reply, or this is an
        // incoming Interrupt that raced with outgoing sync, and needs to be
        // deferred to a later event-loop iteration.
        if (!compress) {
            // If we compressed away the previous message, we'll re-use
            // its pending task.
            mWorkerLoop->PostTask(FROM_HERE, new DequeueTask(mDequeueOneTask));
        }
    }
}

bool
MessageChannel::Send(Message* aMsg, Message* aReply)
{
    // Sanity checks.
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();

#ifdef OS_WIN
    SyncStackFrame frame(this, false);
#endif

    CxxStackFrame f(*this, OUT_MESSAGE, aMsg);

    MonitorAutoLock lock(*mMonitor);

    IPC_ASSERT(aMsg->is_sync(), "can only Send() sync messages here");
    IPC_ASSERT(!DispatchingSyncMessage(), "violation of sync handler invariant");
    IPC_ASSERT(!DispatchingUrgentMessage(), "sync messages forbidden while handling urgent message");
    IPC_ASSERT(!AwaitingSyncReply(), "nested sync messages are not supported");

    AutoEnterPendingReply replies(mPendingSyncReplies);
    if (!SendAndWait(aMsg, aReply))
        return false;

    NS_ABORT_IF_FALSE(aReply->is_sync(), "reply is not sync");
    return true;
}

bool
MessageChannel::UrgentCall(Message* aMsg, Message* aReply)
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();
    IPC_ASSERT(mSide == ParentSide, "cannot send urgent requests from child");

#ifdef OS_WIN
    SyncStackFrame frame(this, false);
#endif

    CxxStackFrame f(*this, OUT_MESSAGE, aMsg);

    MonitorAutoLock lock(*mMonitor);

    IPC_ASSERT(!AwaitingInterruptReply(), "urgent calls cannot be issued within Interrupt calls");
    IPC_ASSERT(!AwaitingSyncReply(), "urgent calls cannot be issued within sync sends");

    AutoEnterRPCTransaction transact(this);
    aMsg->set_transaction_id(mCurrentRPCTransaction);

    AutoEnterPendingReply replies(mPendingUrgentReplies);
    if (!SendAndWait(aMsg, aReply))
        return false;

    NS_ABORT_IF_FALSE(aReply->is_urgent(), "reply is not urgent");
    return true;
}

bool
MessageChannel::RPCCall(Message* aMsg, Message* aReply)
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();
    IPC_ASSERT(mSide == ChildSide, "cannot send rpc messages from parent");

#ifdef OS_WIN
    SyncStackFrame frame(this, false);
#endif

    CxxStackFrame f(*this, OUT_MESSAGE, aMsg);

    MonitorAutoLock lock(*mMonitor);

    AutoEnterRPCTransaction transact(this);
    aMsg->set_transaction_id(mCurrentRPCTransaction);

    AutoEnterPendingReply replies(mPendingRPCReplies);
    if (!SendAndWait(aMsg, aReply))
        return false;

    NS_ABORT_IF_FALSE(aReply->is_rpc(), "expected rpc reply");
    return true;
}

bool
MessageChannel::SendAndWait(Message* aMsg, Message* aReply)
{
    mMonitor->AssertCurrentThreadOwns();

    nsAutoPtr<Message> msg(aMsg);

    if (!Connected()) {
        ReportConnectionError("MessageChannel::SendAndWait");
        return false;
    }

    msg->set_seqno(NextSeqno());

    DebugOnly<int32_t> replySeqno = msg->seqno();
    DebugOnly<msgid_t> replyType = msg->type() + 1;

    mLink->SendMessage(msg.forget());

    while (true) {
        // Wait for an event to occur.
        while (true) {
            if (mRecvd || mPendingUrgentRequest || mPendingRPCCall)
                break;

            bool maybeTimedOut = !WaitForSyncNotify();

            if (!Connected()) {
                ReportConnectionError("MessageChannel::SendAndWait");
                return false;
            }

            if (maybeTimedOut && !ShouldContinueFromTimeout())
                return false;
        }

        if (mPendingUrgentRequest && !ProcessPendingUrgentRequest())
            return false;

        if (mPendingRPCCall && !ProcessPendingRPCCall())
            return false;

        if (mRecvd) {
            NS_ABORT_IF_FALSE(mRecvd->is_reply(), "expected reply");

            if (mRecvd->is_reply_error()) {
                mRecvd = nullptr;
                return false;
            }

            NS_ABORT_IF_FALSE(mRecvd->type() == replyType, "wrong reply type");
            NS_ABORT_IF_FALSE(mRecvd->seqno() == replySeqno, "wrong sequence number");

