src/build.cc

// Copyright 2011 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.

#include "build.h"

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <climits>
#include <stdint.h>
#include <functional>

#if defined(__SVR4) && defined(__sun)
#include <sys/termios.h>
#endif

#include "build_log.h"
#include "clparser.h"
#include "debug_flags.h"
#include "depfile_parser.h"
#include "deps_log.h"
#include "disk_interface.h"
#include "graph.h"
#include "metrics.h"
#include "state.h"
#include "status.h"
#include "subprocess.h"
#include "util.h"

using namespace std;

namespace {

/// A CommandRunner that doesn't actually run the commands.
struct DryRunCommandRunner : public CommandRunner {
  virtual ~DryRunCommandRunner() {}

  // Overridden from CommandRunner:
  virtual size_t CanRunMore() const;
  virtual bool StartCommand(Edge* edge);
  virtual bool WaitForCommand(Result* result);

 private:
  queue<Edge*> finished_;
};

size_t DryRunCommandRunner::CanRunMore() const {
  return SIZE_MAX;
}

bool DryRunCommandRunner::StartCommand(Edge* edge) {
  finished_.push(edge);
  return true;
}

bool DryRunCommandRunner::WaitForCommand(Result* result) {
   if (finished_.empty())
     return false;

   result->status = ExitSuccess;
   result->edge = finished_.front();
   finished_.pop();
   return true;
}

}  // namespace

Plan::Plan(Builder* builder)
  : builder_(builder)
  , command_edges_(0)
  , wanted_edges_(0)
{}

void Plan::Reset() {
  command_edges_ = 0;
  wanted_edges_ = 0;
  ready_.clear();
  want_.clear();
}

bool Plan::AddTarget(const Node* target, string* err) {
  targets_.push_back(target);
  return AddSubTarget(target, NULL, err, NULL);
}

bool Plan::AddSubTarget(const Node* node, const Node* dependent, string* err,
                        set<Edge*>* dyndep_walk) {
  Edge* edge = node->in_edge();
  if (!edge) {
     // Leaf node, this can be either a regular input from the manifest
     // (e.g. a source file), or an implicit input from a depfile or dyndep
     // file. In the first case, a dirty flag means the file is missing,
     // and the build should stop. In the second, do not do anything here
     // since there is no producing edge to add to the plan.
     if (node->dirty() && !node->generated_by_dep_loader()) {
       string referenced;
       if (dependent)
         referenced = ", needed by '" + dependent->path() + "',";
       *err = "'" + node->path() + "'" + referenced +
              " missing and no known rule to make it";
     }
     return false;
  }

  if (edge->outputs_ready())
    return false;  // Don't need to do anything.

  // If an entry in want_ does not already exist for edge, create an entry which
  // maps to kWantNothing, indicating that we do not want to build this entry itself.
  pair<map<Edge*, Want>::iterator, bool> want_ins =
    want_.insert(make_pair(edge, kWantNothing));
  Want& want = want_ins.first->second;

  if (dyndep_walk && want == kWantToFinish)
    return false;  // Don't need to do anything with already-scheduled edge.

  // If we do need to build edge and we haven't already marked it as wanted,
  // mark it now.
  if (node->dirty() && want == kWantNothing) {
    want = kWantToStart;
    EdgeWanted(edge);
  }

  if (dyndep_walk)
    dyndep_walk->insert(edge);

  if (!want_ins.second)
    return true;  // We've already processed the inputs.

  for (vector<Node*>::iterator i = edge->inputs_.begin();
       i != edge->inputs_.end(); ++i) {
    if (!AddSubTarget(*i, node, err, dyndep_walk) && !err->empty())
      return false;
  }

  return true;
}

void Plan::EdgeWanted(const Edge* edge) {
  ++wanted_edges_;
  if (!edge->is_phony()) {
    ++command_edges_;
    if (builder_)
      builder_->status_->EdgeAddedToPlan(edge);
  }
}

Edge* Plan::FindWork() {
  if (ready_.empty())
    return NULL;

  Edge* work = ready_.top();
  ready_.pop();
  return work;
}

void Plan::ScheduleWork(map<Edge*, Want>::iterator want_e) {
  if (want_e->second == kWantToFinish) {
    // This edge has already been scheduled.  We can get here again if an edge
    // and one of its dependencies share an order-only input, or if a node
    // duplicates an out edge (see https://github.com/ninja-build/ninja/pull/519).
    // Avoid scheduling the work again.
    return;
  }
  assert(want_e->second == kWantToStart);
  want_e->second = kWantToFinish;

