1 // Copyright 2012 Google Inc. All Rights Reserved.
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
7 // http://www.apache.org/licenses/LICENSE-2.0
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.
15 #ifndef NINJA_DEPS_LOG_H_
16 #define NINJA_DEPS_LOG_H_
24 #include "timestamp.h"
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.
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
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.
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.
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, output path mtime, input path id, input path id...]
61 /// (The mtime is compared against the on-disk output path mtime
62 /// to verify the stored data is up-to-date.)
63 /// If two records reference the same output the latter one in the file
64 /// wins, allowing updates to just be appended to the file. A separate
65 /// repacking step can run occasionally to remove dead records.
67 DepsLog() : needs_recompaction_(false), file_(NULL) {}
70 // Writing (build-time) interface.
71 bool OpenForWrite(const string& path, string* err);
72 bool RecordDeps(Node* node, TimeStamp mtime, const vector<Node*>& nodes);
73 bool RecordDeps(Node* node, TimeStamp mtime, int node_count, Node** nodes);
76 // Reading (startup-time) interface.
78 Deps(int mtime, int node_count)
79 : mtime(mtime), node_count(node_count), nodes(new Node*[node_count]) {}
80 ~Deps() { delete [] nodes; }
85 bool Load(const string& path, State* state, string* err);
86 Deps* GetDeps(Node* node);
88 /// Rewrite the known log entries, throwing away old data.
89 bool Recompact(const string& path, string* err);
91 /// Returns if the deps entry for a node is still reachable from the manifest.
93 /// The deps log can contain deps entries for files that were built in the
94 /// past but are no longer part of the manifest. This function returns if
95 /// this is the case for a given node. This function is slow, don't call
96 /// it from code that runs on every build.
97 bool IsDepsEntryLiveFor(Node* node);
100 const vector<Node*>& nodes() const { return nodes_; }
101 const vector<Deps*>& deps() const { return deps_; }
104 // Updates the in-memory representation. Takes ownership of |deps|.
105 // Returns true if a prior deps record was deleted.
106 bool UpdateDeps(int out_id, Deps* deps);
107 // Write a node name record, assigning it an id.
108 bool RecordId(Node* node);
110 bool needs_recompaction_;
114 vector<Node*> nodes_;
115 /// Maps id -> deps of that id.
118 friend struct DepsLogTest;
121 #endif // NINJA_DEPS_LOG_H_