            *aReply = *mRecvd;
            mRecvd = nullptr;
            return true;
        }
    }

    return true;
}

bool
MessageChannel::Call(Message* aMsg, Message* aReply)
{
    if (aMsg->is_urgent())
        return UrgentCall(aMsg, aReply);
    if (aMsg->is_rpc())
        return RPCCall(aMsg, aReply);
    return InterruptCall(aMsg, aReply);
}

bool
MessageChannel::InterruptCall(Message* aMsg, Message* aReply)
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();

#ifdef OS_WIN
    SyncStackFrame frame(this, true);
#endif

    // This must come before MonitorAutoLock, as its destructor acquires the
    // monitor lock.
    CxxStackFrame cxxframe(*this, OUT_MESSAGE, aMsg);

    MonitorAutoLock lock(*mMonitor);
    if (!Connected()) {
        ReportConnectionError("MessageChannel::Call");
        return false;
    }

    // Sanity checks.
    IPC_ASSERT(!AwaitingSyncReply() && !AwaitingUrgentReply(),
               "cannot issue Interrupt call whiel blocked on sync or urgent");
    IPC_ASSERT(!DispatchingSyncMessage() || aMsg->priority() == IPC::Message::PRIORITY_HIGH,
               "violation of sync handler invariant");
    IPC_ASSERT(aMsg->is_interrupt(), "can only Call() Interrupt messages here");


    nsAutoPtr<Message> msg(aMsg);

    msg->set_seqno(NextSeqno());
    msg->set_interrupt_remote_stack_depth_guess(mRemoteStackDepthGuess);
    msg->set_interrupt_local_stack_depth(1 + InterruptStackDepth());
    mInterruptStack.push(*msg);
    mLink->SendMessage(msg.forget());

    while (true) {
        // if a handler invoked by *Dispatch*() spun a nested event
        // loop, and the connection was broken during that loop, we
        // might have already processed the OnError event. if so,
        // trying another loop iteration will be futile because
        // channel state will have been cleared
        if (!Connected()) {
            ReportConnectionError("MessageChannel::InterruptCall");
            return false;
        }

        // Now might be the time to process a message deferred because of race
        // resolution.
        MaybeUndeferIncall();

        // Wait for an event to occur.
        while (!InterruptEventOccurred()) {
            bool maybeTimedOut = !WaitForInterruptNotify();

            // We might have received a "subtly deferred" message in a nested
            // loop that it's now time to process.
            if (InterruptEventOccurred() ||
                (!maybeTimedOut && (!mDeferred.empty() || !mOutOfTurnReplies.empty())))
            {
                break;
            }

            if (maybeTimedOut && !ShouldContinueFromTimeout())
                return false;
        }

        Message recvd;
        MessageMap::iterator it;

        if (mPendingUrgentRequest) {
            recvd = *mPendingUrgentRequest;
            mPendingUrgentRequest = nullptr;
        } else if (mPendingRPCCall) {
            recvd = *mPendingRPCCall;
            mPendingRPCCall = nullptr;
        } else if ((it = mOutOfTurnReplies.find(mInterruptStack.top().seqno()))
                    != mOutOfTurnReplies.end())
        {
            recvd = it->second;
            mOutOfTurnReplies.erase(it);
        } else if (!mPending.empty()) {
            recvd = mPending.front();
            mPending.pop_front();
        } else {
            // because of subtleties with nested event loops, it's possible
            // that we got here and nothing happened.  or, we might have a
            // deferred in-call that needs to be processed.  either way, we
            // won't break the inner while loop again until something new
            // happens.
            continue;
        }

        // If the message is not Interrupt, we can dispatch it as normal.
        if (!recvd.is_interrupt()) {
            // Other side should be blocked.
            IPC_ASSERT(!recvd.is_sync() || mPending.empty(), "other side should be blocked");

            {
                AutoEnterRPCTransaction transaction(this, &recvd);
                MonitorAutoUnlock unlock(*mMonitor);
                CxxStackFrame frame(*this, IN_MESSAGE, &recvd);
                DispatchMessage(recvd);
            }
            if (!Connected()) {
                ReportConnectionError("MessageChannel::DispatchMessage");
                return false;
            }
            continue;
        }

        // If the message is an Interrupt reply, either process it as a reply to our
        // call, or add it to the list of out-of-turn replies we've received.
        if (recvd.is_reply()) {
            IPC_ASSERT(!mInterruptStack.empty(), "invalid Interrupt stack");