  Edge* edge = want_e->first;
  Pool* pool = edge->pool();
  if (pool->ShouldDelayEdge()) {
    pool->DelayEdge(edge);
    pool->RetrieveReadyEdges(&ready_);
  } else {
    pool->EdgeScheduled(*edge);
    ready_.push(edge);
  }
}

bool Plan::EdgeFinished(Edge* edge, EdgeResult result, string* err) {
  map<Edge*, Want>::iterator e = want_.find(edge);
  assert(e != want_.end());
  bool directly_wanted = e->second != kWantNothing;

  // See if this job frees up any delayed jobs.
  if (directly_wanted)
    edge->pool()->EdgeFinished(*edge);
  edge->pool()->RetrieveReadyEdges(&ready_);

  // The rest of this function only applies to successful commands.
  if (result != kEdgeSucceeded)
    return true;

  if (directly_wanted)
    --wanted_edges_;
  want_.erase(e);
  edge->outputs_ready_ = true;

  // Check off any nodes we were waiting for with this edge.
  for (vector<Node*>::iterator o = edge->outputs_.begin();
       o != edge->outputs_.end(); ++o) {
    if (!NodeFinished(*o, err))
      return false;
  }
  return true;
}

bool Plan::NodeFinished(Node* node, string* err) {
  // If this node provides dyndep info, load it now.
  if (node->dyndep_pending()) {
    assert(builder_ && "dyndep requires Plan to have a Builder");
    // Load the now-clean dyndep file.  This will also update the
    // build plan and schedule any new work that is ready.
    return builder_->LoadDyndeps(node, err);
  }

  // See if we we want any edges from this node.
  for (vector<Edge*>::const_iterator oe = node->out_edges().begin();
       oe != node->out_edges().end(); ++oe) {
    map<Edge*, Want>::iterator want_e = want_.find(*oe);
    if (want_e == want_.end())
      continue;

    // See if the edge is now ready.
    if (!EdgeMaybeReady(want_e, err))
      return false;
  }
  return true;
}

bool Plan::EdgeMaybeReady(map<Edge*, Want>::iterator want_e, string* err) {
  Edge* edge = want_e->first;
  if (edge->AllInputsReady()) {
    if (want_e->second != kWantNothing) {
      ScheduleWork(want_e);
    } else {
      // We do not need to build this edge, but we might need to build one of
      // its dependents.
      if (!EdgeFinished(edge, kEdgeSucceeded, err))
        return false;
    }
  }
  return true;
}

bool Plan::CleanNode(DependencyScan* scan, Node* node, string* err) {
  node->set_dirty(false);

  for (vector<Edge*>::const_iterator oe = node->out_edges().begin();
       oe != node->out_edges().end(); ++oe) {
    // Don't process edges that we don't actually want.
    map<Edge*, Want>::iterator want_e = want_.find(*oe);
    if (want_e == want_.end() || want_e->second == kWantNothing)
      continue;

    // Don't attempt to clean an edge if it failed to load deps.
    if ((*oe)->deps_missing_)
      continue;

    // If all non-order-only inputs for this edge are now clean,
    // we might have changed the dirty state of the outputs.
    vector<Node*>::iterator
        begin = (*oe)->inputs_.begin(),
        end = (*oe)->inputs_.end() - (*oe)->order_only_deps_;
#if __cplusplus < 201703L
#define MEM_FN mem_fun
#else
#define MEM_FN mem_fn  // mem_fun was removed in C++17.
#endif
    if (find_if(begin, end, MEM_FN(&Node::dirty)) == end) {
      // Recompute most_recent_input.
      Node* most_recent_input = NULL;
      for (vector<Node*>::iterator i = begin; i != end; ++i) {
        if (!most_recent_input || (*i)->mtime() > most_recent_input->mtime())
          most_recent_input = *i;
      }

