circular_raw_ostream.h revision 288943 
1//===-- llvm/Support/circular_raw_ostream.h - Buffered streams --*- C++ -*-===//
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 contains raw_ostream implementations for streams to do circular
11// buffering of their output.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_SUPPORT_CIRCULAR_RAW_OSTREAM_H
16#define LLVM_SUPPORT_CIRCULAR_RAW_OSTREAM_H
17
18#include "llvm/Support/raw_ostream.h"
19
20namespace llvm
21{
22  /// circular_raw_ostream - A raw_ostream which *can* save its data
23  /// to a circular buffer, or can pass it through directly to an
24  /// underlying stream if specified with a buffer of zero.
25  ///
26  class circular_raw_ostream : public raw_ostream {
27  public:
28    /// TAKE_OWNERSHIP - Tell this stream that it owns the underlying
29    /// stream and is responsible for cleanup, memory management
30    /// issues, etc.
31    ///
32    static const bool TAKE_OWNERSHIP = true;
33
34    /// REFERENCE_ONLY - Tell this stream it should not manage the
35    /// held stream.
36    ///
37    static const bool REFERENCE_ONLY = false;
38
39  private:
40    /// TheStream - The real stream we output to. We set it to be
41    /// unbuffered, since we're already doing our own buffering.
42    ///
43    raw_ostream *TheStream;
44
45    /// OwnsStream - Are we responsible for managing the underlying
46    /// stream?
47    ///
48    bool OwnsStream;
49
50    /// BufferSize - The size of the buffer in bytes.
51    ///
52    size_t BufferSize;
53
54    /// BufferArray - The actual buffer storage.
55    ///
56    char *BufferArray;
57
58    /// Cur - Pointer to the current output point in BufferArray.
59    ///
60    char *Cur;
61
62    /// Filled - Indicate whether the buffer has been completely
63    /// filled.  This helps avoid garbage output.
64    ///
65    bool Filled;
66
67    /// Banner - A pointer to a banner to print before dumping the
68    /// log.
69    ///
70    const char *Banner;
71
72    /// flushBuffer - Dump the contents of the buffer to Stream.
73    ///
74    void flushBuffer() {
75      if (Filled)
76        // Write the older portion of the buffer.
77        TheStream->write(Cur, BufferArray + BufferSize - Cur);
78      // Write the newer portion of the buffer.
79      TheStream->write(BufferArray, Cur - BufferArray);
80      Cur = BufferArray;
81      Filled = false;
82    }
83
84    void write_impl(const char *Ptr, size_t Size) override;
85
86    /// current_pos - Return the current position within the stream,
87    /// not counting the bytes currently in the buffer.
88    ///
89    uint64_t current_pos() const override {
90      // This has the same effect as calling TheStream.current_pos(),
91      // but that interface is private.
92      return TheStream->tell() - TheStream->GetNumBytesInBuffer();
93    }
94
95  public:
96    /// circular_raw_ostream - Construct an optionally
97    /// circular-buffered stream, handing it an underlying stream to
98    /// do the "real" output.
99    ///
100    /// As a side effect, if BuffSize is nonzero, the given Stream is
101    /// set to be Unbuffered.  This is because circular_raw_ostream
102    /// does its own buffering, so it doesn't want another layer of
103    /// buffering to be happening underneath it.
104    ///
105    /// "Owns" tells the circular_raw_ostream whether it is
106    /// responsible for managing the held stream, doing memory
107    /// management of it, etc.
108    ///
109    circular_raw_ostream(raw_ostream &Stream, const char *Header,
110                         size_t BuffSize = 0, bool Owns = REFERENCE_ONLY)
111        : raw_ostream(/*unbuffered*/ true), TheStream(nullptr),
112          OwnsStream(Owns), BufferSize(BuffSize), BufferArray(nullptr),
113          Filled(false), Banner(Header) {
114      if (BufferSize != 0)
115        BufferArray = new char[BufferSize];
116      Cur = BufferArray;
117      setStream(Stream, Owns);
118    }
119
120    ~circular_raw_ostream() override {
121      flush();
122      flushBufferWithBanner();
123      releaseStream();
124      delete[] BufferArray;
125    }
126
127    /// setStream - Tell the circular_raw_ostream to output a
128    /// different stream.  "Owns" tells circular_raw_ostream whether
129    /// it should take responsibility for managing the underlying
130    /// stream.
131    ///
132    void setStream(raw_ostream &Stream, bool Owns = REFERENCE_ONLY) {
133      releaseStream();
134      TheStream = &Stream;
135      OwnsStream = Owns;
136    }
137
138    /// flushBufferWithBanner - Force output of the buffer along with
139    /// a small header.
140    ///
141    void flushBufferWithBanner();
142
143  private:
144    /// releaseStream - Delete the held stream if needed. Otherwise,
145    /// transfer the buffer settings from this circular_raw_ostream
146    /// back to the underlying stream.
147    ///
148    void releaseStream() {
149      if (!TheStream)
150        return;
151      if (OwnsStream)
152        delete TheStream;
153    }
154  };
155} // end llvm namespace
156
157
158#endif
159