            // If this is not a reply the call we've initiated, add it to our
            // out-of-turn replies and keep polling for events.
            {
                const Message &outcall = mInterruptStack.top();

                // Note, In the parent, sequence numbers increase from 0, and
                // in the child, they decrease from 0.
                if ((mSide == ChildSide && recvd.seqno() > outcall.seqno()) ||
                    (mSide != ChildSide && recvd.seqno() < outcall.seqno()))
                {
                    mOutOfTurnReplies[recvd.seqno()] = recvd;
                    continue;
                }

                IPC_ASSERT(recvd.is_reply_error() ||
                           (recvd.type() == (outcall.type() + 1) &&
                            recvd.seqno() == outcall.seqno()),
                           "somebody's misbehavin'", true);
            }

            // We received a reply to our most recent outstanding call. Pop
            // this frame and return the reply.
            mInterruptStack.pop();

            if (!recvd.is_reply_error()) {
                *aReply = recvd;
            }

            // If we have no more pending out calls waiting on replies, then
            // the reply queue should be empty.
            IPC_ASSERT(!mInterruptStack.empty() || mOutOfTurnReplies.empty(),
                       "still have pending replies with no pending out-calls",
                       true);

            return !recvd.is_reply_error();
        }

        // Dispatch an Interrupt in-call. Snapshot the current stack depth while we
        // own the monitor.
        size_t stackDepth = InterruptStackDepth();
        {
            MonitorAutoUnlock unlock(*mMonitor);

            CxxStackFrame frame(*this, IN_MESSAGE, &recvd);
            DispatchInterruptMessage(recvd, stackDepth);
        }
        if (!Connected()) {
            ReportConnectionError("MessageChannel::DispatchInterruptMessage");
            return false;
        }
    }

    return true;
}

bool
MessageChannel::InterruptEventOccurred()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();
    IPC_ASSERT(InterruptStackDepth() > 0, "not in wait loop");

    return (!Connected() ||
            !mPending.empty() ||
            mPendingUrgentRequest ||
            mPendingRPCCall ||
            (!mOutOfTurnReplies.empty() &&
             mOutOfTurnReplies.find(mInterruptStack.top().seqno()) !=
             mOutOfTurnReplies.end()));
}

bool
MessageChannel::ProcessPendingUrgentRequest()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    // Note that it is possible we could have sent a sync message at
    // the same time the parent process sent an urgent message, and
    // therefore mPendingUrgentRequest is set *and* mRecvd is set as
    // well, because the link thread received both before the worker
    // thread woke up.
    //
    // In this case, we process the urgent message first, but we need
    // to save the reply.
    nsAutoPtr<Message> savedReply(mRecvd.forget());

    // We're the child process. We should not be receiving RPC calls.
    IPC_ASSERT(!mPendingRPCCall, "unexpected RPC call");

    nsAutoPtr<Message> recvd(mPendingUrgentRequest.forget());
    {
        // In order to send the parent RPC messages and guarantee it will
        // wake up, we must re-use its transaction.
        AutoEnterRPCTransaction transaction(this, recvd);

        MonitorAutoUnlock unlock(*mMonitor);
        DispatchUrgentMessage(*recvd);
    }
    if (!Connected()) {
        ReportConnectionError("MessageChannel::DispatchUrgentMessage");
        return false;
    }

    // In between having dispatched our reply to the parent process, and
    // re-acquiring the monitor, the parent process could have already
    // processed that reply and sent the reply to our sync message. If so,
    // our saved reply should be empty.
    IPC_ASSERT(!mRecvd || !savedReply, "unknown reply");
    if (!mRecvd)
        mRecvd = savedReply.forget();
    return true;
}

bool
MessageChannel::ProcessPendingRPCCall()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    // See comment above re: mRecvd replies and incoming calls.
    nsAutoPtr<Message> savedReply(mRecvd.forget());

    IPC_ASSERT(!mPendingUrgentRequest, "unexpected urgent message");

    nsAutoPtr<Message> recvd(mPendingRPCCall.forget());
    {
        // If we are not currently in a transaction, this will begin one,
        // and the link thread will not wake us up for any RPC messages not
        // apart of this transaction. If we are already in a transaction,
        // then this will assert that we're still in the same transaction.
        AutoEnterRPCTransaction transaction(this, recvd);

        MonitorAutoUnlock unlock(*mMonitor);
        DispatchRPCMessage(*recvd);
    }
    if (!Connected()) {
        ReportConnectionError("MessageChannel::DispatchRPCMessage");
        return false;
    }

