DataStream.cpp revision 302408 
1//===--- llvm/Support/DataStream.cpp - Lazy streamed data -----------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements DataStreamer, which fetches bytes of Data from
11// a stream source. It provides support for streaming (lazy reading) of
12// bitcode. An example implementation of streaming from a file or stdin
13// is included.
14//
15//===----------------------------------------------------------------------===//
16
17#include "llvm/Support/DataStream.h"
18#include "llvm/ADT/Statistic.h"
19#include "llvm/ADT/STLExtras.h"
20#include "llvm/Support/FileSystem.h"
21#include "llvm/Support/Program.h"
22#include <string>
23#include <system_error>
24#if !defined(_MSC_VER) && !defined(__MINGW32__)
25#include <unistd.h>
26#else
27#include <io.h>
28#endif
29using namespace llvm;
30
31#define DEBUG_TYPE "Data-stream"
32
33// Interface goals:
34// * StreamingMemoryObject doesn't care about complexities like using
35//   threads/async callbacks to actually overlap download+compile
36// * Don't want to duplicate Data in memory
37// * Don't need to know total Data len in advance
38// Non-goals:
39// StreamingMemoryObject already has random access so this interface only does
40// in-order streaming (no arbitrary seeking, else we'd have to buffer all the
41// Data here in addition to MemoryObject).  This also means that if we want
42// to be able to to free Data, BitstreamBytes/BitcodeReader will implement it
43
44STATISTIC(NumStreamFetches, "Number of calls to Data stream fetch");
45
46namespace llvm {
47DataStreamer::~DataStreamer() {}
48}
49
50namespace {
51
52// Very simple stream backed by a file. Mostly useful for stdin and debugging;
53// actual file access is probably still best done with mmap.
54class DataFileStreamer : public DataStreamer {
55 int Fd;
56public:
57  DataFileStreamer() : Fd(0) {}
58  ~DataFileStreamer() override { close(Fd); }
59  size_t GetBytes(unsigned char *buf, size_t len) override {
60    NumStreamFetches++;
61    return read(Fd, buf, len);
62  }
63
64  std::error_code OpenFile(const std::string &Filename) {
65    if (Filename == "-") {
66      Fd = 0;
67      sys::ChangeStdinToBinary();
68      return std::error_code();
69    }
70
71    return sys::fs::openFileForRead(Filename, Fd);
72  }
73};
74
75}
76
77std::unique_ptr<DataStreamer>
78llvm::getDataFileStreamer(const std::string &Filename, std::string *StrError) {
79  std::unique_ptr<DataFileStreamer> s = make_unique<DataFileStreamer>();
80  if (std::error_code e = s->OpenFile(Filename)) {
81    *StrError = std::string("Could not open ") + Filename + ": " +
82        e.message() + "\n";
83    return nullptr;
84  }
85  return std::move(s);
86}
87