If we are waiting for only one edge, print status for that edge

With this patch, should the build stall, it should be clear what edge is responsible.

The patch introduces BuildStatus::last_edge_status_ to keep track of the last edge we printed status for. This is to avoid printing status for the same edge twice, which is mainly when the output doesn’t overwrite previously printed output (non-smart terminal).

It would be better to delay re-printing status until we have waited a certain amount of time, which would also allow us to handle the case where more than one edge is stalling the build, but this require some refactoring, as waiting for tasks is presently done without the ability to specify a timeout.

src/build.cc

@@ -74,6 +74,7 @@ BuildStatus::BuildStatus(const BuildConfig& config)
     : config_(config),
       start_time_millis_(GetTimeMillis()),
       started_edges_(0), finished_edges_(0), total_edges_(0),
+      last_edge_status_(0),
       progress_status_format_(NULL),
       overall_rate_(), current_rate_(config.parallelism) {
 
@@ -98,6 +99,15 @@ void BuildStatus::BuildEdgeStarted(Edge* edge) {
   PrintStatus(edge);
 }
 
+void BuildStatus::PrintBuildEdgeStatus() {
+  if (running_edges_.size() == 1) {
+    Edge* running_edge = running_edges_.begin()->first;
+    if(last_edge_status_ != running_edge) {
+      PrintStatus(running_edge);
+    }
+  }
+}
+
 void BuildStatus::BuildEdgeFinished(Edge* edge,
                                     bool success,
                                     const string& output,
@@ -117,6 +127,9 @@ void BuildStatus::BuildEdgeFinished(Edge* edge,
   if (printer_.is_smart_terminal())
     PrintStatus(edge);
 
+  if (last_edge_status_ == edge)
+    last_edge_status_ = 0;
+
   // Print the command that is spewing before printing its output.
   if (!success)
     printer_.PrintOnNewLine("FAILED: " + edge->EvaluateCommand() + "\n");
@@ -248,6 +261,7 @@ void BuildStatus::PrintStatus(Edge* edge) {
 
   printer_.Print(to_print,
                  force_full_command ? LinePrinter::FULL : LinePrinter::ELIDE);
+  last_edge_status_ = edge;
 }
 
 Plan::Plan() : command_edges_(0), wanted_edges_(0) {}
@@ -630,6 +644,8 @@ bool Builder::Build(string* err) {
 
     // See if we can reap any finished commands.
     if (pending_commands) {
+      status_->PrintBuildEdgeStatus();
+
       CommandRunner::Result result;
       if (!command_runner_->WaitForCommand(&result) ||
           result.status == ExitInterrupted) {

src/build.h

@@ -196,6 +196,7 @@ struct BuildStatus {
   explicit BuildStatus(const BuildConfig& config);
   void PlanHasTotalEdges(int total);
   void BuildEdgeStarted(Edge* edge);
+  void PrintBuildEdgeStatus();
   void BuildEdgeFinished(Edge* edge, bool success, const string& output,
                          int* start_time, int* end_time);
   void BuildFinished();
@@ -219,6 +220,7 @@ struct BuildStatus {
   /// Map of running edge to time the edge started running.
   typedef map<Edge*, int> RunningEdgeMap;
   RunningEdgeMap running_edges_;
+  Edge* last_edge_status_;
 
   /// Prints progress output.
   LinePrinter printer_;