flang/runtime/buffer.h

   1 //===-- runtime/buffer.h ----------------------------------------*- C++ -*-===//
   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 // External file buffering
  10
  11 #ifndef FORTRAN_RUNTIME_BUFFER_H_
  12 #define FORTRAN_RUNTIME_BUFFER_H_
  13
  14 #include "io-error.h"
  15 #include "flang/Runtime/memory.h"
  16 #include <algorithm>
  17 #include <cinttypes>
  18 #include <cstring>
  19
  20 namespace Fortran::runtime::io {
  21
  22 void LeftShiftBufferCircularly(char *, std::size_t bytes, std::size_t shift);
  23
  24 // Maintains a view of a contiguous region of a file in a memory buffer.
  25 // The valid data in the buffer may be circular, but any active frame
  26 // will also be contiguous in memory.  The requirement stems from the need to
  27 // preserve read data that may be reused by means of Tn/TLn edit descriptors
  28 // without needing to position the file (which may not always be possible,
  29 // e.g. a socket) and a general desire to reduce system call counts.
  30 //
  31 // Possible scenario with a tiny 32-byte buffer after a ReadFrame or
  32 // WriteFrame with a file offset of 103 to access "DEF":
  33 //
  34 //    fileOffset_ 100 --+  +-+ frame of interest (103:105)
  35 //   file:  ............ABCDEFGHIJKLMNOPQRSTUVWXYZ....
  36 // buffer: [NOPQRSTUVWXYZ......ABCDEFGHIJKLM]   (size_ == 32)
  37 //                             |  +-- frame_ == 3
  38 //                             +----- start_ == 19, length_ == 26
  39 //
  40 // The buffer holds length_ == 26 bytes from file offsets 100:125.
  41 // Those 26 bytes "wrap around" the end of the circular buffer,
  42 // so file offsets 100:112 map to buffer offsets 19:31 ("A..M") and
  43 //    file offsets 113:125 map to buffer offsets  0:12 ("N..Z")
  44 // The 3-byte frame of file offsets 103:105 is contiguous in the buffer
  45 // at buffer offset (start_ + frame_) == 22 ("DEF").
  46
  47 template <typename STORE, std::size_t minBuffer = 65536> class FileFrame {
  48 public:
  49   using FileOffset = std::int64_t;
  50
  51   ~FileFrame() { FreeMemoryAndNullify(buffer_); }
  52
  53   // The valid data in the buffer begins at buffer_[start_] and proceeds
  54   // with possible wrap-around for length_ bytes.  The current frame
  55   // is offset by frame_ bytes into that region and is guaranteed to
  56   // be contiguous for at least as many bytes as were requested.
  57
  58   FileOffset FrameAt() const { return fileOffset_ + frame_; }
  59   char *Frame() const { return buffer_ + start_ + frame_; }
  60   std::size_t FrameLength() const {
  61     return std::min<std::size_t>(length_ - frame_, size_ - (start_ + frame_));
  62   }
  63   std::size_t BytesBufferedBeforeFrame() const { return frame_ - start_; }
  64
  65   // Returns a short frame at a non-fatal EOF.  Can return a long frame as well.
  66   std::size_t ReadFrame(
  67       FileOffset at, std::size_t bytes, IoErrorHandler &handler) {
  68     Flush(handler);
  69     Reallocate(bytes, handler);
  70     std::int64_t newFrame{at - fileOffset_};
  71     if (newFrame < 0 || newFrame > length_) {
  72       Reset(at);
  73     } else {
  74       frame_ = newFrame;
  75     }
  76     RUNTIME_CHECK(handler, at == fileOffset_ + frame_);
  77     if (static_cast<std::int64_t>(start_ + frame_ + bytes) > size_) {
  78       DiscardLeadingBytes(frame_, handler);
  79       MakeDataContiguous(handler, bytes);
  80       RUNTIME_CHECK(handler, at == fileOffset_ + frame_);
  81     }
  82     if (FrameLength() < bytes) {
  83       auto next{start_ + length_};
  84       RUNTIME_CHECK(handler, next < size_);
  85       auto minBytes{bytes - FrameLength()};
  86       auto maxBytes{size_ - next};
  87       auto got{Store().Read(
  88           fileOffset_ + length_, buffer_ + next, minBytes, maxBytes, handler)};
  89       length_ += got;
  90       RUNTIME_CHECK(handler, length_ <= size_);
  91     }
  92     return FrameLength();
  93   }
  94
  95   void WriteFrame(FileOffset at, std::size_t bytes, IoErrorHandler &handler) {
  96     Reallocate(bytes, handler);
