flang/runtime/unit.cpp

   1 //===-- runtime/unit.cpp --------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "unit.h"
  10 #include "io-error.h"
  11 #include "lock.h"
  12 #include "tools.h"
  13 #include "unit-map.h"
  14 #include <cstdio>
  15 #include <limits>
  16 #include <utility>
  17
  18 namespace Fortran::runtime::io {
  19
  20 // The per-unit data structures are created on demand so that Fortran I/O
  21 // should work without a Fortran main program.
  22 static Lock unitMapLock;
  23 static UnitMap *unitMap{nullptr};
  24 static ExternalFileUnit *defaultInput{nullptr}; // unit 5
  25 static ExternalFileUnit *defaultOutput{nullptr}; // unit 6
  26 static ExternalFileUnit *errorOutput{nullptr}; // unit 0 extension
  27
  28 void FlushOutputOnCrash(const Terminator &terminator) {
  29   if (!defaultOutput && !errorOutput) {
  30     return;
  31   }
  32   IoErrorHandler handler{terminator};
  33   handler.HasIoStat(); // prevent nested crash if flush has error
  34   CriticalSection critical{unitMapLock};
  35   if (defaultOutput) {
  36     defaultOutput->FlushOutput(handler);
  37   }
  38   if (errorOutput) {
  39     errorOutput->FlushOutput(handler);
  40   }
  41 }
  42
  43 ExternalFileUnit *ExternalFileUnit::LookUp(int unit) {
  44   return GetUnitMap().LookUp(unit);
  45 }
  46
  47 ExternalFileUnit *ExternalFileUnit::LookUpOrCreate(
  48     int unit, const Terminator &terminator, bool &wasExtant) {
  49   return GetUnitMap().LookUpOrCreate(unit, terminator, wasExtant);
  50 }
  51
  52 ExternalFileUnit *ExternalFileUnit::LookUpOrCreateAnonymous(int unit,
  53     Direction dir, std::optional<bool> isUnformatted,
  54     const Terminator &terminator) {
  55   bool exists{false};
  56   ExternalFileUnit *result{
  57       GetUnitMap().LookUpOrCreate(unit, terminator, exists)};
  58   if (result && !exists) {
  59     IoErrorHandler handler{terminator};
  60     result->OpenAnonymousUnit(
  61         dir == Direction::Input ? OpenStatus::Unknown : OpenStatus::Replace,
  62         Action::ReadWrite, Position::Rewind, Convert::Unknown, handler);
  63     result->isUnformatted = isUnformatted;
  64   }
  65   return result;
  66 }
  67
  68 ExternalFileUnit *ExternalFileUnit::LookUp(
  69     const char *path, std::size_t pathLen) {
  70   return GetUnitMap().LookUp(path, pathLen);
  71 }
  72
  73 ExternalFileUnit &ExternalFileUnit::CreateNew(
  74     int unit, const Terminator &terminator) {
  75   bool wasExtant{false};
  76   ExternalFileUnit *result{
  77       GetUnitMap().LookUpOrCreate(unit, terminator, wasExtant)};
  78   RUNTIME_CHECK(terminator, result && !wasExtant);
  79   return *result;
  80 }
  81
  82 ExternalFileUnit *ExternalFileUnit::LookUpForClose(int unit) {
  83   return GetUnitMap().LookUpForClose(unit);
  84 }
  85
  86 ExternalFileUnit &ExternalFileUnit::NewUnit(
  87     const Terminator &terminator, bool forChildIo) {
  88   ExternalFileUnit &unit{GetUnitMap().NewUnit(terminator)};
  89   unit.createdForInternalChildIo_ = forChildIo;
  90   return unit;
  91 }
  92
  93 bool ExternalFileUnit::OpenUnit(std::optional<OpenStatus> status,
  94     std::optional<Action> action, Position position, OwningPtr<char> &&newPath,
  95     std::size_t newPathLength, Convert convert, IoErrorHandler &handler) {
  96   if (convert == Convert::Unknown) {
  97     convert = executionEnvironment.conversion;
  98   }
  99   swapEndianness_ = convert == Convert::Swap ||
 100       (convert == Convert::LittleEndian && !isHostLittleEndian) ||
 101       (convert == Convert::BigEndian && isHostLittleEndian);
 102   bool impliedClose{false};
 103   if (IsConnected()) {
 104     bool isSamePath{newPath.get() && path() && pathLength() == newPathLength &&
 105         std::memcmp(path(), newPath.get(), newPathLength) == 0};
 106     if (status && *status != OpenStatus::Old && isSamePath) {
 107       handler.SignalError("OPEN statement for connected unit may not have "
 108                           "explicit STATUS= other than 'OLD'");
 109       return impliedClose;
 110     }
 111     if (!newPath.get() || isSamePath) {
 112       // OPEN of existing unit, STATUS='OLD' or unspecified, not new FILE=
 113       newPath.reset();
 114       return impliedClose;
 115     }
 116     // Otherwise, OPEN on open unit with new FILE= implies CLOSE
 117     DoImpliedEndfile(handler);
 118     FlushOutput(handler);
 119     TruncateFrame(0, handler);
 120     Close(CloseStatus::Keep, handler);
 121     impliedClose = true;
 122   }
 123   if (newPath.get() && newPathLength > 0) {
 124     if (const auto *already{
 125             GetUnitMap().LookUp(newPath.get(), newPathLength)}) {
 126       handler.SignalError(IostatOpenAlreadyConnected,
 127           "OPEN(UNIT=%d,FILE='%.*s'): file is already connected to unit %d",
