CTest: use std::chrono::steady_clock for time keeping

It was reported in issue #17345 that CTest does not use monotonic time
to report test duration. Monotonic clocks are not affected by large NTP
adjustments or things like daylight savings time.

As CMake 3.10 requires C++11, which introduced std::chrono, this commit
moves the time keeping in CTest from cmSystemTools::GetTime() to
std::chrono::steady_clock.

Fixes: #17345

1 files changed, 9 insertions, 5 deletions

diff --git a/Source/CTest/cmProcess.cxx b/Source/CTest/cmProcess.cxx
index f3c191b8a0..78dd59899b 100644
--- a/Source/CTest/cmProcess.cxx
+++ b/Source/CTest/cmProcess.cxx
@@ -3,8 +3,8 @@
 #include "cmProcess.h"
 
 #include "cmProcessOutput.h"
-#include "cmSystemTools.h"
 #include <iostream>
+#include <type_traits>
 
 cmProcess::cmProcess()
 {
@@ -13,7 +13,7 @@ cmProcess::cmProcess()
   this->TotalTime = 0;
   this->ExitValue = 0;
   this->Id = 0;
-  this->StartTime = 0;
+  this->StartTime = std::chrono::steady_clock::time_point();
 }
 
 cmProcess::~cmProcess()
@@ -35,7 +35,7 @@ bool cmProcess::StartProcess()
   if (this->Command.empty()) {
     return false;
   }
-  this->StartTime = cmSystemTools::GetTime();
+  this->StartTime = std::chrono::steady_clock::now();
   this->ProcessArgs.clear();
   // put the command as arg0
   this->ProcessArgs.push_back(this->Command.c_str());
@@ -143,7 +143,11 @@ int cmProcess::GetNextOutputLine(std::string& line, double timeout)
 
   // Record exit information.
   this->ExitValue = cmsysProcess_GetExitValue(this->Process);
-  this->TotalTime = cmSystemTools::GetTime() - this->StartTime;
+  this->TotalTime =
+    static_cast<double>(std::chrono::duration_cast<std::chrono::milliseconds>(
+                          std::chrono::steady_clock::now() - this->StartTime)
+                          .count()) /
+    1000.0;
   // Because of a processor clock scew the runtime may become slightly
   // negative. If someone changed the system clock while the process was
   // running this may be even more. Make sure not to report a negative
@@ -231,7 +235,7 @@ void cmProcess::ChangeTimeout(double t)
 void cmProcess::ResetStartTime()
 {
   cmsysProcess_ResetStartTime(this->Process);
-  this->StartTime = cmSystemTools::GetTime();
+  this->StartTime = std::chrono::steady_clock::now();
 }
 
 int cmProcess::GetExitException()