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// Copyright 2012 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef NINJA_DEPS_LOG_H_
#define NINJA_DEPS_LOG_H_
#include <string>
#include <vector>
using namespace std;
#include <stdio.h>
#include "timestamp.h"
struct Node;
struct State;
/// As build commands run they can output extra dependency information
/// (e.g. header dependencies for C source) dynamically. DepsLog collects
/// that information at build time and uses it for subsequent builds.
///
/// The on-disk format is based on two primary design constraints:
/// - it must be written to as a stream (during the build, which may be
/// interrupted);
/// - it can be read all at once on startup. (Alternative designs, where
/// it contains indexing information, were considered and discarded as
/// too complicated to implement; if the file is small than reading it
/// fully on startup is acceptable.)
/// Here are some stats from the Windows Chrome dependency files, to
/// help guide the design space. The total text in the files sums to
/// 90mb so some compression is warranted to keep load-time fast.
/// There's about 10k files worth of dependencies that reference about
/// 40k total paths totalling 2mb of unique strings.
///
/// Based on these stats, here's the current design.
/// The file is structured as version header followed by a sequence of records.
/// Each record is either a path string or a dependency list.
/// Numbering the path strings in file order gives them dense integer ids.
/// A dependency list maps an output id to a list of input ids.
///
/// Concretely, a record is:
/// four bytes record length, high bit indicates record type
/// (but max record sizes are capped at 512kB)
/// path records contain the string name of the path, followed by up to 3
/// padding bytes to align on 4 byte boundaries, followed by the
/// one's complement of the expected index of the record (to detect
/// concurrent writes of multiple ninja processes to the log).
/// dependency records are an array of 4-byte integers
/// [output path id,
/// output path mtime (lower 4 bytes), output path mtime (upper 4 bytes),
/// input path id, input path id...]
/// (The mtime is compared against the on-disk output path mtime
/// to verify the stored data is up-to-date.)
/// If two records reference the same output the latter one in the file
/// wins, allowing updates to just be appended to the file. A separate
/// repacking step can run occasionally to remove dead records.
struct DepsLog {
DepsLog() : needs_recompaction_(false), file_(NULL) {}
~DepsLog();
// Writing (build-time) interface.
bool OpenForWrite(const string& path, string* err);
bool RecordDeps(Node* node, TimeStamp mtime, const vector<Node*>& nodes);
bool RecordDeps(Node* node, TimeStamp mtime, int node_count, Node** nodes);
void Close();
// Reading (startup-time) interface.
struct Deps {
Deps(int64_t mtime, int node_count)
: mtime(mtime), node_count(node_count), nodes(new Node*[node_count]) {}
~Deps() { delete [] nodes; }
TimeStamp mtime;
int node_count;
Node** nodes;
};
bool Load(const string& path, State* state, string* err);
Deps* GetDeps(Node* node);
/// Rewrite the known log entries, throwing away old data.
bool Recompact(const string& path, string* err);
/// Returns if the deps entry for a node is still reachable from the manifest.
///
/// The deps log can contain deps entries for files that were built in the
/// past but are no longer part of the manifest. This function returns if
/// this is the case for a given node. This function is slow, don't call
/// it from code that runs on every build.
bool IsDepsEntryLiveFor(Node* node);
/// Used for tests.
const vector<Node*>& nodes() const { return nodes_; }
const vector<Deps*>& deps() const { return deps_; }
private:
// Updates the in-memory representation. Takes ownership of |deps|.
// Returns true if a prior deps record was deleted.
bool UpdateDeps(int out_id, Deps* deps);
// Write a node name record, assigning it an id.
bool RecordId(Node* node);
bool needs_recompaction_;
FILE* file_;
/// Maps id -> Node.
vector<Node*> nodes_;
/// Maps id -> deps of that id.
vector<Deps*> deps_;
friend struct DepsLogTest;
};
#endif // NINJA_DEPS_LOG_H_