      // Now, this edge is dirty if any of the outputs are dirty.
      // If the edge isn't dirty, clean the outputs and mark the edge as not
      // wanted.
      bool outputs_dirty = false;
      if (!scan->RecomputeOutputsDirty(*oe, most_recent_input,
                                       &outputs_dirty, err)) {
        return false;
      }
      if (!outputs_dirty) {
        for (vector<Node*>::iterator o = (*oe)->outputs_.begin();
             o != (*oe)->outputs_.end(); ++o) {
          if (!CleanNode(scan, *o, err))
            return false;
        }

        want_e->second = kWantNothing;
        --wanted_edges_;
        if (!(*oe)->is_phony()) {
          --command_edges_;
          if (builder_)
            builder_->status_->EdgeRemovedFromPlan(*oe);
        }
      }
    }
  }
  return true;
}

bool Plan::DyndepsLoaded(DependencyScan* scan, const Node* node,
                         const DyndepFile& ddf, string* err) {
  // Recompute the dirty state of all our direct and indirect dependents now
  // that our dyndep information has been loaded.
  if (!RefreshDyndepDependents(scan, node, err))
    return false;

  // We loaded dyndep information for those out_edges of the dyndep node that
  // specify the node in a dyndep binding, but they may not be in the plan.
  // Starting with those already in the plan, walk newly-reachable portion
  // of the graph through the dyndep-discovered dependencies.

  // Find edges in the the build plan for which we have new dyndep info.
  std::vector<DyndepFile::const_iterator> dyndep_roots;
  for (DyndepFile::const_iterator oe = ddf.begin(); oe != ddf.end(); ++oe) {
    Edge* edge = oe->first;

    // If the edge outputs are ready we do not need to consider it here.
    if (edge->outputs_ready())
      continue;

    map<Edge*, Want>::iterator want_e = want_.find(edge);

    // If the edge has not been encountered before then nothing already in the
    // plan depends on it so we do not need to consider the edge yet either.
    if (want_e == want_.end())
      continue;

    // This edge is already in the plan so queue it for the walk.
    dyndep_roots.push_back(oe);
  }

  // Walk dyndep-discovered portion of the graph to add it to the build plan.
  std::set<Edge*> dyndep_walk;
  for (std::vector<DyndepFile::const_iterator>::iterator
       oei = dyndep_roots.begin(); oei != dyndep_roots.end(); ++oei) {
    DyndepFile::const_iterator oe = *oei;
    for (vector<Node*>::const_iterator i = oe->second.implicit_inputs_.begin();
         i != oe->second.implicit_inputs_.end(); ++i) {
      if (!AddSubTarget(*i, oe->first->outputs_[0], err, &dyndep_walk) &&
          !err->empty())
        return false;
    }
  }

  // Add out edges from this node that are in the plan (just as
  // Plan::NodeFinished would have without taking the dyndep code path).
  for (vector<Edge*>::const_iterator oe = node->out_edges().begin();
       oe != node->out_edges().end(); ++oe) {
    map<Edge*, Want>::iterator want_e = want_.find(*oe);
    if (want_e == want_.end())
      continue;
    dyndep_walk.insert(want_e->first);
  }

  // See if any encountered edges are now ready.
  for (set<Edge*>::iterator wi = dyndep_walk.begin();
       wi != dyndep_walk.end(); ++wi) {
    map<Edge*, Want>::iterator want_e = want_.find(*wi);
    if (want_e == want_.end())
      continue;
    if (!EdgeMaybeReady(want_e, err))
      return false;
  }

  return true;
}

bool Plan::RefreshDyndepDependents(DependencyScan* scan, const Node* node,
                                   string* err) {
  // Collect the transitive closure of dependents and mark their edges
  // as not yet visited by RecomputeDirty.
  set<Node*> dependents;
  UnmarkDependents(node, &dependents);

  // Update the dirty state of all dependents and check if their edges
  // have become wanted.
  for (set<Node*>::iterator i = dependents.begin();
       i != dependents.end(); ++i) {
    Node* n = *i;

    // Check if this dependent node is now dirty.  Also checks for new cycles.
    std::vector<Node*> validation_nodes;
    if (!scan->RecomputeDirty(n, &validation_nodes, err))
      return false;

    // Add any validation nodes found during RecomputeDirty as new top level
    // targets.
    for (std::vector<Node*>::iterator v = validation_nodes.begin();
         v != validation_nodes.end(); ++v) {
      if (Edge* in_edge = (*v)->in_edge()) {
        if (!in_edge->outputs_ready() &&
            !AddTarget(*v, err)) {
          return false;
        }
      }
    }
    if (!n->dirty())
      continue;