 128           unitNumber_, static_cast<int>(newPathLength), newPath.get(),
 129           already->unitNumber_);
 130       return impliedClose;
 131     }
 132   }
 133   set_path(std::move(newPath), newPathLength);
 134   Open(status.value_or(OpenStatus::Unknown), action, position, handler);
 135   auto totalBytes{knownSize()};
 136   if (access == Access::Direct) {
 137     if (!openRecl) {
 138       handler.SignalError(IostatOpenBadRecl,
 139           "OPEN(UNIT=%d,ACCESS='DIRECT'): record length is not known",
 140           unitNumber());
 141     } else if (*openRecl <= 0) {
 142       handler.SignalError(IostatOpenBadRecl,
 143           "OPEN(UNIT=%d,ACCESS='DIRECT',RECL=%jd): record length is invalid",
 144           unitNumber(), static_cast<std::intmax_t>(*openRecl));
 145     } else if (totalBytes && (*totalBytes % *openRecl != 0)) {
 146       handler.SignalError(IostatOpenBadRecl,
 147           "OPEN(UNIT=%d,ACCESS='DIRECT',RECL=%jd): record length is not an "
 148           "even divisor of the file size %jd",
 149           unitNumber(), static_cast<std::intmax_t>(*openRecl),
 150           static_cast<std::intmax_t>(*totalBytes));
 151     }
 152     recordLength = openRecl;
 153   }
 154   endfileRecordNumber.reset();
 155   currentRecordNumber = 1;
 156   if (totalBytes && access == Access::Direct && openRecl.value_or(0) > 0) {
 157     endfileRecordNumber = 1 + (*totalBytes / *openRecl);
 158   }
 159   if (position == Position::Append) {
 160     if (totalBytes) {
 161       frameOffsetInFile_ = *totalBytes;
 162     }
 163     if (access != Access::Stream) {
 164       if (!endfileRecordNumber) {
 165         // Fake it so that we can backspace relative from the end
 166         endfileRecordNumber = std::numeric_limits<std::int64_t>::max() - 2;
 167       }
 168       currentRecordNumber = *endfileRecordNumber;
 169     }
 170   }
 171   return impliedClose;
 172 }
 173
 174 void ExternalFileUnit::OpenAnonymousUnit(std::optional<OpenStatus> status,
 175     std::optional<Action> action, Position position, Convert convert,
 176     IoErrorHandler &handler) {
 177   // I/O to an unconnected unit reads/creates a local file, e.g. fort.7
 178   std::size_t pathMaxLen{32};
 179   auto path{SizedNew<char>{handler}(pathMaxLen)};
 180   std::snprintf(path.get(), pathMaxLen, "fort.%d", unitNumber_);
 181   OpenUnit(status, action, position, std::move(path), std::strlen(path.get()),
 182       convert, handler);
 183 }
 184
 185 void ExternalFileUnit::CloseUnit(CloseStatus status, IoErrorHandler &handler) {
 186   DoImpliedEndfile(handler);
 187   FlushOutput(handler);
 188   Close(status, handler);
 189 }
 190
 191 void ExternalFileUnit::DestroyClosed() {
 192   GetUnitMap().DestroyClosed(*this); // destroys *this
 193 }
 194
 195 Iostat ExternalFileUnit::SetDirection(Direction direction) {
 196   if (direction == Direction::Input) {
 197     if (mayRead()) {
 198       direction_ = Direction::Input;
 199       return IostatOk;
 200     } else {
 201       return IostatReadFromWriteOnly;
 202     }
 203   } else {
 204     if (mayWrite()) {
 205       direction_ = Direction::Output;
 206       return IostatOk;
 207     } else {
 208       return IostatWriteToReadOnly;
 209     }
 210   }
 211 }
 212
 213 UnitMap &ExternalFileUnit::CreateUnitMap() {
 214   Terminator terminator{__FILE__, __LINE__};
 215   IoErrorHandler handler{terminator};
 216   UnitMap &newUnitMap{*New<UnitMap>{terminator}().release()};
 217
 218   bool wasExtant{false};
 219   ExternalFileUnit &out{*newUnitMap.LookUpOrCreate(6, terminator, wasExtant)};
 220   RUNTIME_CHECK(terminator, !wasExtant);
 221   out.Predefine(1);
 222   handler.SignalError(out.SetDirection(Direction::Output));
 223   out.isUnformatted = false;
 224   defaultOutput = &out;
 225
 226   ExternalFileUnit &in{*newUnitMap.LookUpOrCreate(5, terminator, wasExtant)};
 227   RUNTIME_CHECK(terminator, !wasExtant);
 228   in.Predefine(0);
 229   handler.SignalError(in.SetDirection(Direction::Input));
 230   in.isUnformatted = false;
 231   defaultInput = &in;
 232
 233   ExternalFileUnit &error{*newUnitMap.LookUpOrCreate(0, terminator, wasExtant)};
 234   RUNTIME_CHECK(terminator, !wasExtant);
 235   error.Predefine(2);
 236   handler.SignalError(error.SetDirection(Direction::Output));
 237   error.isUnformatted = false;
 238   errorOutput = &error;
 239
 240   return newUnitMap;
 241 }
 242
 243 // A back-up atexit() handler for programs that don't terminate with a main
 244 // program END or a STOP statement or other Fortran-initiated program shutdown,
 245 // such as programs with a C main() that terminate normally.  It flushes all
 246 // external I/O units.  It is registered once the first time that any external
 247 // I/O is attempted.