    // In between having dispatched our reply to the parent process, and
    // re-acquiring the monitor, the parent process could have already
    // processed that reply and sent the reply to our sync message. If so,
    // our saved reply should be empty.
    IPC_ASSERT(!mRecvd || !savedReply, "unknown reply");
    if (!mRecvd)
        mRecvd = savedReply.forget();
    return true;
}

bool
MessageChannel::DequeueOne(Message *recvd)
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    if (!Connected()) {
        ReportConnectionError("OnMaybeDequeueOne");
        return false;
    }

    if (mPendingUrgentRequest) {
        *recvd = *mPendingUrgentRequest;
        mPendingUrgentRequest = nullptr;
        return true;
    }

    if (mPendingRPCCall) {
        *recvd = *mPendingRPCCall;
        mPendingRPCCall = nullptr;
        return true;
    }

    if (!mDeferred.empty())
        MaybeUndeferIncall();

    if (mPending.empty())
        return false;

    *recvd = mPending.front();
    mPending.pop_front();
    return true;
}

bool
MessageChannel::OnMaybeDequeueOne()
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();

    Message recvd;

    MonitorAutoLock lock(*mMonitor);
    if (!DequeueOne(&recvd))
        return false;

    if (IsOnCxxStack() && recvd.is_interrupt() && recvd.is_reply()) {
        // We probably just received a reply in a nested loop for an
        // Interrupt call sent before entering that loop.
        mOutOfTurnReplies[recvd.seqno()] = recvd;
        return false;
    }

    {
        // We should not be in a transaction yet if we're not blocked.
        MOZ_ASSERT(mCurrentRPCTransaction == 0);
        AutoEnterRPCTransaction transaction(this, &recvd);

        MonitorAutoUnlock unlock(*mMonitor);

        CxxStackFrame frame(*this, IN_MESSAGE, &recvd);
        DispatchMessage(recvd);
    }
    return true;
}

void
MessageChannel::DispatchMessage(const Message &aMsg)
{
    if (aMsg.is_sync())
        DispatchSyncMessage(aMsg);
    else if (aMsg.is_urgent())
        DispatchUrgentMessage(aMsg);
    else if (aMsg.is_interrupt())
        DispatchInterruptMessage(aMsg, 0);
    else if (aMsg.is_rpc())
        DispatchRPCMessage(aMsg);
    else
        DispatchAsyncMessage(aMsg);
}

void
MessageChannel::DispatchSyncMessage(const Message& aMsg)
{
    AssertWorkerThread();

    Message *reply = nullptr;

    mDispatchingSyncMessage = true;
    Result rv = mListener->OnMessageReceived(aMsg, reply);
    mDispatchingSyncMessage = false;

    if (!MaybeHandleError(rv, "DispatchSyncMessage")) {
        delete reply;
        reply = new Message();
        reply->set_sync();
        reply->set_reply();
        reply->set_reply_error();
    }
    reply->set_seqno(aMsg.seqno());

    MonitorAutoLock lock(*mMonitor);
    if (ChannelConnected == mChannelState)
        mLink->SendMessage(reply);
}

void
MessageChannel::DispatchUrgentMessage(const Message& aMsg)
{
    AssertWorkerThread();
    MOZ_ASSERT(aMsg.is_urgent());

    Message *reply = nullptr;

    mDispatchingUrgentMessageCount++;
    Result rv = mListener->OnCallReceived(aMsg, reply);
    mDispatchingUrgentMessageCount--;

    if (!MaybeHandleError(rv, "DispatchUrgentMessage")) {
        delete reply;
        reply = new Message();
        reply->set_urgent();
        reply->set_reply();
        reply->set_reply_error();
    }
    reply->set_seqno(aMsg.seqno());

    MonitorAutoLock lock(*mMonitor);
    if (ChannelConnected == mChannelState)
        mLink->SendMessage(reply);
}

void
MessageChannel::DispatchRPCMessage(const Message& aMsg)
{
    AssertWorkerThread();
    MOZ_ASSERT(aMsg.is_rpc());

    Message *reply = nullptr;

    if (!MaybeHandleError(mListener->OnCallReceived(aMsg, reply), "DispatchRPCMessage")) {
        delete reply;
        reply = new Message();
        reply->set_rpc();
        reply->set_reply();
        reply->set_reply_error();
    }
    reply->set_seqno(aMsg.seqno());
    
