aboutsummaryrefslogtreecommitdiff
path: root/libbuild2/depdb.hxx
blob: ecc1f3885f403e1ee506241924efe9de4e346235 (plain)
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
// file      : libbuild2/depdb.hxx -*- C++ -*-
// license   : MIT; see accompanying LICENSE file

#ifndef LIBBUILD2_DEPDB_HXX
#define LIBBUILD2_DEPDB_HXX

#include <cstring> // strlen()

#include <libbuild2/types.hxx>
#include <libbuild2/utility.hxx>

#include <libbuild2/export.hxx>

namespace build2
{
  // Auxiliary dependency database (those .d files). Prints the diagnostics
  // and fails on system and IO errors.
  //
  // This is a strange beast: a line-oriented, streaming database that can, at
  // some point, be switched from reading to (over)writing. The idea is to
  // store auxiliary/ad-hoc dependency information in the "invalidation"
  // order. That is, if an earlier line is out of date, then all the
  // subsequent ones are out of date as well.
  //
  // As an example, consider a dependency database for foo.o which is built
  // from foo.cxx by the cxx.compile rule. The first line could be the rule
  // name itself (perhaps with the version). If a different rule is now
  // building foo.o, then any dep info that was saved by cxx.compile is
  // probably useless. Next we can have the command line options that were
  // used to build foo.o. Then could come the source file name followed by the
  // extracted header dependencies. If the compile options or the source file
  // name have changed, then the header dependencies are likely to have
  // changed as well.
  //
  // As an example, here is what our foo.o.d could look like (the first line
  // is the database format version and the last '\0' character is the end
  // marker):
  //
  // 1
  // cxx.compile 1
  // g++-4.8 -I/tmp/foo -O3
  // /tmp/foo/foo.cxx
  // /tmp/foo/foo.hxx
  // /usr/include/string.h
  // /usr/include/stdlib.h
  // /tmp/foo/bar.hxx
  // ^@
  //
  // A race is possible between updating the database and the target. For
  // example, we may detect a line mismatch that renders the target out-of-
  // date (say, compile options in the above example). We update the database
  // but before getting a chance to update the target, we get interrupted. On
  // a subsequent re-run, because the database has been updated, we will miss
  // the "target requires update" condition.
  //
  // If we assume that an update of the database also means an update of the
  // target, then this "interrupted update" situation can be easily detected
  // by comparing the database and target modification timestamps. This is
  // also used to handle the dry-run mode where we essentially do the
  // interruption ourselves.
  //
  struct LIBBUILD2_SYMEXPORT depdb_base
  {
    explicit
    depdb_base (const path&, timestamp);

    ~depdb_base ();

    enum class state {read, read_eof, write} state_;

    union
    {
      ifdstream is_; // read, read_eof
      ofdstream os_; // write
    };

    butl::fdbuf* buf_; // Current buffer (for tellg()/tellp()).
  };

  class LIBBUILD2_SYMEXPORT depdb: private depdb_base
  {
  public:
    using path_type = build2::path;

    // The modification time of the database only makes sense while reading
    // (in the write mode it will be set to timestamp_unknown).
    //
    // If touch is set to true, update the database modification time in
    // close() even if otherwise no modifications are necessary (i.e., the
    // database is in the read mode and is at eof).
    //
    path_type path;
    timestamp mtime;
    bool      touch;

    // Open the database for reading. Note that if the file does not exist,
    // has wrong format version, or is corrupt, then the database will be
    // immediately switched to writing.
    //
    // The failure commonly happens when the user tries to stash the target in
    // a non-existent subdirectory but forgets to add the corresponding fsdir{}
    // prerequisite. That's why the issued diagnostics may provide the
    // corresponding hint.
    //
    explicit
    depdb (path_type);

    // Close the database. If this function is not called, then the database
    // may be left in the old/currupt state. Note that in the read mode this
    // function will "chop off" lines that haven't been read.
    //
    // Make sure to also call check_mtime() after updating the target to
    // perform the target/database modification times sanity checks.
    //
    void
    close ();