 248 static void CloseAllExternalUnits() {
 249   IoErrorHandler handler{"Fortran program termination"};
 250   ExternalFileUnit::CloseAll(handler);
 251 }
 252
 253 UnitMap &ExternalFileUnit::GetUnitMap() {
 254   if (unitMap) {
 255     return *unitMap;
 256   }
 257   {
 258     CriticalSection critical{unitMapLock};
 259     if (unitMap) {
 260       return *unitMap;
 261     }
 262     unitMap = &CreateUnitMap();
 263   }
 264   std::atexit(CloseAllExternalUnits);
 265   return *unitMap;
 266 }
 267
 268 void ExternalFileUnit::CloseAll(IoErrorHandler &handler) {
 269   CriticalSection critical{unitMapLock};
 270   if (unitMap) {
 271     unitMap->CloseAll(handler);
 272     FreeMemoryAndNullify(unitMap);
 273   }
 274   defaultOutput = nullptr;
 275   defaultInput = nullptr;
 276   errorOutput = nullptr;
 277 }
 278
 279 void ExternalFileUnit::FlushAll(IoErrorHandler &handler) {
 280   CriticalSection critical{unitMapLock};
 281   if (unitMap) {
 282     unitMap->FlushAll(handler);
 283   }
 284 }
 285
 286 static inline void SwapEndianness(
 287     char *data, std::size_t bytes, std::size_t elementBytes) {
 288   if (elementBytes > 1) {
 289     auto half{elementBytes >> 1};
 290     for (std::size_t j{0}; j + elementBytes <= bytes; j += elementBytes) {
 291       for (std::size_t k{0}; k < half; ++k) {
 292         std::swap(data[j + k], data[j + elementBytes - 1 - k]);
 293       }
 294     }
 295   }
 296 }
 297
 298 bool ExternalFileUnit::Emit(const char *data, std::size_t bytes,
 299     std::size_t elementBytes, IoErrorHandler &handler) {
 300   auto furthestAfter{std::max(furthestPositionInRecord,
 301       positionInRecord + static_cast<std::int64_t>(bytes))};
 302   if (openRecl) {
 303     // Check for fixed-length record overrun, but allow for
 304     // sequential record termination.
 305     int extra{0};
 306     int header{0};
 307     if (access == Access::Sequential) {
 308       if (isUnformatted.value_or(false)) {
 309         // record header + footer
 310         header = static_cast<int>(sizeof(std::uint32_t));
 311         extra = 2 * header;
 312       } else {
 313 #ifdef _WIN32
 314         if (!isWindowsTextFile()) {
 315           ++extra; // carriage return (CR)
 316         }
 317 #endif
 318         ++extra; // newline (LF)
 319       }
 320     }
 321     if (furthestAfter > extra + *openRecl) {
 322       handler.SignalError(IostatRecordWriteOverrun,
 323           "Attempt to write %zd bytes to position %jd in a fixed-size record "
 324           "of %jd bytes",
 325           bytes, static_cast<std::intmax_t>(positionInRecord - header),
 326           static_cast<std::intmax_t>(*openRecl));
 327       return false;
 328     }
 329   }
 330   if (recordLength) {
 331     // It is possible for recordLength to have a value now for a
 332     // variable-length output record if the previous operation
 333     // was a BACKSPACE or non advancing input statement.
 334     recordLength.reset();
 335     beganReadingRecord_ = false;
 336   }
 337   if (IsAfterEndfile()) {
 338     handler.SignalError(IostatWriteAfterEndfile);
 339     return false;
 340   }
 341   CheckDirectAccess(handler);
 342   WriteFrame(frameOffsetInFile_, recordOffsetInFrame_ + furthestAfter, handler);
 343   if (positionInRecord > furthestPositionInRecord) {
 344     std::memset(Frame() + recordOffsetInFrame_ + furthestPositionInRecord, ' ',
 345         positionInRecord - furthestPositionInRecord);
 346   }
 347   char *to{Frame() + recordOffsetInFrame_ + positionInRecord};
 348   std::memcpy(to, data, bytes);
 349   if (swapEndianness_) {
 350     SwapEndianness(to, bytes, elementBytes);
 351   }
 352   positionInRecord += bytes;
 353   furthestPositionInRecord = furthestAfter;
 354   return true;
 355 }
 356
 357 bool ExternalFileUnit::Receive(char *data, std::size_t bytes,
 358     std::size_t elementBytes, IoErrorHandler &handler) {
 359   RUNTIME_CHECK(handler, direction_ == Direction::Input);
 360   auto furthestAfter{std::max(furthestPositionInRecord,
 361       positionInRecord + static_cast<std::int64_t>(bytes))};
 362   if (furthestAfter > recordLength.value_or(furthestAfter)) {
 363     handler.SignalError(IostatRecordReadOverrun,
 364         "Attempt to read %zd bytes at position %jd in a record of %jd bytes",
 365         bytes, static_cast<std::intmax_t>(positionInRecord),
 366         static_cast<std::intmax_t>(*recordLength));
 367     return false;
 368   }
 369   auto need{recordOffsetInFrame_ + furthestAfter};
 370   auto got{ReadFrame(frameOffsetInFile_, need, handler)};
 371   if (got >= need) {
 372     std::memcpy(data, Frame() + recordOffsetInFrame_ + positionInRecord, bytes);
 373     if (swapEndianness_) {
 374       SwapEndianness(data, bytes, elementBytes);
 375     }
 376     positionInRecord += bytes;
 377     furthestPositionInRecord = furthestAfter;
 378     return true;
 379   } else {
 380     HitEndOnRead(handler);
 381     return false;
 382   }
 383 }
 384
 385 std::size_t ExternalFileUnit::GetNextInputBytes(
 386     const char *&p, IoErrorHandler &handler) {
 387   RUNTIME_CHECK(handler, direction_ == Direction::Input);
 388   std::size_t length{1};
 389   if (auto recl{EffectiveRecordLength()}) {
 390     if (positionInRecord < *recl) {
 391       length = *recl - positionInRecord;
 392     } else {
 393       p = nullptr;
 394       return 0;
 395     }
 396   }
 397   p = FrameNextInput(handler, length);
 398   return p ? length : 0;
 399 }
 400
 401 const char *ExternalFileUnit::FrameNextInput(
 402     IoErrorHandler &handler, std::size_t bytes) {
 403   RUNTIME_CHECK(handler, isUnformatted.has_value() && !*isUnformatted);