  97     std::int64_t newFrame{at - fileOffset_};
  98     if (!dirty_ || newFrame < 0 || newFrame > length_) {
  99       Flush(handler);
 100       Reset(at);
 101     } else if (start_ + newFrame + static_cast<std::int64_t>(bytes) > size_) {
 102       // Flush leading data before "at", retain from "at" onward
 103       Flush(handler, length_ - newFrame);
 104       MakeDataContiguous(handler, bytes);
 105     } else {
 106       frame_ = newFrame;
 107     }
 108     RUNTIME_CHECK(handler, at == fileOffset_ + frame_);
 109     dirty_ = true;
 110     length_ = std::max<std::int64_t>(length_, frame_ + bytes);
 111   }
 112
 113   void Flush(IoErrorHandler &handler, std::int64_t keep = 0) {
 114     if (dirty_) {
 115       while (length_ > keep) {
 116         std::size_t chunk{
 117             std::min<std::size_t>(length_ - keep, size_ - start_)};
 118         std::size_t put{
 119             Store().Write(fileOffset_, buffer_ + start_, chunk, handler)};
 120         DiscardLeadingBytes(put, handler);
 121         if (put < chunk) {
 122           break;
 123         }
 124       }
 125       if (length_ == 0) {
 126         Reset(fileOffset_);
 127       }
 128     }
 129   }
 130
 131   void TruncateFrame(std::int64_t at, IoErrorHandler &handler) {
 132     RUNTIME_CHECK(handler, !dirty_);
 133     if (at <= fileOffset_) {
 134       Reset(at);
 135     } else if (at < fileOffset_ + length_) {
 136       length_ = at - fileOffset_;
 137     }
 138   }
 139
 140 private:
 141   STORE &Store() { return static_cast<STORE &>(*this); }
 142
 143   void Reallocate(std::int64_t bytes, const Terminator &terminator) {
 144     if (bytes > size_) {
 145       char *old{buffer_};
 146       auto oldSize{size_};
 147       size_ = std::max<std::int64_t>(bytes, size_ + minBuffer);
 148       buffer_ =
 149           reinterpret_cast<char *>(AllocateMemoryOrCrash(terminator, size_));
 150       auto chunk{std::min<std::int64_t>(length_, oldSize - start_)};
 151       std::memcpy(buffer_, old + start_, chunk);
 152       start_ = 0;
 153       std::memcpy(buffer_ + chunk, old, length_ - chunk);
 154       FreeMemory(old);
 155     }
 156   }
 157
 158   void Reset(FileOffset at) {
 159     start_ = length_ = frame_ = 0;
 160     fileOffset_ = at;
 161     dirty_ = false;
 162   }
 163
 164   void DiscardLeadingBytes(std::int64_t n, const Terminator &terminator) {
 165     RUNTIME_CHECK(terminator, length_ >= n);
 166     length_ -= n;
 167     if (length_ == 0) {
 168       start_ = 0;
 169     } else {
 170       start_ += n;
 171       if (start_ >= size_) {
 172         start_ -= size_;
 173       }
 174     }
 175     if (frame_ >= n) {
 176       frame_ -= n;
 177     } else {
 178       frame_ = 0;
 179     }
 180     fileOffset_ += n;
 181   }
 182
 183   void MakeDataContiguous(IoErrorHandler &handler, std::size_t bytes) {
 184     if (static_cast<std::int64_t>(start_ + bytes) > size_) {
 185       // Frame would wrap around; shift current data (if any) to force
 186       // contiguity.
 187       RUNTIME_CHECK(handler, length_ < size_);
 188       if (start_ + length_ <= size_) {
 189         // [......abcde..] -> [abcde........]
 190         std::memmove(buffer_, buffer_ + start_, length_);
 191       } else {
 192         // [cde........ab] -> [abcde........]
 193         auto n{start_ + length_ - size_}; // 3 for cde
 194         RUNTIME_CHECK(handler, length_ >= n);
 195         std::memmove(buffer_ + n, buffer_ + start_, length_ - n); // cdeab
 196         LeftShiftBufferCircularly(buffer_, length_, n); // abcde
 197       }
 198       start_ = 0;
 199     }
 200   }
 201
 202   char *buffer_{nullptr};
 203   std::int64_t size_{0}; // current allocated buffer size
 204   FileOffset fileOffset_{0}; // file offset corresponding to buffer valid data
 205   std::int64_t start_{0}; // buffer_[] offset of valid data
 206   std::int64_t length_{0}; // valid data length (can wrap)
 207   std::int64_t frame_{0}; // offset of current frame in valid data
 208   bool dirty_{false};
 209 };
 210 } // namespace Fortran::runtime::io
 211 #endif // FORTRAN_RUNTIME_BUFFER_H_