    MonitorAutoLock lock(*mMonitor);
    if (ChannelConnected == mChannelState)
        mLink->SendMessage(reply);
}

void
MessageChannel::DispatchAsyncMessage(const Message& aMsg)
{
    AssertWorkerThread();
    MOZ_ASSERT(!aMsg.is_interrupt() && !aMsg.is_sync() && !aMsg.is_urgent());

    if (aMsg.routing_id() == MSG_ROUTING_NONE) {
        NS_RUNTIMEABORT("unhandled special message!");
    }

    MaybeHandleError(mListener->OnMessageReceived(aMsg), "DispatchAsyncMessage");
}

void
MessageChannel::DispatchInterruptMessage(const Message& aMsg, size_t stackDepth)
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();

    IPC_ASSERT(aMsg.is_interrupt() && !aMsg.is_reply(), "wrong message type");

    // Race detection: see the long comment near mRemoteStackDepthGuess in
    // MessageChannel.h. "Remote" stack depth means our side, and "local" means
    // the other side.
    if (aMsg.interrupt_remote_stack_depth_guess() != RemoteViewOfStackDepth(stackDepth)) {
        // Interrupt in-calls have raced. The winner, if there is one, gets to defer
        // processing of the other side's in-call.
        bool defer;
        const char* winner;
        switch (mListener->MediateInterruptRace((mSide == ChildSide) ? aMsg : mInterruptStack.top(),
                                          (mSide != ChildSide) ? mInterruptStack.top() : aMsg))
        {
          case RIPChildWins:
            winner = "child";
            defer = (mSide == ChildSide);
            break;
          case RIPParentWins:
            winner = "parent";
            defer = (mSide != ChildSide);
            break;
          case RIPError:
            NS_RUNTIMEABORT("NYI: 'Error' Interrupt race policy");
            return;
          default:
            NS_RUNTIMEABORT("not reached");
            return;
        }

        if (LoggingEnabled()) {
            printf_stderr("  (%s: %s won, so we're%sdeferring)\n",
                          (mSide == ChildSide) ? "child" : "parent",
                          winner,
                          defer ? " " : " not ");
        }

        if (defer) {
            // We now know the other side's stack has one more frame
            // than we thought.
            ++mRemoteStackDepthGuess; // decremented in MaybeProcessDeferred()
            mDeferred.push(aMsg);
            return;
        }

        // We "lost" and need to process the other side's in-call. Don't need
        // to fix up the mRemoteStackDepthGuess here, because we're just about
        // to increment it in DispatchCall(), which will make it correct again.
    }

#ifdef OS_WIN
    SyncStackFrame frame(this, true);
#endif

    Message* reply = nullptr;

    ++mRemoteStackDepthGuess;
    Result rv = mListener->OnCallReceived(aMsg, reply);
    --mRemoteStackDepthGuess;

    if (!MaybeHandleError(rv, "DispatchInterruptMessage")) {
        delete reply;
        reply = new Message();
        reply->set_interrupt();
        reply->set_reply();
        reply->set_reply_error();
    }
    reply->set_seqno(aMsg.seqno());

    MonitorAutoLock lock(*mMonitor);
    if (ChannelConnected == mChannelState)
        mLink->SendMessage(reply);
}

void
MessageChannel::MaybeUndeferIncall()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    if (mDeferred.empty())
        return;

    size_t stackDepth = InterruptStackDepth();

    // the other side can only *under*-estimate our actual stack depth
    IPC_ASSERT(mDeferred.top().interrupt_remote_stack_depth_guess() <= stackDepth,
               "fatal logic error");

    if (mDeferred.top().interrupt_remote_stack_depth_guess() < RemoteViewOfStackDepth(stackDepth))
        return;

    // maybe time to process this message
    Message call = mDeferred.top();
    mDeferred.pop();

    // fix up fudge factor we added to account for race
    IPC_ASSERT(0 < mRemoteStackDepthGuess, "fatal logic error");
    --mRemoteStackDepthGuess;

    mPending.push_back(call);
}

void
MessageChannel::FlushPendingInterruptQueue()
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();

    {
        MonitorAutoLock lock(*mMonitor);

        if (mDeferred.empty()) {
            if (mPending.empty())
                return;

            const Message& last = mPending.back();
            if (!last.is_interrupt() || last.is_reply())
                return;
        }
    }

    while (OnMaybeDequeueOne());
}

void
MessageChannel::ExitedCxxStack()
{
    mListener->OnExitedCxxStack();
    if (mSawInterruptOutMsg) {
        MonitorAutoLock lock(*mMonitor);
        // see long comment in OnMaybeDequeueOne()
        EnqueuePendingMessages();
        mSawInterruptOutMsg = false;
    }
}

void
MessageChannel::EnqueuePendingMessages()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    MaybeUndeferIncall();

    for (size_t i = 0; i < mDeferred.size(); ++i) {
        mWorkerLoop->PostTask(FROM_HERE, new DequeueTask(mDequeueOneTask));
    }