 404   if (static_cast<std::int64_t>(positionInRecord + bytes) <=
 405       recordLength.value_or(positionInRecord + bytes)) {
 406     auto at{recordOffsetInFrame_ + positionInRecord};
 407     auto need{static_cast<std::size_t>(at + bytes)};
 408     auto got{ReadFrame(frameOffsetInFile_, need, handler)};
 409     SetVariableFormattedRecordLength();
 410     if (got >= need) {
 411       return Frame() + at;
 412     }
 413     HitEndOnRead(handler);
 414   }
 415   return nullptr;
 416 }
 417
 418 bool ExternalFileUnit::SetVariableFormattedRecordLength() {
 419   if (recordLength || access == Access::Direct) {
 420     return true;
 421   } else if (FrameLength() > recordOffsetInFrame_) {
 422     const char *record{Frame() + recordOffsetInFrame_};
 423     std::size_t bytes{FrameLength() - recordOffsetInFrame_};
 424     if (const char *nl{FindCharacter(record, '\n', bytes)}) {
 425       recordLength = nl - record;
 426       if (*recordLength > 0 && record[*recordLength - 1] == '\r') {
 427         --*recordLength;
 428       }
 429       return true;
 430     }
 431   }
 432   return false;
 433 }
 434
 435 bool ExternalFileUnit::BeginReadingRecord(IoErrorHandler &handler) {
 436   RUNTIME_CHECK(handler, direction_ == Direction::Input);
 437   if (!beganReadingRecord_) {
 438     beganReadingRecord_ = true;
 439     if (access == Access::Direct) {
 440       CheckDirectAccess(handler);
 441       auto need{static_cast<std::size_t>(recordOffsetInFrame_ + *openRecl)};
 442       auto got{ReadFrame(frameOffsetInFile_, need, handler)};
 443       if (got >= need) {
 444         recordLength = openRecl;
 445       } else {
 446         recordLength.reset();
 447         HitEndOnRead(handler);
 448       }
 449     } else {
 450       recordLength.reset();
 451       if (IsAtEOF()) {
 452         handler.SignalEnd();
 453       } else {
 454         RUNTIME_CHECK(handler, isUnformatted.has_value());
 455         if (*isUnformatted) {
 456           if (access == Access::Sequential) {
 457             BeginSequentialVariableUnformattedInputRecord(handler);
 458           }
 459         } else { // formatted sequential or stream
 460           BeginVariableFormattedInputRecord(handler);
 461         }
 462       }
 463     }
 464   }
 465   RUNTIME_CHECK(handler,
 466       recordLength.has_value() || !IsRecordFile() || handler.InError());
 467   return !handler.InError();
 468 }
 469
 470 void ExternalFileUnit::FinishReadingRecord(IoErrorHandler &handler) {
 471   RUNTIME_CHECK(handler, direction_ == Direction::Input && beganReadingRecord_);
 472   beganReadingRecord_ = false;
 473   if (handler.GetIoStat() == IostatEnd ||
 474       (IsRecordFile() && !recordLength.has_value())) {
 475     // Avoid bogus crashes in END/ERR circumstances; but
 476     // still increment the current record number so that
 477     // an attempted read of an endfile record, followed by
 478     // a BACKSPACE, will still be at EOF.
 479     ++currentRecordNumber;
 480   } else if (IsRecordFile()) {
 481     recordOffsetInFrame_ += *recordLength;
 482     if (access != Access::Direct) {
 483       RUNTIME_CHECK(handler, isUnformatted.has_value());
 484       recordLength.reset();
 485       if (isUnformatted.value_or(false)) {
 486         // Retain footer in frame for more efficient BACKSPACE
 487         frameOffsetInFile_ += recordOffsetInFrame_;
 488         recordOffsetInFrame_ = sizeof(std::uint32_t);
 489       } else { // formatted
 490         if (FrameLength() > recordOffsetInFrame_ &&
 491             Frame()[recordOffsetInFrame_] == '\r') {
 492           ++recordOffsetInFrame_;
 493         }
 494         if (FrameLength() > recordOffsetInFrame_ &&
 495             Frame()[recordOffsetInFrame_] == '\n') {
 496           ++recordOffsetInFrame_;
 497         }
 498         if (!pinnedFrame || mayPosition()) {
 499           frameOffsetInFile_ += recordOffsetInFrame_;
 500           recordOffsetInFrame_ = 0;
 501         }
 502       }
 503     }
 504     ++currentRecordNumber;
 505   } else { // unformatted stream
 506     furthestPositionInRecord =
 507         std::max(furthestPositionInRecord, positionInRecord);
 508     frameOffsetInFile_ += recordOffsetInFrame_ + furthestPositionInRecord;
 509   }
 510   BeginRecord();
 511 }
 512
 513 bool ExternalFileUnit::AdvanceRecord(IoErrorHandler &handler) {
 514   if (direction_ == Direction::Input) {
 515     FinishReadingRecord(handler);
 516     return BeginReadingRecord(handler);
 517   } else { // Direction::Output
 518     bool ok{true};
 519     RUNTIME_CHECK(handler, isUnformatted.has_value());
 520     positionInRecord = furthestPositionInRecord;
 521     if (access == Access::Direct) {
 522       if (furthestPositionInRecord <
 523           openRecl.value_or(furthestPositionInRecord)) {
 524         // Pad remainder of fixed length record
 525         WriteFrame(
 526             frameOffsetInFile_, recordOffsetInFrame_ + *openRecl, handler);
 527         std::memset(Frame() + recordOffsetInFrame_ + furthestPositionInRecord,
 528             isUnformatted.value_or(false) ? 0 : ' ',
 529             *openRecl - furthestPositionInRecord);
 530         furthestPositionInRecord = *openRecl;
 531       }
 532     } else if (*isUnformatted) {
 533       if (access == Access::Sequential) {
 534         // Append the length of a sequential unformatted variable-length record
 535         // as its footer, then overwrite the reserved first four bytes of the
 536         // record with its length as its header.  These four bytes were skipped
 537         // over in BeginUnformattedIO<Output>().