    // This edge was encountered before.  However, we may not have wanted to
    // build it if the outputs were not known to be dirty.  With dyndep
    // information an output is now known to be dirty, so we want the edge.
    Edge* edge = n->in_edge();
    assert(edge && !edge->outputs_ready());
    map<Edge*, Want>::iterator want_e = want_.find(edge);
    assert(want_e != want_.end());
    if (want_e->second == kWantNothing) {
      want_e->second = kWantToStart;
      EdgeWanted(edge);
    }
  }
  return true;
}

void Plan::UnmarkDependents(const Node* node, set<Node*>* dependents) {
  for (vector<Edge*>::const_iterator oe = node->out_edges().begin();
       oe != node->out_edges().end(); ++oe) {
    Edge* edge = *oe;

    map<Edge*, Want>::iterator want_e = want_.find(edge);
    if (want_e == want_.end())
      continue;

    if (edge->mark_ != Edge::VisitNone) {
      edge->mark_ = Edge::VisitNone;
      for (vector<Node*>::iterator o = edge->outputs_.begin();
           o != edge->outputs_.end(); ++o) {
        if (dependents->insert(*o).second)
          UnmarkDependents(*o, dependents);
      }
    }
  }
}

namespace {

template <typename T>
struct SeenBefore {
  std::set<const T*>* seen_;

  SeenBefore(std::set<const T*>* seen) : seen_(seen) {}

  bool operator() (const T* item) {
    // Return true if the item has been seen before
    return !seen_->insert(item).second;
  }
};

// Heuristic for edge priority weighting.
// Phony edges are free (0 cost), all other edges are weighted equally.
int64_t EdgeWeightHeuristic(Edge *edge) {
  return edge->is_phony() ? 0 : 1;
}

}  // namespace

void Plan::ComputeCriticalPath() {
  METRIC_RECORD("ComputeCriticalPath");
  // Remove duplicate targets
  {
    std::set<const Node*> seen;
    SeenBefore<Node> seen_before(&seen);
    targets_.erase(std::remove_if(targets_.begin(), targets_.end(), seen_before),
                   targets_.end());
  }

  // Use backflow algorithm to compute the critical path for all
  // nodes, starting from the destination nodes.
  // XXX: ignores pools
  std::queue<Edge*> work_queue;        // Queue, for breadth-first traversal
  // The set of edges currently in work_queue, to avoid duplicates.
  std::set<const Edge*> active_edges;
  SeenBefore<Edge> seen_edge(&active_edges);

  for (size_t i = 0; i < targets_.size(); ++i) {
    const Node* target = targets_[i];
    if (Edge* in = target->in_edge()) {
      int64_t edge_weight = EdgeWeightHeuristic(in);
      in->set_critical_path_weight(
          std::max<int64_t>(edge_weight, in->critical_path_weight()));
      if (!seen_edge(in)) {
        work_queue.push(in);
      }
    }
  }

  while (!work_queue.empty()) {
    Edge* e = work_queue.front();
    work_queue.pop();
    // If the critical path of any dependent edges is updated, this
    // edge may need to be processed again. So re-allow insertion.
    active_edges.erase(e);

    for (std::vector<Node*>::iterator it = e->inputs_.begin(),
                                      end = e->inputs_.end();
         it != end; ++it) {
      Edge* in = (*it)->in_edge();
      if (!in) {
        continue;
      }
      // Only process edge if this node offers a higher weighted path
      const int64_t edge_weight = EdgeWeightHeuristic(in);
      const int64_t proposed_weight = e->critical_path_weight() + edge_weight;
      if (proposed_weight > in->critical_path_weight()) {
        in->set_critical_path_weight(proposed_weight);
        if (!seen_edge(in)) {
          work_queue.push(in);
        }
      }
    }
  }
}

void Plan::ScheduleInitialEdges() {
  // Add ready edges to queue.
  assert(ready_.empty());
  std::set<Pool*> pools;

  for (std::map<Edge*, Plan::Want>::iterator it = want_.begin(),
           end = want_.end(); it != end; ++it) {
    Edge* edge = it->first;
    Plan::Want want = it->second;
    if (!(want == kWantToStart && edge->AllInputsReady())) {
      continue;
    }

    Pool* pool = edge->pool();
    if (pool->ShouldDelayEdge()) {
      pool->DelayEdge(edge);
      pools.insert(pool);
    } else {
      ScheduleWork(it);
    }
  }