    // XXX performance tuning knob: could process all or k pending
    // messages here, rather than enqueuing for later processing

    for (size_t i = 0; i < mPending.size(); ++i) {
        mWorkerLoop->PostTask(FROM_HERE, new DequeueTask(mDequeueOneTask));
    }
}

static inline bool
IsTimeoutExpired(PRIntervalTime aStart, PRIntervalTime aTimeout)
{
    return (aTimeout != PR_INTERVAL_NO_TIMEOUT) &&
           (aTimeout <= (PR_IntervalNow() - aStart));
}

bool
MessageChannel::WaitResponse(bool aWaitTimedOut)
{
    if (aWaitTimedOut) {
        if (mInTimeoutSecondHalf) {
            // We've really timed out this time.
            return false;
        }
        // Try a second time.
        mInTimeoutSecondHalf = true;
    } else {
        mInTimeoutSecondHalf = false;
    }
    return true;
}

#ifndef OS_WIN
bool
MessageChannel::WaitForSyncNotify()
{
    PRIntervalTime timeout = (kNoTimeout == mTimeoutMs) ?
                             PR_INTERVAL_NO_TIMEOUT :
                             PR_MillisecondsToInterval(mTimeoutMs);
    // XXX could optimize away this syscall for "no timeout" case if desired
    PRIntervalTime waitStart = PR_IntervalNow();

    mMonitor->Wait(timeout);

    // If the timeout didn't expire, we know we received an event. The
    // converse is not true.
    return WaitResponse(IsTimeoutExpired(waitStart, timeout));
}

bool
MessageChannel::WaitForInterruptNotify()
{
    return WaitForSyncNotify();
}

void
MessageChannel::NotifyWorkerThread()
{
    mMonitor->Notify();
}
#endif

bool
MessageChannel::ShouldContinueFromTimeout()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    bool cont;
    {
        MonitorAutoUnlock unlock(*mMonitor);
        cont = mListener->OnReplyTimeout();
    }

    static enum { UNKNOWN, NOT_DEBUGGING, DEBUGGING } sDebuggingChildren = UNKNOWN;

    if (sDebuggingChildren == UNKNOWN) {
        sDebuggingChildren = getenv("MOZ_DEBUG_CHILD_PROCESS") ? DEBUGGING : NOT_DEBUGGING;
    }
    if (sDebuggingChildren == DEBUGGING) {
        return true;
    }

    if (!cont) {
        // NB: there's a sublety here.  If parents were allowed to send sync
        // messages to children, then it would be possible for this
        // synchronous close-on-timeout to race with async |OnMessageReceived|
        // tasks arriving from the child, posted to the worker thread's event
        // loop.  This would complicate cleanup of the *Channel.  But since
        // IPDL forbids this (and since it doesn't support children timing out
        // on parents), the parent can only block on interrupt messages to the child,
        // and in that case arriving async messages are enqueued to the interrupt 
        // channel's special queue.  They're then ignored because the channel
        // state changes to ChannelTimeout (i.e. !Connected).
        SynchronouslyClose();
        mChannelState = ChannelTimeout;
    }

    return cont;
}

void
MessageChannel::SetReplyTimeoutMs(int32_t aTimeoutMs)
{
    // Set channel timeout value. Since this is broken up into
    // two period, the minimum timeout value is 2ms.
    AssertWorkerThread();
    mTimeoutMs = (aTimeoutMs <= 0)
                 ? kNoTimeout
                 : (int32_t)ceil((double)aTimeoutMs / 2.0);
}

void
MessageChannel::OnChannelConnected(int32_t peer_id)
{
    mWorkerLoop->PostTask(
        FROM_HERE,
        NewRunnableMethod(this,
                          &MessageChannel::DispatchOnChannelConnected,
                          peer_id));
}

void
MessageChannel::DispatchOnChannelConnected(int32_t peer_pid)
{
    AssertWorkerThread();
    if (mListener)
        mListener->OnChannelConnected(peer_pid);
}

void
MessageChannel::ReportMessageRouteError(const char* channelName) const
{
    PrintErrorMessage(mSide, channelName, "Need a route");
    mListener->OnProcessingError(MsgRouteError);
}