 538         // TODO: Break very large records up into subrecords with negative
 539         // headers &/or footers
 540         std::uint32_t length;
 541         length = furthestPositionInRecord - sizeof length;
 542         ok = ok &&
 543             Emit(reinterpret_cast<const char *>(&length), sizeof length,
 544                 sizeof length, handler);
 545         positionInRecord = 0;
 546         ok = ok &&
 547             Emit(reinterpret_cast<const char *>(&length), sizeof length,
 548                 sizeof length, handler);
 549       } else {
 550         // Unformatted stream: nothing to do
 551       }
 552     } else if (handler.GetIoStat() != IostatOk &&
 553         furthestPositionInRecord == 0) {
 554       // Error in formatted variable length record, and no output yet; do
 555       // nothing, like most other Fortran compilers do.
 556       return true;
 557     } else {
 558       // Terminate formatted variable length record
 559       const char *lineEnding{"\n"};
 560       std::size_t lineEndingBytes{1};
 561 #ifdef _WIN32
 562       if (!isWindowsTextFile()) {
 563         lineEnding = "\r\n";
 564         lineEndingBytes = 2;
 565       }
 566 #endif
 567       ok = ok && Emit(lineEnding, lineEndingBytes, 1, handler);
 568     }
 569     leftTabLimit.reset();
 570     if (IsAfterEndfile()) {
 571       return false;
 572     }
 573     CommitWrites();
 574     ++currentRecordNumber;
 575     if (access != Access::Direct) {
 576       impliedEndfile_ = IsRecordFile();
 577       if (IsAtEOF()) {
 578         endfileRecordNumber.reset();
 579       }
 580     }
 581     return ok;
 582   }
 583 }
 584
 585 void ExternalFileUnit::BackspaceRecord(IoErrorHandler &handler) {
 586   if (access == Access::Direct || !IsRecordFile()) {
 587     handler.SignalError(IostatBackspaceNonSequential,
 588         "BACKSPACE(UNIT=%d) on direct-access file or unformatted stream",
 589         unitNumber());
 590   } else {
 591     if (IsAfterEndfile()) {
 592       // BACKSPACE after explicit ENDFILE
 593       currentRecordNumber = *endfileRecordNumber;
 594     } else if (leftTabLimit) {
 595       // BACKSPACE after non-advancing I/O
 596       leftTabLimit.reset();
 597     } else {
 598       DoImpliedEndfile(handler);
 599       if (frameOffsetInFile_ + recordOffsetInFrame_ > 0) {
 600         --currentRecordNumber;
 601         if (openRecl && access == Access::Direct) {
 602           BackspaceFixedRecord(handler);
 603         } else {
 604           RUNTIME_CHECK(handler, isUnformatted.has_value());
 605           if (isUnformatted.value_or(false)) {
 606             BackspaceVariableUnformattedRecord(handler);
 607           } else {
 608             BackspaceVariableFormattedRecord(handler);
 609           }
 610         }
 611       }
 612     }
 613     BeginRecord();
 614   }
 615 }
 616
 617 void ExternalFileUnit::FlushOutput(IoErrorHandler &handler) {
 618   if (!mayPosition()) {
 619     auto frameAt{FrameAt()};
 620     if (frameOffsetInFile_ >= frameAt &&
 621         frameOffsetInFile_ <
 622             static_cast<std::int64_t>(frameAt + FrameLength())) {
 623       // A Flush() that's about to happen to a non-positionable file
 624       // needs to advance frameOffsetInFile_ to prevent attempts at
 625       // impossible seeks
 626       CommitWrites();
 627       leftTabLimit.reset();
 628     }
 629   }
 630   Flush(handler);
 631 }
 632
 633 void ExternalFileUnit::FlushIfTerminal(IoErrorHandler &handler) {
 634   if (isTerminal()) {
 635     FlushOutput(handler);
 636   }
 637 }
 638
 639 void ExternalFileUnit::Endfile(IoErrorHandler &handler) {
 640   if (access == Access::Direct) {
 641     handler.SignalError(IostatEndfileDirect,
 642         "ENDFILE(UNIT=%d) on direct-access file", unitNumber());
 643   } else if (!mayWrite()) {
 644     handler.SignalError(IostatEndfileUnwritable,
 645         "ENDFILE(UNIT=%d) on read-only file", unitNumber());
 646   } else if (IsAfterEndfile()) {
 647     // ENDFILE after ENDFILE
 648   } else {
 649     DoEndfile(handler);
 650     if (IsRecordFile() && access != Access::Direct) {
 651       // Explicit ENDFILE leaves position *after* the endfile record
 652       RUNTIME_CHECK(handler, endfileRecordNumber.has_value());
 653       currentRecordNumber = *endfileRecordNumber + 1;
 654     }
 655   }
 656 }
 657
 658 void ExternalFileUnit::Rewind(IoErrorHandler &handler) {
 659   if (access == Access::Direct) {
 660     handler.SignalError(IostatRewindNonSequential,
 661         "REWIND(UNIT=%d) on non-sequential file", unitNumber());
 662   } else {
 663     SetPosition(0, handler);
 664     currentRecordNumber = 1;
 665     leftTabLimit.reset();
 666   }
 667 }
 668
 669 void ExternalFileUnit::SetPosition(std::int64_t pos, IoErrorHandler &handler) {
 670   DoImpliedEndfile(handler);
 671   frameOffsetInFile_ = pos;
 672   recordOffsetInFrame_ = 0;
 673   if (access == Access::Direct) {
 674     directAccessRecWasSet_ = true;
 675   }
 676   BeginRecord();
 677 }
 678
 679 bool ExternalFileUnit::SetStreamPos(
 680     std::int64_t oneBasedPos, IoErrorHandler &handler) {
 681   if (access != Access::Stream) {
