1 // Copyright 2012 Google Inc. All Rights Reserved.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 //     http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
15 #ifndef NINJA_DEPS_LOG_H_
16 #define NINJA_DEPS_LOG_H_
17 
18 #include <string>
19 #include <vector>
20 
21 #include <stdio.h>
22 
23 #include "load_status.h"
24 #include "timestamp.h"
25 
26 struct Node;
27 struct State;
28 
29 /// As build commands run they can output extra dependency information
30 /// (e.g. header dependencies for C source) dynamically.  DepsLog collects
31 /// that information at build time and uses it for subsequent builds.
32 ///
33 /// The on-disk format is based on two primary design constraints:
34 /// - it must be written to as a stream (during the build, which may be
35 ///   interrupted);
36 /// - it can be read all at once on startup.  (Alternative designs, where
37 ///   it contains indexing information, were considered and discarded as
38 ///   too complicated to implement; if the file is small than reading it
39 ///   fully on startup is acceptable.)
40 /// Here are some stats from the Windows Chrome dependency files, to
41 /// help guide the design space.  The total text in the files sums to
42 /// 90mb so some compression is warranted to keep load-time fast.
43 /// There's about 10k files worth of dependencies that reference about
44 /// 40k total paths totalling 2mb of unique strings.
45 ///
46 /// Based on these stats, here's the current design.
47 /// The file is structured as version header followed by a sequence of records.
48 /// Each record is either a path string or a dependency list.
49 /// Numbering the path strings in file order gives them dense integer ids.
50 /// A dependency list maps an output id to a list of input ids.
51 ///
52 /// Concretely, a record is:
53 ///    four bytes record length, high bit indicates record type
54 ///      (but max record sizes are capped at 512kB)
55 ///    path records contain the string name of the path, followed by up to 3
56 ///      padding bytes to align on 4 byte boundaries, followed by the
57 ///      one's complement of the expected index of the record (to detect
58 ///      concurrent writes of multiple ninja processes to the log).
59 ///    dependency records are an array of 4-byte integers
60 ///      [output path id,
61 ///       output path mtime (lower 4 bytes), output path mtime (upper 4 bytes),
62 ///       input path id, input path id...]
63 ///      (The mtime is compared against the on-disk output path mtime
64 ///      to verify the stored data is up-to-date.)
65 /// If two records reference the same output the latter one in the file
66 /// wins, allowing updates to just be appended to the file.  A separate
67 /// repacking step can run occasionally to remove dead records.
68 struct DepsLog {
DepsLogDepsLog69   DepsLog() : needs_recompaction_(false), file_(NULL) {}
70   ~DepsLog();
71 
72   // Writing (build-time) interface.
73   bool OpenForWrite(const std::string& path, std::string* err);
74   bool RecordDeps(Node* node, TimeStamp mtime, const std::vector<Node*>& nodes);
75   bool RecordDeps(Node* node, TimeStamp mtime, int node_count, Node** nodes);
76   void Close();
77 
78   // Reading (startup-time) interface.
79   struct Deps {
DepsDepsLog::Deps80     Deps(int64_t mtime, int node_count)
81         : mtime(mtime), node_count(node_count), nodes(new Node*[node_count]) {}
~DepsDepsLog::Deps82     ~Deps() { delete [] nodes; }
83     TimeStamp mtime;
84     int node_count;
85     Node** nodes;
86   };
87   LoadStatus Load(const std::string& path, State* state, std::string* err);
88   Deps* GetDeps(Node* node);
89 
90   /// Rewrite the known log entries, throwing away old data.
91   bool Recompact(const std::string& path, std::string* err);
92 
93   /// Returns if the deps entry for a node is still reachable from the manifest.
94   ///
95   /// The deps log can contain deps entries for files that were built in the
96   /// past but are no longer part of the manifest.  This function returns if
97   /// this is the case for a given node.  This function is slow, don't call
98   /// it from code that runs on every build.
99   bool IsDepsEntryLiveFor(Node* node);
100 
101   /// Used for tests.
nodesDepsLog102   const std::vector<Node*>& nodes() const { return nodes_; }
depsDepsLog103   const std::vector<Deps*>& deps() const { return deps_; }
104 
105  private:
106   // Updates the in-memory representation.  Takes ownership of |deps|.
107   // Returns true if a prior deps record was deleted.
108   bool UpdateDeps(int out_id, Deps* deps);
109   // Write a node name record, assigning it an id.
110   bool RecordId(Node* node);
111 
112   /// Should be called before using file_. When false is returned, errno will
113   /// be set.
114   bool OpenForWriteIfNeeded();
115 
116   bool needs_recompaction_;
117   FILE* file_;
118   std::string file_path_;
119 
120   /// Maps id -> Node.
121   std::vector<Node*> nodes_;
122   /// Maps id -> deps of that id.
123   std::vector<Deps*> deps_;
124 
125   friend struct DepsLogTest;
126 };
127 
128 #endif  // NINJA_DEPS_LOG_H_
129