void
MessageChannel::ReportConnectionError(const char* aChannelName) const
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();

    const char* errorMsg = nullptr;
    switch (mChannelState) {
      case ChannelClosed:
        errorMsg = "Closed channel: cannot send/recv";
        break;
      case ChannelOpening:
        errorMsg = "Opening channel: not yet ready for send/recv";
        break;
      case ChannelTimeout:
        errorMsg = "Channel timeout: cannot send/recv";
        break;
      case ChannelClosing:
        errorMsg = "Channel closing: too late to send/recv, messages will be lost";
        break;
      case ChannelError:
        errorMsg = "Channel error: cannot send/recv";
        break;

      default:
        NS_RUNTIMEABORT("unreached");
    }

    PrintErrorMessage(mSide, aChannelName, errorMsg);

    MonitorAutoUnlock unlock(*mMonitor);
    mListener->OnProcessingError(MsgDropped);
}

bool
MessageChannel::MaybeHandleError(Result code, const char* channelName)
{
    if (MsgProcessed == code)
        return true;

    const char* errorMsg = nullptr;
    switch (code) {
      case MsgNotKnown:
        errorMsg = "Unknown message: not processed";
        break;
      case MsgNotAllowed:
        errorMsg = "Message not allowed: cannot be sent/recvd in this state";
        break;
      case MsgPayloadError:
        errorMsg = "Payload error: message could not be deserialized";
        break;
      case MsgProcessingError:
        errorMsg = "Processing error: message was deserialized, but the handler returned false (indicating failure)";
        break;
      case MsgRouteError:
        errorMsg = "Route error: message sent to unknown actor ID";
        break;
      case MsgValueError:
        errorMsg = "Value error: message was deserialized, but contained an illegal value";
        break;

    default:
        NS_RUNTIMEABORT("unknown Result code");
        return false;
    }

    PrintErrorMessage(mSide, channelName, errorMsg);

    mListener->OnProcessingError(code);

    return false;
}

void
MessageChannel::OnChannelErrorFromLink()
{
    AssertLinkThread();
    mMonitor->AssertCurrentThreadOwns();

    if (InterruptStackDepth() > 0)
        NotifyWorkerThread();

    if (AwaitingSyncReply() || AwaitingRPCReply() || AwaitingUrgentReply())
        NotifyWorkerThread();

    if (ChannelClosing != mChannelState) {
        if (mAbortOnError) {
            NS_RUNTIMEABORT("Aborting on channel error.");
        }
        mChannelState = ChannelError;
        mMonitor->Notify();
    }

    PostErrorNotifyTask();
}

void
MessageChannel::NotifyMaybeChannelError()
{
    mMonitor->AssertNotCurrentThreadOwns();

    // TODO sort out Close() on this side racing with Close() on the other side
    if (ChannelClosing == mChannelState) {
        // the channel closed, but we received a "Goodbye" message warning us
        // about it. no worries
        mChannelState = ChannelClosed;
        NotifyChannelClosed();
        return;
    }

    // Oops, error!  Let the listener know about it.
    mChannelState = ChannelError;
    mListener->OnChannelError();
    Clear();
}

void
MessageChannel::OnNotifyMaybeChannelError()
{
    AssertWorkerThread();
    mMonitor->AssertNotCurrentThreadOwns();

    mChannelErrorTask = nullptr;

    // OnChannelError holds mMonitor when it posts this task and this
    // task cannot be allowed to run until OnChannelError has
    // exited. We enforce that order by grabbing the mutex here which
    // should only continue once OnChannelError has completed.
    {
        MonitorAutoLock lock(*mMonitor);
        // nothing to do here
    }

    if (IsOnCxxStack()) {
        mChannelErrorTask =
            NewRunnableMethod(this, &MessageChannel::OnNotifyMaybeChannelError);
        // 10 ms delay is completely arbitrary
        mWorkerLoop->PostDelayedTask(FROM_HERE, mChannelErrorTask, 10);
        return;
    }

    NotifyMaybeChannelError();
}

void
MessageChannel::PostErrorNotifyTask()
{
    mMonitor->AssertCurrentThreadOwns();

    if (mChannelErrorTask)
        return;

    // This must be the last code that runs on this thread!
    mChannelErrorTask =
        NewRunnableMethod(this, &MessageChannel::OnNotifyMaybeChannelError);
    mWorkerLoop->PostTask(FROM_HERE, mChannelErrorTask);
}