 682     handler.SignalError("POS= may not appear unless ACCESS='STREAM'");
 683     return false;
 684   }
 685   if (oneBasedPos < 1) { // POS=1 is beginning of file (12.6.2.11)
 686     handler.SignalError(
 687         "POS=%zd is invalid", static_cast<std::intmax_t>(oneBasedPos));
 688     return false;
 689   }
 690   SetPosition(oneBasedPos - 1, handler);
 691   // We no longer know which record we're in.  Set currentRecordNumber to
 692   // a large value from whence we can both advance and backspace.
 693   currentRecordNumber = std::numeric_limits<std::int64_t>::max() / 2;
 694   endfileRecordNumber.reset();
 695   return true;
 696 }
 697
 698 bool ExternalFileUnit::SetDirectRec(
 699     std::int64_t oneBasedRec, IoErrorHandler &handler) {
 700   if (access != Access::Direct) {
 701     handler.SignalError("REC= may not appear unless ACCESS='DIRECT'");
 702     return false;
 703   }
 704   if (!openRecl) {
 705     handler.SignalError("RECL= was not specified");
 706     return false;
 707   }
 708   if (oneBasedRec < 1) {
 709     handler.SignalError(
 710         "REC=%zd is invalid", static_cast<std::intmax_t>(oneBasedRec));
 711     return false;
 712   }
 713   currentRecordNumber = oneBasedRec;
 714   SetPosition((oneBasedRec - 1) * *openRecl, handler);
 715   return true;
 716 }
 717
 718 void ExternalFileUnit::EndIoStatement() {
 719   io_.reset();
 720   u_.emplace<std::monostate>();
 721   lock_.Drop();
 722 }
 723
 724 void ExternalFileUnit::BeginSequentialVariableUnformattedInputRecord(
 725     IoErrorHandler &handler) {
 726   std::int32_t header{0}, footer{0};
 727   std::size_t need{recordOffsetInFrame_ + sizeof header};
 728   std::size_t got{ReadFrame(frameOffsetInFile_, need, handler)};
 729   // Try to emit informative errors to help debug corrupted files.
 730   const char *error{nullptr};
 731   if (got < need) {
 732     if (got == recordOffsetInFrame_) {
 733       HitEndOnRead(handler);
 734     } else {
 735       error = "Unformatted variable-length sequential file input failed at "
 736               "record #%jd (file offset %jd): truncated record header";
 737     }
 738   } else {
 739     header = ReadHeaderOrFooter(recordOffsetInFrame_);
 740     recordLength = sizeof header + header; // does not include footer
 741     need = recordOffsetInFrame_ + *recordLength + sizeof footer;
 742     got = ReadFrame(frameOffsetInFile_, need, handler);
 743     if (got < need) {
 744       error = "Unformatted variable-length sequential file input failed at "
 745               "record #%jd (file offset %jd): hit EOF reading record with "
 746               "length %jd bytes";
 747     } else {
 748       footer = ReadHeaderOrFooter(recordOffsetInFrame_ + *recordLength);
 749       if (footer != header) {
 750         error = "Unformatted variable-length sequential file input failed at "
 751                 "record #%jd (file offset %jd): record header has length %jd "
 752                 "that does not match record footer (%jd)";
 753       }
 754     }
 755   }
 756   if (error) {
 757     handler.SignalError(error, static_cast<std::intmax_t>(currentRecordNumber),
 758         static_cast<std::intmax_t>(frameOffsetInFile_),
 759         static_cast<std::intmax_t>(header), static_cast<std::intmax_t>(footer));
 760     // TODO: error recovery
 761   }
 762   positionInRecord = sizeof header;
 763 }
 764
 765 void ExternalFileUnit::BeginVariableFormattedInputRecord(
 766     IoErrorHandler &handler) {
 767   if (this == defaultInput) {
 768     if (defaultOutput) {
 769       defaultOutput->FlushOutput(handler);
 770     }
 771     if (errorOutput) {
 772       errorOutput->FlushOutput(handler);
 773     }
 774   }
 775   std::size_t length{0};
 776   do {
 777     std::size_t need{length + 1};
 778     length =
 779         ReadFrame(frameOffsetInFile_, recordOffsetInFrame_ + need, handler) -
 780         recordOffsetInFrame_;
 781     if (length < need) {
 782       if (length > 0) {
 783         // final record w/o \n
 784         recordLength = length;
 785         unterminatedRecord = true;
 786       } else {
 787         HitEndOnRead(handler);
 788       }
 789       break;
 790     }
 791   } while (!SetVariableFormattedRecordLength());
 792 }
 793
 794 void ExternalFileUnit::BackspaceFixedRecord(IoErrorHandler &handler) {
 795   RUNTIME_CHECK(handler, openRecl.has_value());
 796   if (frameOffsetInFile_ < *openRecl) {
 797     handler.SignalError(IostatBackspaceAtFirstRecord);
 798   } else {
 799     frameOffsetInFile_ -= *openRecl;
 800   }
 801 }
 802
 803 void ExternalFileUnit::BackspaceVariableUnformattedRecord(
 804     IoErrorHandler &handler) {
 805   std::int32_t header{0};
 806   auto headerBytes{static_cast<std::int64_t>(sizeof header)};
 807   frameOffsetInFile_ += recordOffsetInFrame_;
 808   recordOffsetInFrame_ = 0;
 809   if (frameOffsetInFile_ <= headerBytes) {
 810     handler.SignalError(IostatBackspaceAtFirstRecord);
 811     return;
 812   }
 813   // Error conditions here cause crashes, not file format errors, because the
 814   // validity of the file structure before the current record will have been
 815   // checked informatively in NextSequentialVariableUnformattedInputRecord().
