From bc31c318b73b47a085551fc3a6fa70dba89dad28 Mon Sep 17 00:00:00 2001
From: Bruce Mitchener <bruce.mitchener@gmail.com>
Date: Sat, 2 Dec 2023 21:14:02 +0700
Subject: [PATCH] Use std::chrono::steady_clock for timers.

This improves portability by not using `gettimeofday()` or `clock()`.
---
 CMakeLists.txt               |  6 -----
 configure                    | 15 -------------
 gecode.m4                    |  6 -----
 gecode/support/config.hpp.in |  6 -----
 gecode/support/timer.hpp     | 43 ++++++------------------------------
 5 files changed, 7 insertions(+), 69 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8980604d52..6b4551ccc6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -213,12 +213,6 @@ endif ()
 
 include(CheckSymbolExists)
 check_symbol_exists(mmap sys/mman.h HAVE_MMAP)
-check_symbol_exists(gettimeofday sys/time.h HAVE_GETTIMEOFDAY)
-if (HAVE_GETTIMEOFDAY)
-  set(GECODE_USE_GETTIMEOFDAY 1)
-else ()
-  set(GECODE_USE_CLOCK 1)
-endif ()
 
 # Check for inline.
 include(CheckCSourceCompiles)
diff --git a/configure b/configure
index 71aaaae472..960c2d0770 100755
--- a/configure
+++ b/configure
@@ -6537,21 +6537,6 @@ $as_echo "no" >&6; }
 
 
 
-  ac_fn_cxx_check_header_mongrel "$LINENO" "sys/time.h" "ac_cv_header_sys_time_h" "$ac_includes_default"
-if test "x$ac_cv_header_sys_time_h" = xyes; then :
-
-$as_echo "#define GECODE_USE_GETTIMEOFDAY 1" >>confdefs.h
-
-else
-
-$as_echo "#define GECODE_USE_CLOCK 1" >>confdefs.h
-
-fi
-
-
-
-
-
 # Check whether --with-freelist32-size-max was given.
 if test "${with_freelist32_size_max+set}" = set; then :
   withval=$with_freelist32_size_max;
diff --git a/gecode.m4 b/gecode.m4
index dc31ee8d5b..68cf637f49 100755
--- a/gecode.m4
+++ b/gecode.m4
@@ -1519,12 +1519,6 @@ AC_DEFUN([AC_GECODE_THREADS],[
   fi
 ])
 
-AC_DEFUN([AC_GECODE_TIMER],[
-  AC_CHECK_HEADER(sys/time.h,
-  [AC_DEFINE(GECODE_USE_GETTIMEOFDAY,1,[Use gettimeofday for time-measurement])],
-  [AC_DEFINE(GECODE_USE_CLOCK,1,[Use clock() for time-measurement])])
-])
-
 dnl check whether we have suifficiently recent versions of flex/bison
 AC_DEFUN([AC_GECODE_FLEXBISON],
   [AC_CHECK_TOOL(HAVEFLEX, flex)
diff --git a/gecode/support/config.hpp.in b/gecode/support/config.hpp.in
index 88a8e020bd..4ccee0f761 100644
--- a/gecode/support/config.hpp.in
+++ b/gecode/support/config.hpp.in
@@ -114,12 +114,6 @@
 /* Whether to use unfair mutexes on macOS */
 #undef GECODE_USE_OSX_UNFAIR_MUTEX
 
-/* Use clock() for time-measurement */
-#undef GECODE_USE_CLOCK
-
-/* Use gettimeofday for time-measurement */
-#undef GECODE_USE_GETTIMEOFDAY
-
 /* Gecode version */
 #undef GECODE_VERSION
 
diff --git a/gecode/support/timer.hpp b/gecode/support/timer.hpp
index cc1e224601..85f9f91b40 100644
--- a/gecode/support/timer.hpp
+++ b/gecode/support/timer.hpp
@@ -31,13 +31,7 @@
  *
  */
 
-#ifdef GECODE_USE_GETTIMEOFDAY
-#include <sys/time.h>
-#endif
-
-#ifdef GECODE_USE_CLOCK
-#include <ctime>
-#endif
+#include <chrono>
 
 namespace Gecode { namespace Support {
 
@@ -50,11 +44,9 @@ namespace Gecode { namespace Support {
    */
   class GECODE_SUPPORT_EXPORT Timer {
   private:
-#if   defined(GECODE_USE_GETTIMEOFDAY)
-    timeval t0; ///< Start time
-#elif defined(GECODE_USE_CLOCK)
-    clock_t t0; ///< Start time
-#endif
+    using time_point = std::chrono::time_point<std::chrono::steady_clock>;
+    time_point t0; ///< Start time
+
   public:
     /// Start timer
     void start(void);
@@ -64,34 +56,13 @@ namespace Gecode { namespace Support {
 
   inline void
   Timer::start(void) {
-#if   defined(GECODE_USE_GETTIMEOFDAY)
-    if (gettimeofday(&t0, nullptr))
-      throw OperatingSystemError("Timer::start[gettimeofday]");
-#elif defined(GECODE_USE_CLOCK)
-    t0 = clock();
-#endif
+    t0 = std::chrono::steady_clock::now();
   }
 
   inline double
   Timer::stop(void) {
-#if   defined(GECODE_USE_GETTIMEOFDAY)
-    timeval t1, t;
-    if (gettimeofday(&t1, nullptr))
-      throw OperatingSystemError("Timer::stop[gettimeofday]");
-
-    // t = t1 - t2
-    t.tv_sec = t1.tv_sec - t0.tv_sec;
-    t.tv_usec = t1.tv_usec - t0.tv_usec;
-    if (t.tv_usec < 0) {
-      t.tv_sec--;
-      t.tv_usec += 1000000;
-    }
-
-    return (static_cast<double>(t.tv_sec) * 1000.0) +
-      (static_cast<double>(t.tv_usec)/1000.0);
-#elif defined(GECODE_USE_CLOCK)
-    return (static_cast<double>(clock()-t0) / CLOCKS_PER_SEC) * 1000.0;
-#endif
+    std::chrono::duration<double, std::milli> duration = std::chrono::steady_clock::now() - t0;
+    return duration.count();
   }
 
 }}