IdleWakeups: optionally exit with target process

This change adds command-line option --stop-on-exit to IdleWakeups.
This makes IdleWakeups automatically stop measurement when the target
process closes, rather than needing to be stopped via Ctrl-C.

If the target process is not running when IdleWakeups starts, it runs
like normal until the target process is detected and then goes away,
at which point it stops.

Change-Id: Iaa11d79e13250c8887d7aacfbfde5d0696d76b08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464442Reviewed-by: Alex Gough <ajgo@chromium.org>
Commit-Queue: Jesse McKenna <jessemckenna@google.com>
Cr-Commit-Position: refs/heads/master@{#817043}

tools/win/IdleWakeups/README.md

@@ -27,8 +27,11 @@ median values over the entire measurement interval.
 By default, CPU usage is normalized to one CPU core, with 100% meaning one CPU
 core is fully utilized.
 
-To view CPU time in seconds rather than by percentage, use command-line option
-`--cpu-seconds`.
-
 [Intel Power Gadget](https://software.intel.com/en-us/articles/intel-power-gadget-20)
 is required to allow IdleWakeups tool to query power usage.
+
+Optional command-line flags:
+
+* `--cpu-seconds`: display CPU time in seconds rather than by percentage.
+
+* `--stop-on-exit`: stop measurement automatically when target process exits.
\ No newline at end of file

tools/win/IdleWakeups/idle_wakeups.cpp

@@ -289,17 +289,21 @@ int wmain(int argc, wchar_t* argv[]) {
   PowerSampler power_sampler;
   IdleWakeups the_app;
 
-  // Parse command line for target process name and optional --cpu-seconds flag.
+  // Parse command line for target process name and optional --cpu-seconds and
+  // --stop-on-exit flags.
   wchar_t* target_process_name = nullptr;
   bool cpu_usage_in_seconds = false;
+  bool stop_on_exit = false;
   for (int i = 1; i < argc; i++) {
     if (wcscmp(argv[i], L"--cpu-seconds") == 0)
       cpu_usage_in_seconds = true;
+    else if (wcscmp(argv[i], L"--stop-on-exit") == 0)
+      stop_on_exit = true;
     else if (!target_process_name)
       target_process_name = argv[i];
 
     // Stop parsing if all possible args have been found.
-    if (cpu_usage_in_seconds && target_process_name)
+    if (cpu_usage_in_seconds && stop_on_exit && target_process_name)
       break;
   }
   const char cpu_usage_unit = cpu_usage_in_seconds ? 's' : '%';
@@ -330,6 +334,7 @@ int wmain(int argc, wchar_t* argv[]) {
 
   PrintHeader();
 
+  bool target_process_seen = false;
   for (;;) {
     if (WaitForSingleObject(ctrl_c_pressed, sleep_time_sec * 1000) ==
         WAIT_OBJECT_0)
@@ -362,8 +367,11 @@ int wmain(int argc, wchar_t* argv[]) {
       cumulative_working_set += result.working_set;
       cumulative_energy += result.power;
       results.push_back(result);
+      target_process_seen = true;
     } else {
       num_idle_snapshots++;
+      if (stop_on_exit && target_process_seen)
+        break;
     }
   }