  // Call RetrieveReadyEdges only once at the end so higher priority
  // edges are retrieved first, not the ones that happen to be first
  // in the want_ map.
  for (std::set<Pool*>::iterator it=pools.begin(),
           end = pools.end(); it != end; ++it) {
    (*it)->RetrieveReadyEdges(&ready_);
  }
}

void Plan::PrepareQueue() {
  ComputeCriticalPath();
  ScheduleInitialEdges();
}

void Plan::Dump() const {
  printf("pending: %d\n", (int)want_.size());
  for (map<Edge*, Want>::const_iterator e = want_.begin(); e != want_.end(); ++e) {
    if (e->second != kWantNothing)
      printf("want ");
    e->first->Dump();
  }
  printf("ready: %d\n", (int)ready_.size());
}

struct RealCommandRunner : public CommandRunner {
  explicit RealCommandRunner(const BuildConfig& config) : config_(config) {}
  virtual ~RealCommandRunner() {}
  virtual size_t CanRunMore() const;
  virtual bool StartCommand(Edge* edge);
  virtual bool WaitForCommand(Result* result);
  virtual vector<Edge*> GetActiveEdges();
  virtual void Abort();

  const BuildConfig& config_;
  SubprocessSet subprocs_;
  map<const Subprocess*, Edge*> subproc_to_edge_;
};

vector<Edge*> RealCommandRunner::GetActiveEdges() {
  vector<Edge*> edges;
  for (map<const Subprocess*, Edge*>::iterator e = subproc_to_edge_.begin();
       e != subproc_to_edge_.end(); ++e)
    edges.push_back(e->second);
  return edges;
}

void RealCommandRunner::Abort() {
  subprocs_.Clear();
}

size_t RealCommandRunner::CanRunMore() const {
  size_t subproc_number =
      subprocs_.running_.size() + subprocs_.finished_.size();

  int64_t capacity = config_.parallelism - subproc_number;

  if (config_.max_load_average > 0.0f) {
    int load_capacity = config_.max_load_average - GetLoadAverage();
    if (load_capacity < capacity)
      capacity = load_capacity;
  }

  if (capacity < 0)
    capacity = 0;

  if (capacity == 0 && subprocs_.running_.empty())
    // Ensure that we make progress.
    capacity = 1;

  return capacity;
}

bool RealCommandRunner::StartCommand(Edge* edge) {
  string command = edge->EvaluateCommand();
  Subprocess* subproc = subprocs_.Add(command, edge->use_console());
  if (!subproc)
    return false;
  subproc_to_edge_.insert(make_pair(subproc, edge));

  return true;
}

bool RealCommandRunner::WaitForCommand(Result* result) {
  Subprocess* subproc;
  while ((subproc = subprocs_.NextFinished()) == NULL) {
    bool interrupted = subprocs_.DoWork();
    if (interrupted)
      return false;
  }

  result->status = subproc->Finish();
  result->output = subproc->GetOutput();

  map<const Subprocess*, Edge*>::iterator e = subproc_to_edge_.find(subproc);
  result->edge = e->second;
  subproc_to_edge_.erase(e);

  delete subproc;
  return true;
}

Builder::Builder(State* state, const BuildConfig& config,
                 BuildLog* build_log, DepsLog* deps_log,
                 DiskInterface* disk_interface, Status *status,
                 int64_t start_time_millis)
    : state_(state), config_(config), plan_(this), status_(status),
      start_time_millis_(start_time_millis), disk_interface_(disk_interface),
      scan_(state, build_log, deps_log, disk_interface,
            &config_.depfile_parser_options) {
  lock_file_path_ = ".ninja_lock";
  string build_dir = state_->bindings_.LookupVariable("builddir");
  if (!build_dir.empty())
    lock_file_path_ = build_dir + "/" + lock_file_path_;
}

