Simplify running edges status

Store the number of running edges instead of trying to compute it
from the started and finshed edge counts, which may be different
for starting and ending status messages.  Allows removing the status
parameter to PrintStatus and the EdgeStatus enum.

src/build.cc

@@ -79,7 +79,7 @@ bool DryRunCommandRunner::WaitForCommand(Result* result) {
 
 BuildStatus::BuildStatus(const BuildConfig& config)
     : config_(config),
-      started_edges_(0), finished_edges_(0), total_edges_(0),
+      started_edges_(0), finished_edges_(0), total_edges_(0), running_edges_(0),
       time_millis_(0), progress_status_format_(NULL),
       current_rate_(config.parallelism) {
 
@@ -101,7 +101,7 @@ void BuildStatus::BuildEdgeStarted(Edge* edge, int64_t start_time_millis) {
   time_millis_ = start_time_millis;
 
   if (edge->use_console() || printer_.is_smart_terminal())
-    PrintStatus(edge, start_time_millis, kEdgeStarted);
+    PrintStatus(edge, start_time_millis);
 
   if (edge->use_console())
     printer_.SetConsoleLocked(true);
@@ -120,7 +120,12 @@ void BuildStatus::BuildEdgeFinished(Edge* edge, int64_t end_time_millis,
     return;
 
   if (!edge->use_console())
-    PrintStatus(edge, end_time_millis, kEdgeFinished);
+    PrintStatus(edge, end_time_millis);
+
+  // Update running_edges_ after PrintStatus so that the number of running
+  // edges doesn't oscillate between config.parallelism_ and
+  // config.parallelism_ - 1.
+  --running_edges_;
 
   // Print the command that is spewing before printing its output.
   if (!success) {
@@ -183,6 +188,9 @@ void BuildStatus::BuildLoadDyndeps() {
 }
 
 void BuildStatus::BuildStarted() {
+  started_edges_ = 0;
+  finished_edges_ = 0;
+  running_edges_ = 0;
 }
 
 void BuildStatus::BuildFinished() {
@@ -191,7 +199,7 @@ void BuildStatus::BuildFinished() {
 }
 
 string BuildStatus::FormatProgressStatus(
-    const char* progress_status_format, int64_t time, EdgeStatus status) const {
+    const char* progress_status_format, int64_t time) const {
   string out;
   char buf[32];
   for (const char* s = progress_status_format; *s != '\0'; ++s) {
@@ -216,11 +224,7 @@ string BuildStatus::FormatProgressStatus(
 
         // Running edges.
       case 'r': {
-        int running_edges = started_edges_ - finished_edges_;
-        // count the edge that just finished as a running edge
-        if (status == kEdgeFinished)
-          running_edges++;
-        snprintf(buf, sizeof(buf), "%d", running_edges);
+        snprintf(buf, sizeof(buf), "%d", running_edges_);
         out += buf;
         break;
       }
@@ -276,7 +280,7 @@ string BuildStatus::FormatProgressStatus(
   return out;
 }
 
-void BuildStatus::PrintStatus(Edge* edge, int64_t time, EdgeStatus status) {
+void BuildStatus::PrintStatus(Edge* edge, int64_t time) {
   if (config_.verbosity == BuildConfig::QUIET)
     return;
 
@@ -286,7 +290,7 @@ void BuildStatus::PrintStatus(Edge* edge, int64_t time, EdgeStatus status) {
   if (to_print.empty() || force_full_command)
     to_print = edge->GetBinding("command");
 
-  to_print = FormatProgressStatus(progress_status_format_, time, status) + to_print;
+  to_print = FormatProgressStatus(progress_status_format_, time) + to_print;
 
   printer_.Print(to_print,
                  force_full_command ? LinePrinter::FULL : LinePrinter::ELIDE);

src/build.h

@@ -252,25 +252,20 @@ struct BuildStatus {
   void BuildStarted();
   void BuildFinished();
 
-  enum EdgeStatus {
-    kEdgeStarted,
-    kEdgeFinished,
-  };
-
   /// Format the progress status string by replacing the placeholders.
   /// See the user manual for more information about the available
   /// placeholders.
   /// @param progress_status_format The format of the progress status.
   /// @param status The status of the edge.
-  string FormatProgressStatus(const char* progress_status_format, int64_t time,
-                              EdgeStatus status) const;
+  string FormatProgressStatus(const char* progress_status_format,
+                              int64_t time) const;
 
  private:
-  void PrintStatus(Edge* edge, int64_t time, EdgeStatus status);
+  void PrintStatus(Edge* edge, int64_t time);
 
   const BuildConfig& config_;
 
-  int started_edges_, finished_edges_, total_edges_;
+  int started_edges_, finished_edges_, total_edges_, running_edges_;
   int64_t time_millis_;
 
   /// Prints progress output.

src/build_test.cc

@@ -1384,8 +1384,7 @@ TEST_F(BuildWithLogTest, RestatTest) {
   ASSERT_EQ("", err);
   EXPECT_TRUE(builder_.Build(&err));
   ASSERT_EQ("", err);
-  EXPECT_EQ("[3/3]", builder_.status_->FormatProgressStatus("[%s/%t]", 0,
-      BuildStatus::kEdgeStarted));
+  EXPECT_EQ("[3/3]", builder_.status_->FormatProgressStatus("[%s/%t]", 0));
   command_runner_.commands_ran_.clear();
   state_.Reset();
 
@@ -1827,14 +1826,12 @@ TEST_F(BuildTest, StatusFormatElapsed) {
   status_.BuildStarted();
   // Before any task is done, the elapsed time must be zero.
   EXPECT_EQ("[%/e0.000]",
-            status_.FormatProgressStatus("[%%/e%e]", 0,
-                BuildStatus::kEdgeStarted));
+            status_.FormatProgressStatus("[%%/e%e]", 0));
 }
 
 TEST_F(BuildTest, StatusFormatReplacePlaceholder) {
   EXPECT_EQ("[%/s0/t0/r0/u0/f0]",
-            status_.FormatProgressStatus("[%%/s%s/t%t/r%r/u%u/f%f]", 0,
-                BuildStatus::kEdgeStarted));
+            status_.FormatProgressStatus("[%%/s%s/t%t/r%r/u%u/f%f]", 0));
 }
 
 TEST_F(BuildTest, FailedDepsParse) {