 816   std::size_t got{
 817       ReadFrame(frameOffsetInFile_ - headerBytes, headerBytes, handler)};
 818   if (static_cast<std::int64_t>(got) < headerBytes) {
 819     handler.SignalError(IostatShortRead);
 820     return;
 821   }
 822   recordLength = ReadHeaderOrFooter(0);
 823   if (frameOffsetInFile_ < *recordLength + 2 * headerBytes) {
 824     handler.SignalError(IostatBadUnformattedRecord);
 825     return;
 826   }
 827   frameOffsetInFile_ -= *recordLength + 2 * headerBytes;
 828   if (frameOffsetInFile_ >= headerBytes) {
 829     frameOffsetInFile_ -= headerBytes;
 830     recordOffsetInFrame_ = headerBytes;
 831   }
 832   auto need{static_cast<std::size_t>(
 833       recordOffsetInFrame_ + sizeof header + *recordLength)};
 834   got = ReadFrame(frameOffsetInFile_, need, handler);
 835   if (got < need) {
 836     handler.SignalError(IostatShortRead);
 837     return;
 838   }
 839   header = ReadHeaderOrFooter(recordOffsetInFrame_);
 840   if (header != *recordLength) {
 841     handler.SignalError(IostatBadUnformattedRecord);
 842     return;
 843   }
 844 }
 845
 846 // There's no portable memrchr(), unfortunately, and strrchr() would
 847 // fail on a record with a NUL, so we have to do it the hard way.
 848 static const char *FindLastNewline(const char *str, std::size_t length) {
 849   for (const char *p{str + length}; p >= str; p--) {
 850     if (*p == '\n') {
 851       return p;
 852     }
 853   }
 854   return nullptr;
 855 }
 856
 857 void ExternalFileUnit::BackspaceVariableFormattedRecord(
 858     IoErrorHandler &handler) {
 859   // File offset of previous record's newline
 860   auto prevNL{
 861       frameOffsetInFile_ + static_cast<std::int64_t>(recordOffsetInFrame_) - 1};
 862   if (prevNL < 0) {
 863     handler.SignalError(IostatBackspaceAtFirstRecord);
 864     return;
 865   }
 866   while (true) {
 867     if (frameOffsetInFile_ < prevNL) {
 868       if (const char *p{
 869               FindLastNewline(Frame(), prevNL - 1 - frameOffsetInFile_)}) {
 870         recordOffsetInFrame_ = p - Frame() + 1;
 871         recordLength = prevNL - (frameOffsetInFile_ + recordOffsetInFrame_);
 872         break;
 873       }
 874     }
 875     if (frameOffsetInFile_ == 0) {
 876       recordOffsetInFrame_ = 0;
 877       recordLength = prevNL;
 878       break;
 879     }
 880     frameOffsetInFile_ -= std::min<std::int64_t>(frameOffsetInFile_, 1024);
 881     auto need{static_cast<std::size_t>(prevNL + 1 - frameOffsetInFile_)};
 882     auto got{ReadFrame(frameOffsetInFile_, need, handler)};
 883     if (got < need) {
 884       handler.SignalError(IostatShortRead);
 885       return;
 886     }
 887   }
 888   if (Frame()[recordOffsetInFrame_ + *recordLength] != '\n') {
 889     handler.SignalError(IostatMissingTerminator);
 890     return;
 891   }
 892   if (*recordLength > 0 &&
 893       Frame()[recordOffsetInFrame_ + *recordLength - 1] == '\r') {
 894     --*recordLength;
 895   }
 896 }
 897
 898 void ExternalFileUnit::DoImpliedEndfile(IoErrorHandler &handler) {
 899   if (!impliedEndfile_ && direction_ == Direction::Output && IsRecordFile() &&
 900       access != Access::Direct && leftTabLimit) {
 901     // Complete partial record after non-advancing write before
 902     // positioning or closing the unit.  Usually sets impliedEndfile_.