Builder::~Builder() {
  Cleanup();
}

void Builder::Cleanup() {
  if (command_runner_.get()) {
    vector<Edge*> active_edges = command_runner_->GetActiveEdges();
    command_runner_->Abort();

    for (vector<Edge*>::iterator e = active_edges.begin();
         e != active_edges.end(); ++e) {
      string depfile = (*e)->GetUnescapedDepfile();
      for (vector<Node*>::iterator o = (*e)->outputs_.begin();
           o != (*e)->outputs_.end(); ++o) {
        // Only delete this output if it was actually modified.  This is
        // important for things like the generator where we don't want to
        // delete the manifest file if we can avoid it.  But if the rule
        // uses a depfile, always delete.  (Consider the case where we
        // need to rebuild an output because of a modified header file
        // mentioned in a depfile, and the command touches its depfile
        // but is interrupted before it touches its output file.)
        string err;
        TimeStamp new_mtime = disk_interface_->Stat((*o)->path(), &err);
        if (new_mtime == -1)  // Log and ignore Stat() errors.
          status_->Error("%s", err.c_str());
        if (!depfile.empty() || (*o)->mtime() != new_mtime)
          disk_interface_->RemoveFile((*o)->path());
      }
      if (!depfile.empty())
        disk_interface_->RemoveFile(depfile);
    }
  }

  string err;
  if (disk_interface_->Stat(lock_file_path_, &err) > 0)
    disk_interface_->RemoveFile(lock_file_path_);
}

Node* Builder::AddTarget(const string& name, string* err) {
  Node* node = state_->LookupNode(name);
  if (!node) {
    *err = "unknown target: '" + name + "'";
    return NULL;
  }
  if (!AddTarget(node, err))
    return NULL;
  return node;
}

bool Builder::AddTarget(Node* target, string* err) {
  std::vector<Node*> validation_nodes;
  if (!scan_.RecomputeDirty(target, &validation_nodes, err))
    return false;

  Edge* in_edge = target->in_edge();
  if (!in_edge || !in_edge->outputs_ready()) {
    if (!plan_.AddTarget(target, err)) {
      return false;
    }
  }

  // Also add any validation nodes found during RecomputeDirty as top level
  // targets.
  for (std::vector<Node*>::iterator n = validation_nodes.begin();
       n != validation_nodes.end(); ++n) {
    if (Edge* validation_in_edge = (*n)->in_edge()) {
      if (!validation_in_edge->outputs_ready() &&
          !plan_.AddTarget(*n, err)) {
        return false;
      }
    }
  }

  return true;
}

bool Builder::AlreadyUpToDate() const {
  return !plan_.more_to_do();
}

bool Builder::Build(string* err) {
  assert(!AlreadyUpToDate());
  plan_.PrepareQueue();

  int pending_commands = 0;
  int failures_allowed = config_.failures_allowed;

  // Set up the command runner if we haven't done so already.
  if (!command_runner_.get()) {
    if (config_.dry_run)
      command_runner_.reset(new DryRunCommandRunner);
    else
      command_runner_.reset(new RealCommandRunner(config_));
  }

  // We are about to start the build process.
  status_->BuildStarted();

  // This main loop runs the entire build process.
  // It is structured like this:
  // First, we attempt to start as many commands as allowed by the
  // command runner.
  // Second, we attempt to wait for / reap the next finished command.
  while (plan_.more_to_do()) {
    // See if we can start any more commands.
    if (failures_allowed) {
      size_t capacity = command_runner_->CanRunMore();
      while (capacity > 0) {
        Edge* edge = plan_.FindWork();
        if (!edge)
          break;

        if (edge->GetBindingBool("generator")) {
          scan_.build_log()->Close();
        }

        if (!StartEdge(edge, err)) {
          Cleanup();
          status_->BuildFinished();
          return false;
        }

        if (edge->is_phony()) {
          if (!plan_.EdgeFinished(edge, Plan::kEdgeSucceeded, err)) {
            Cleanup();
            status_->BuildFinished();
            return false;
          }
        } else {
          ++pending_commands;

          --capacity;

          // Re-evaluate capacity.
          size_t current_capacity = command_runner_->CanRunMore();
          if (current_capacity < capacity)
            capacity = current_capacity;
        }
      }

       // We are finished with all work items and have no pending
       // commands. Therefore, break out of the main loop.
       if (pending_commands == 0 && !plan_.more_to_do()) break;
    }

    // See if we can reap any finished commands.
    if (pending_commands) {
      CommandRunner::Result result;
      if (!command_runner_->WaitForCommand(&result) ||
          result.status == ExitInterrupted) {
        Cleanup();
        status_->BuildFinished();
        *err = "interrupted by user";
        return false;
      }

      --pending_commands;
      if (!FinishCommand(&result, err)) {
        Cleanup();
        status_->BuildFinished();
        return false;
      }

      if (!result.success()) {
        if (failures_allowed)
          failures_allowed--;
      }