    // Flush any unwritten data to disk. This is primarily useful when reusing
    // a (partially written) database as an input to external programs (e.g.,
    // as a module map).
    //
    void
    flush ();

    // Perform target/database modification times sanity check.
    //
    // Note that it would also be good to compare the target timestamp against
    // the newest prerequisite. However, obtaining this information would cost
    // extra (see execute_prerequisites()). So maybe later, if we get a case
    // where this is a problem (in a sense, the database is a buffer between
    // prerequisites and the target).
    //
    void
    check_mtime (const path_type& target, timestamp end = timestamp_unknown);

    static void
    check_mtime (timestamp start,
                 const path_type& db,
                 const path_type& target,
                 timestamp end);

    // Return true if mtime checks are enabled.
    //
    static bool
    mtime_check ();

    // Read the next line. If the result is not NULL, then it is a pointer to
    // the next line in the database (which you are free to move from). If you
    // then call write(), this line will be overwritten.
    //
    // If the result is NULL, then it means no next line is unavailable. This
    // can be due to several reasons:
    //
    // - eof reached (you can detect this by calling more() before read())
    // - database is already in the write mode
    // - the next line (and the rest of the database are corrupt)
    //
    string*
    read () {return state_ == state::write ? nullptr : read_ ();}

    // Return true if the database is in the read mode and there is at least
    // one more line available. Note that there is no guarantee that the line
    // is not corrupt. In other words, read() can still return NULL, it just
    // won't be because of eof.
    //
    bool
    more () const {return state_ == state::read;}

    bool
    reading () const {return state_ != state::write;}

    bool
    writing () const {return state_ == state::write;}

    // Skip to the end of the database and return true if it is valid.
    // Otherwise, return false, in which case the database must be
    // overwritten. Note that this function expects the database to be in the
    // read state.
    //
    bool
    skip ();

    // Write the next line. If nl is false then don't write the newline yet.
    // Note that this switches the database into the write mode and no further
    // reading will be possible.
    //
    void
    write (const string& l, bool nl = true) {write (l.c_str (), l.size (), nl);}

    void
    write (const path_type& p, bool nl = true) {write (p.string (), nl);}

    void
    write (const char* s, bool nl = true) {write (s, std::strlen (s), nl);}

    void
    write (const char*, size_t, bool nl = true);

    void
    write (char, bool nl = true);

    // Mark the previously read line as to be overwritte.
    //
    void
    write () {if (state_ != state::write) change ();}

    // Read the next line and compare it to the expected value. If it matches,
    // return NULL. Otherwise, overwrite it and return the old value (which
    // could also be NULL). This strange-sounding result semantics is used to
    // detect the "there is a value but it does not match" case for tracing:
    //
    // if (string* o = d.expect (...))
    //   l4 ([&]{trace << "X mismatch forcing update of " << t;});
    //
    string*
    expect (const string& v)
    {
      string* l (read ());
      if (l == nullptr || *l != v)
      {
        write (v);
        return l;
      }

      return nullptr;
    }

    string*
    expect (const path_type& v)
    {
      string* l (read ());
      if (l == nullptr ||
          path_type::traits_type::compare (*l, v.string ()) != 0)
      {
        write (v);
        return l;
      }

      return nullptr;
    }

    string*
    expect (const char* v)
    {
      string* l (read ());
      if (l == nullptr || *l != v)
      {
        write (v);
        return l;
      }

      return nullptr;
    }

    // Could be supported if required.
    //
    depdb (depdb&&) = delete;
    depdb (const depdb&) = delete;

    depdb& operator= (depdb&&) = delete;
    depdb& operator= (const depdb&) = delete;

  private:
    depdb (path_type&&, timestamp);

    void
    change (bool truncate = true);

    string*
    read_ ();

    void
    check_mtime_ (const path_type&, timestamp);

    static void
    check_mtime_ (timestamp, const path_type&, const path_type&, timestamp);

  private:
    uint64_t  pos_;   // Start of the last returned line.
    string    line_;  // Current line.
    timestamp start_; // Sequence start (mtime check).
  };
}

#include <libbuild2/depdb.ixx>

#endif // LIBBUILD2_DEPDB_HXX