gdb: Use C++11 std::chrono

This patch fixes a few problems with GDB's time handling.

#1 - It avoids problems with gnulib's C++ namespace support

On MinGW, the struct timeval that should be passed to gnulib's
gettimeofday replacement is incompatible with libiberty's
timeval_sub/timeval_add.  That's because gnulib also replaces "struct
timeval" with its own definition, while libiberty expects the
system's.

E.g., in code like this:

  gettimeofday (&prompt_ended, NULL);
  timeval_sub (&prompt_delta, &prompt_ended, &prompt_started);
  timeval_add (&prompt_for_continue_wait_time,
               &prompt_for_continue_wait_time, &prompt_delta);

That's currently handled in gdb by not using gnulib's gettimeofday at
all (see common/gdb_sys_time.h), but that #undef hack won't work with
if/when we enable gnulib's C++ namespace support, because that mode
adds compile time warnings for uses of ::gettimeofday, which are hard
errors with -Werror.

#2 - But there's an elephant in the room: gettimeofday is not monotonic...

We're using it to:

  a) check how long functions take, for performance analysis
  b) compute when in the future to fire events in the event-loop
  c) print debug timestamps

But that's exactly what gettimeofday is NOT meant for.  Straight from
the man page:

~~~
       The time returned by gettimeofday() is affected by
       discontinuous jumps in the system time (e.g., if the system
       administrator manually changes the system time).  If you need a
       monotonically increasing clock, see clock_gettime(2).
~~~

std::chrono (part of the C++11 standard library) has a monotonic clock
exactly for such purposes (std::chrono::steady_clock).  This commit
switches to use that instead of gettimeofday, fixing all the issues
mentioned above.

gdb/ChangeLog:
2016-11-23  Pedro Alves  <palves@redhat.com>

	* Makefile.in (SFILES): Add common/run-time-clock.c.
	(HFILES_NO_SRCDIR): Add common/run-time-clock.h.
	(COMMON_OBS): Add run-time-clock.o.
	* common/run-time-clock.c, common/run-time-clock.h: New files.
	* defs.h (struct timeval, print_transfer_performance): Delete
	declarations.
	* event-loop.c (struct gdb_timer) <when>: Now a
	std::chrono::steady_clock::time_point.
	(create_timer): use std::chrono::steady_clock instead of
	gettimeofday.  Use new instead of malloc.
	(delete_timer): Use delete instead of xfree.
	(duration_cast_timeval): New.
	(update_wait_timeout): Use std::chrono::steady_clock instead of
	gettimeofday.
	* maint.c: Include <chrono> instead of "gdb_sys_time.h", <time.h>
	and "timeval-utils.h".
	(scoped_command_stats::~scoped_command_stats)
	(scoped_command_stats::scoped_command_stats): Use
	std::chrono::steady_clock instead of gettimeofday.  Use
	user_cpu_time_clock instead of get_run_time.
	* maint.h: Include "run-time-clock.h" and <chrono>.
	(scoped_command_stats): <m_start_cpu_time>: Now a
	user_cpu_time_clock::time_point.
	<m_start_wall_time>: Now a std::chrono::steady_clock::time_point.
	* mi/mi-main.c: Include "run-time-clock.h" and <chrono> instead of
	"gdb_sys_time.h" and <sys/resource.h>.
	(rusage): Delete.
	(mi_execute_command): Use new instead of XNEW.
	(mi_load_progress): Use std::chrono::steady_clock instead of
	gettimeofday.
	(timestamp): Rewrite in terms of std::chrono::steady_clock,
	user_cpu_time_clock and system_cpu_time_clock.
	(timeval_diff): Delete.
	(print_diff): Adjust to use std::chrono::steady_clock,
	user_cpu_time_clock and system_cpu_time_clock.
	* mi/mi-parse.h: Include "run-time-clock.h" and <chrono> instead
	of "gdb_sys_time.h".
	(struct mi_timestamp): Change fields types to
	std::chrono::steady_clock::time_point, user_cpu_time_clock::time
	and system_cpu_time_clock::time_point, instead of struct timeval.
	* symfile.c: Include <chrono> instead of <time.h> and
	"gdb_sys_time.h".
	(struct time_range): New.
	(generic_load): Use std::chrono::steady_clock instead of
	gettimeofday.
	(print_transfer_performance): Replace timeval parameters with a
	std::chrono::steady_clock::duration parameter.  Adjust.
	* utils.c: Include <chrono> instead of "timeval-utils.h",
	"gdb_sys_time.h", and <time.h>.
	(prompt_for_continue_wait_time): Now a
	std::chrono::steady_clock::duration.
	(defaulted_query, prompt_for_continue): Use
	std::chrono::steady_clock instead of
	gettimeofday/timeval_sub/timeval_add.
	(reset_prompt_for_continue_wait_time): Use
	std::chrono::steady_clock::duration instead of struct timeval.
	(get_prompt_for_continue_wait_time): Return a
	std::chrono::steady_clock::duration instead of struct timeval.
	(vfprintf_unfiltered): Use std::chrono::steady_clock instead of
	gettimeofday.  Use std::string.  Use '.' instead of ':'.
	* utils.h: Include <chrono>.
	(get_prompt_for_continue_wait_time): Return a
	std::chrono::steady_clock::duration instead of struct timeval.