      // We made some progress; start the main loop over.
      continue;
    }

    // If we get here, we cannot make any more progress.
    status_->BuildFinished();
    if (failures_allowed == 0) {
      if (config_.failures_allowed > 1)
        *err = "subcommands failed";
      else
        *err = "subcommand failed";
    } else if (failures_allowed < config_.failures_allowed)
      *err = "cannot make progress due to previous errors";
    else
      *err = "stuck [this is a bug]";

    return false;
  }

  status_->BuildFinished();
  return true;
}

bool Builder::StartEdge(Edge* edge, string* err) {
  METRIC_RECORD("StartEdge");
  if (edge->is_phony())
    return true;

  int64_t start_time_millis = GetTimeMillis() - start_time_millis_;
  running_edges_.insert(make_pair(edge, start_time_millis));

  status_->BuildEdgeStarted(edge, start_time_millis);

  TimeStamp build_start = -1;

  // Create directories necessary for outputs and remember the current
  // filesystem mtime to record later
  // XXX: this will block; do we care?
  for (vector<Node*>::iterator o = edge->outputs_.begin();
       o != edge->outputs_.end(); ++o) {
    if (!disk_interface_->MakeDirs((*o)->path()))
      return false;
    if (build_start == -1) {
      disk_interface_->WriteFile(lock_file_path_, "");
      build_start = disk_interface_->Stat(lock_file_path_, err);
      if (build_start == -1)
        build_start = 0;
    }
  }

  edge->command_start_time_ = build_start;

  // Create response file, if needed
  // XXX: this may also block; do we care?
  string rspfile = edge->GetUnescapedRspfile();
  if (!rspfile.empty()) {
    string content = edge->GetBinding("rspfile_content");
    if (!disk_interface_->WriteFile(rspfile, content))
      return false;
  }

  // start command computing and run it
  if (!command_runner_->StartCommand(edge)) {
    err->assign("command '" + edge->EvaluateCommand() + "' failed.");
    return false;
  }

  return true;
}

bool Builder::FinishCommand(CommandRunner::Result* result, string* err) {
  METRIC_RECORD("FinishCommand");

  Edge* edge = result->edge;

  // First try to extract dependencies from the result, if any.
  // This must happen first as it filters the command output (we want
  // to filter /showIncludes output, even on compile failure) and
  // extraction itself can fail, which makes the command fail from a
  // build perspective.
  vector<Node*> deps_nodes;
  string deps_type = edge->GetBinding("deps");
  const string deps_prefix = edge->GetBinding("msvc_deps_prefix");
  if (!deps_type.empty()) {
    string extract_err;
    if (!ExtractDeps(result, deps_type, deps_prefix, &deps_nodes,
                     &extract_err) &&
        result->success()) {
      if (!result->output.empty())
        result->output.append("\n");
      result->output.append(extract_err);
      result->status = ExitFailure;
    }
  }

  int64_t start_time_millis, end_time_millis;
  RunningEdgeMap::iterator it = running_edges_.find(edge);
  start_time_millis = it->second;
  end_time_millis = GetTimeMillis() - start_time_millis_;
  running_edges_.erase(it);

  status_->BuildEdgeFinished(edge, start_time_millis, end_time_millis,
                             result->success(), result->output);

  // The rest of this function only applies to successful commands.
  if (!result->success()) {
    return plan_.EdgeFinished(edge, Plan::kEdgeFailed, err);
  }

  // Restat the edge outputs
  TimeStamp record_mtime = 0;
  if (!config_.dry_run) {
    const bool restat = edge->GetBindingBool("restat");
    const bool generator = edge->GetBindingBool("generator");
    bool node_cleaned = false;
    record_mtime = edge->command_start_time_;