// Special async message.
class GoodbyeMessage : public IPC::Message
{
public:
    GoodbyeMessage() :
        IPC::Message(MSG_ROUTING_NONE, GOODBYE_MESSAGE_TYPE, PRIORITY_NORMAL)
    {
    }
    static bool Read(const Message* msg) {
        return true;
    }
    void Log(const std::string& aPrefix, FILE* aOutf) const {
        fputs("(special `Goodbye' message)", aOutf);
    }
};

void
MessageChannel::SynchronouslyClose()
{
    AssertWorkerThread();
    mMonitor->AssertCurrentThreadOwns();
    mLink->SendClose();
    while (ChannelClosed != mChannelState)
        mMonitor->Wait();
}

void
MessageChannel::CloseWithError()
{
    AssertWorkerThread();

    MonitorAutoLock lock(*mMonitor);
    if (ChannelConnected != mChannelState) {
        return;
    }
    SynchronouslyClose();
    mChannelState = ChannelError;
    PostErrorNotifyTask();
}

void
MessageChannel::Close()
{
    AssertWorkerThread();

    {
        MonitorAutoLock lock(*mMonitor);

        if (ChannelError == mChannelState || ChannelTimeout == mChannelState) {
            // See bug 538586: if the listener gets deleted while the
            // IO thread's NotifyChannelError event is still enqueued
            // and subsequently deletes us, then the error event will
            // also be deleted and the listener will never be notified
            // of the channel error.
            if (mListener) {
                MonitorAutoUnlock unlock(*mMonitor);
                NotifyMaybeChannelError();
            }
            return;
        }

        if (ChannelOpening == mChannelState) {
            // Mimic CloseWithError().
            SynchronouslyClose();
            mChannelState = ChannelError;
            PostErrorNotifyTask();
            return;
        }

        if (ChannelConnected != mChannelState) {
            // XXX be strict about this until there's a compelling reason
            // to relax
            NS_RUNTIMEABORT("Close() called on closed channel!");
        }

        // notify the other side that we're about to close our socket
        mLink->SendMessage(new GoodbyeMessage());
        SynchronouslyClose();
    }

    NotifyChannelClosed();
}

void
MessageChannel::NotifyChannelClosed()
{
    mMonitor->AssertNotCurrentThreadOwns();

    if (ChannelClosed != mChannelState)
        NS_RUNTIMEABORT("channel should have been closed!");

    // OK, the IO thread just closed the channel normally.  Let the
    // listener know about it.
    mListener->OnChannelClose();

    Clear();
}

void
MessageChannel::DebugAbort(const char* file, int line, const char* cond,
                           const char* why,
                           bool reply) const
{
    printf_stderr("###!!! [MessageChannel][%s][%s:%d] "
                  "Assertion (%s) failed.  %s %s\n",
                  mSide == ChildSide ? "Child" : "Parent",
                  file, line, cond,
                  why,
                  reply ? "(reply)" : "");
    // technically we need the mutex for this, but we're dying anyway
    DumpInterruptStack("  ");
    printf_stderr("  remote Interrupt stack guess: %lu\n",
                  mRemoteStackDepthGuess);
    printf_stderr("  deferred stack size: %lu\n",
                  mDeferred.size());
    printf_stderr("  out-of-turn Interrupt replies stack size: %lu\n",
                  mOutOfTurnReplies.size());
    printf_stderr("  Pending queue size: %lu, front to back:\n",
                  mPending.size());

    MessageQueue pending = mPending;
    while (!pending.empty()) {
        printf_stderr("    [ %s%s ]\n",
                      pending.front().is_interrupt() ? "intr" :
                      (pending.front().is_sync() ? "sync" : "async"),
                      pending.front().is_reply() ? "reply" : "");
        pending.pop_front();
    }

    NS_RUNTIMEABORT(why);
}

void
MessageChannel::DumpInterruptStack(const char* const pfx) const
{
    NS_WARN_IF_FALSE(MessageLoop::current() != mWorkerLoop,
                     "The worker thread had better be paused in a debugger!");

    printf_stderr("%sMessageChannel 'backtrace':\n", pfx);

    // print a python-style backtrace, first frame to last
    for (uint32_t i = 0; i < mCxxStackFrames.length(); ++i) {
        int32_t id;
        const char* dir, *sems, *name;
        mCxxStackFrames[i].Describe(&id, &dir, &sems, &name);

        printf_stderr("%s[(%u) %s %s %s(actor=%d) ]\n", pfx,
                      i, dir, sems, name, id);
    }
}

} // ipc
} // mozilla