 903     AdvanceRecord(handler);
 904   }
 905   if (impliedEndfile_) {
 906     impliedEndfile_ = false;
 907     if (access != Access::Direct && IsRecordFile() && mayPosition()) {
 908       DoEndfile(handler);
 909     }
 910   }
 911 }
 912
 913 void ExternalFileUnit::DoEndfile(IoErrorHandler &handler) {
 914   if (IsRecordFile() && access != Access::Direct) {
 915     furthestPositionInRecord =
 916         std::max(positionInRecord, furthestPositionInRecord);
 917     if (leftTabLimit) {
 918       // Last read/write was non-advancing, so AdvanceRecord() was not called.
 919       leftTabLimit.reset();
 920       ++currentRecordNumber;
 921     }
 922     endfileRecordNumber = currentRecordNumber;
 923   }
 924   frameOffsetInFile_ += recordOffsetInFrame_ + furthestPositionInRecord;
 925   recordOffsetInFrame_ = 0;
 926   FlushOutput(handler);
 927   Truncate(frameOffsetInFile_, handler);
 928   TruncateFrame(frameOffsetInFile_, handler);
 929   BeginRecord();
 930   impliedEndfile_ = false;
 931 }
 932
 933 void ExternalFileUnit::CommitWrites() {
 934   frameOffsetInFile_ +=
 935       recordOffsetInFrame_ + recordLength.value_or(furthestPositionInRecord);
 936   recordOffsetInFrame_ = 0;
 937   BeginRecord();
 938 }
 939
 940 bool ExternalFileUnit::CheckDirectAccess(IoErrorHandler &handler) {
 941   if (access == Access::Direct) {
 942     RUNTIME_CHECK(handler, openRecl);
 943     if (!directAccessRecWasSet_) {
 944       handler.SignalError(
 945           "No REC= was specified for a data transfer with ACCESS='DIRECT'");
 946       return false;
 947     }
 948   }
 949   return true;
 950 }
 951
 952 void ExternalFileUnit::HitEndOnRead(IoErrorHandler &handler) {
 953   handler.SignalEnd();
 954   if (IsRecordFile() && access != Access::Direct) {
 955     endfileRecordNumber = currentRecordNumber;
 956   }
 957 }
 958
 959 ChildIo &ExternalFileUnit::PushChildIo(IoStatementState &parent) {
 960   OwningPtr<ChildIo> current{std::move(child_)};
 961   Terminator &terminator{parent.GetIoErrorHandler()};
 962   OwningPtr<ChildIo> next{New<ChildIo>{terminator}(parent, std::move(current))};
 963   child_.reset(next.release());
 964   return *child_;
 965 }
 966
 967 void ExternalFileUnit::PopChildIo(ChildIo &child) {
 968   if (child_.get() != &child) {
 969     child.parent().GetIoErrorHandler().Crash(
 970         "ChildIo being popped is not top of stack");
 971   }
 972   child_.reset(child.AcquirePrevious().release()); // deletes top child
 973 }
 974
 975 int ExternalFileUnit::GetAsynchronousId(IoErrorHandler &handler) {
 976   if (!mayAsynchronous()) {
 977     handler.SignalError(IostatBadAsynchronous);
 978     return -1;
 979   } else if (auto least{asyncIdAvailable_.LeastElement()}) {
 980     asyncIdAvailable_.reset(*least);
 981     return static_cast<int>(*least);
 982   } else {
 983     handler.SignalError(IostatTooManyAsyncOps);
 984     return -1;
 985   }
 986 }
 987
 988 bool ExternalFileUnit::Wait(int id) {
 989   if (static_cast<std::size_t>(id) >= asyncIdAvailable_.size() ||
 990       asyncIdAvailable_.test(id)) {
 991     return false;
 992   } else {
 993     if (id == 0) { // means "all IDs"
 994       asyncIdAvailable_.set();
 995       asyncIdAvailable_.reset(0);
 996     } else {
 997       asyncIdAvailable_.set(id);
 998     }
 999     return true;
1000   }
1001 }
1002
1003 std::int32_t ExternalFileUnit::ReadHeaderOrFooter(std::int64_t frameOffset) {
1004   std::int32_t word;
1005   char *wordPtr{reinterpret_cast<char *>(&word)};
1006   std::memcpy(wordPtr, Frame() + frameOffset, sizeof word);
1007   if (swapEndianness_) {
1008     SwapEndianness(wordPtr, sizeof word, sizeof word);
1009   }
1010   return word;
1011 }
1012
1013 void ChildIo::EndIoStatement() {
1014   io_.reset();
1015   u_.emplace<std::monostate>();
1016 }
1017
1018 Iostat ChildIo::CheckFormattingAndDirection(
1019     bool unformatted, Direction direction) {
1020   bool parentIsInput{!parent_.get_if<IoDirectionState<Direction::Output>>()};
1021   bool parentIsFormatted{parentIsInput
1022           ? parent_.get_if<FormattedIoStatementState<Direction::Input>>() !=
1023               nullptr
1024           : parent_.get_if<FormattedIoStatementState<Direction::Output>>() !=
1025               nullptr};
1026   bool parentIsUnformatted{!parentIsFormatted};
1027   if (unformatted != parentIsUnformatted) {
1028     return unformatted ? IostatUnformattedChildOnFormattedParent
1029                        : IostatFormattedChildOnUnformattedParent;
1030   } else if (parentIsInput != (direction == Direction::Input)) {
1031     return parentIsInput ? IostatChildOutputToInputParent
1032                          : IostatChildInputFromOutputParent;
1033   } else {
1034     return IostatOk;
1035   }
1036 }
1037
1038 } // namespace Fortran::runtime::io