    // restat and generator rules must restat the outputs after the build
    // has finished. if record_mtime == 0, then there was an error while
    // attempting to touch/stat the temp file when the edge started and
    // we should fall back to recording the outputs' current mtime in the
    // log.
    if (record_mtime == 0 || restat || generator) {
      for (vector<Node*>::iterator o = edge->outputs_.begin();
           o != edge->outputs_.end(); ++o) {
        TimeStamp new_mtime = disk_interface_->Stat((*o)->path(), err);
        if (new_mtime == -1)
          return false;
        if (new_mtime > record_mtime)
          record_mtime = new_mtime;
        if ((*o)->mtime() == new_mtime && restat) {
          // The rule command did not change the output.  Propagate the clean
          // state through the build graph.
          // Note that this also applies to nonexistent outputs (mtime == 0).
          if (!plan_.CleanNode(&scan_, *o, err))
            return false;
          node_cleaned = true;
        }
      }
    }
    if (node_cleaned) {
      record_mtime = edge->command_start_time_;
    }
  }

  if (!plan_.EdgeFinished(edge, Plan::kEdgeSucceeded, err))
    return false;

  // Delete any left over response file.
  string rspfile = edge->GetUnescapedRspfile();
  if (!rspfile.empty() && !g_keep_rsp)
    disk_interface_->RemoveFile(rspfile);

  if (scan_.build_log()) {
    if (!scan_.build_log()->RecordCommand(edge, start_time_millis,
                                          end_time_millis, record_mtime)) {
      *err = string("Error writing to build log: ") + strerror(errno);
      return false;
    }
  }

  if (!deps_type.empty() && !config_.dry_run) {
    assert(!edge->outputs_.empty() && "should have been rejected by parser");
    for (std::vector<Node*>::const_iterator o = edge->outputs_.begin();
         o != edge->outputs_.end(); ++o) {
      TimeStamp deps_mtime = disk_interface_->Stat((*o)->path(), err);
      if (deps_mtime == -1)
        return false;
      if (!scan_.deps_log()->RecordDeps(*o, deps_mtime, deps_nodes)) {
        *err = std::string("Error writing to deps log: ") + strerror(errno);
        return false;
      }
    }
  }
  return true;
}

bool Builder::ExtractDeps(CommandRunner::Result* result,
                          const string& deps_type,
                          const string& deps_prefix,
                          vector<Node*>* deps_nodes,
                          string* err) {
  if (deps_type == "msvc") {
    CLParser parser;
    string output;
    if (!parser.Parse(result->output, deps_prefix, &output, err))
      return false;
    result->output = output;
    for (set<string>::iterator i = parser.includes_.begin();
         i != parser.includes_.end(); ++i) {
      // ~0 is assuming that with MSVC-parsed headers, it's ok to always make
      // all backslashes (as some of the slashes will certainly be backslashes
      // anyway). This could be fixed if necessary with some additional
      // complexity in IncludesNormalize::Relativize.
      deps_nodes->push_back(state_->GetNode(*i, ~0u));
    }
  } else if (deps_type == "gcc") {
    string depfile = result->edge->GetUnescapedDepfile();
    if (depfile.empty()) {
      *err = string("edge with deps=gcc but no depfile makes no sense");
      return false;
    }

    // Read depfile content.  Treat a missing depfile as empty.
    string content;
    switch (disk_interface_->ReadFile(depfile, &content, err)) {
    case DiskInterface::Okay:
      break;
    case DiskInterface::NotFound:
      err->clear();
      break;
    case DiskInterface::OtherError:
      return false;
    }
    if (content.empty())
      return true;

    DepfileParser deps(config_.depfile_parser_options);
    if (!deps.Parse(&content, err))
      return false;

    // XXX check depfile matches expected output.
    deps_nodes->reserve(deps.ins_.size());
    for (vector<StringPiece>::iterator i = deps.ins_.begin();
         i != deps.ins_.end(); ++i) {
      uint64_t slash_bits;
      CanonicalizePath(const_cast<char*>(i->str_), &i->len_, &slash_bits);
      deps_nodes->push_back(state_->GetNode(*i, slash_bits));
    }

    if (!g_keep_depfile) {
      if (disk_interface_->RemoveFile(depfile) < 0) {
        *err = string("deleting depfile: ") + strerror(errno) + string("\n");
        return false;
      }
    }
  } else {
    Fatal("unknown deps type '%s'", deps_type.c_str());
  }

  return true;
}

bool Builder::LoadDyndeps(Node* node, string* err) {
  status_->BuildLoadDyndeps();

  // Load the dyndep information provided by this node.
  DyndepFile ddf;
  if (!scan_.LoadDyndeps(node, &ddf, err))
    return false;

  // Update the build plan to account for dyndep modifications to the graph.
  if (!plan_.DyndepsLoaded(&scan_, node, ddf, err))
    return false;

  return true;
}