gdb/gdbserver/ChangeLog:
2016-11-23  Pedro Alves  <palves@redhat.com>

	* debug.c: Include <chrono> instead of "gdb_sys_time.h".
	(debug_vprintf): Use std::chrono::steady_clock instead of
	gettimeofday.  Use '.' instead of ':'.
	* tracepoint.c: Include <chrono> instead of "gdb_sys_time.h".
	(get_timestamp): Use std::chrono::steady_clock instead of
	gettimeofday.

2 files changed, 25 insertions, 60 deletions

diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index 984a415..4d276c8 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -56,15 +56,8 @@
 #include "observer.h"
 
 #include <ctype.h>
-#include "gdb_sys_time.h"
-
-#if defined HAVE_SYS_RESOURCE_H
-#include <sys/resource.h>
-#endif
-
-#ifdef HAVE_GETRUSAGE
-struct rusage rusage;
-#endif
+#include "run-time-clock.h"
+#include <chrono>
 
 enum
   {
@@ -2169,7 +2162,7 @@ mi_execute_command (const char *cmd, int from_tty)
 
       if (do_timings)
 	{
-	  command->cmd_start = XNEW (struct mi_timestamp);
+	  command->cmd_start = new mi_timestamp ();
 	  timestamp (command->cmd_start);
 	}
 
@@ -2390,8 +2383,8 @@ mi_load_progress (const char *section_name,
 		  unsigned long total_sent,
 		  unsigned long grand_total)
 {
-  struct timeval time_now, delta, update_threshold;
-  static struct timeval last_update;
+  using namespace std::chrono;
+  static steady_clock::time_point last_update;
   static char *previous_sect_name = NULL;
   int new_section;
   struct ui_out *saved_uiout;
@@ -2416,19 +2409,6 @@ mi_load_progress (const char *section_name,
 
   uiout = current_uiout;
 
-  update_threshold.tv_sec = 0;
-  update_threshold.tv_usec = 500000;
-  gettimeofday (&time_now, NULL);
-
-  delta.tv_usec = time_now.tv_usec - last_update.tv_usec;
-  delta.tv_sec = time_now.tv_sec - last_update.tv_sec;
-
-  if (delta.tv_usec < 0)
-    {
-      delta.tv_sec -= 1;
-      delta.tv_usec += 1000000L;
-    }
-
   new_section = (previous_sect_name ?
 		 strcmp (previous_sect_name, section_name) : 1);
   if (new_section)
@@ -2451,13 +2431,12 @@ mi_load_progress (const char *section_name,
       gdb_flush (mi->raw_stdout);
     }
 
-  if (delta.tv_sec >= update_threshold.tv_sec &&
-      delta.tv_usec >= update_threshold.tv_usec)
+  steady_clock::time_point time_now = steady_clock::now ();
+  if (time_now - last_update > milliseconds (500))
     {
       struct cleanup *cleanup_tuple;
 
-      last_update.tv_sec = time_now.tv_sec;
-      last_update.tv_usec = time_now.tv_usec;
+      last_update = time_now;
       if (current_token)
 	fputs_unfiltered (current_token, mi->raw_stdout);
       fputs_unfiltered ("+download", mi->raw_stdout);
@@ -2480,23 +2459,10 @@ mi_load_progress (const char *section_name,
 static void
 timestamp (struct mi_timestamp *tv)
 {
-  gettimeofday (&tv->wallclock, NULL);
-#ifdef HAVE_GETRUSAGE
-  getrusage (RUSAGE_SELF, &rusage);
-  tv->utime.tv_sec = rusage.ru_utime.tv_sec;
-  tv->utime.tv_usec = rusage.ru_utime.tv_usec;
-  tv->stime.tv_sec = rusage.ru_stime.tv_sec;
-  tv->stime.tv_usec = rusage.ru_stime.tv_usec;
-#else
-  {
-    long usec = get_run_time ();
+  using namespace std::chrono;
 
-    tv->utime.tv_sec = usec/1000000L;
-    tv->utime.tv_usec = usec - 1000000L*tv->utime.tv_sec;
-    tv->stime.tv_sec = 0;
-    tv->stime.tv_usec = 0;
-  }
-#endif
+  tv->wallclock = steady_clock::now ();
+  run_time_clock::now (tv->utime, tv->stime);
 }
 
 static void
@@ -2517,23 +2483,20 @@ mi_print_timing_maybe (struct ui_file *file)
     print_diff_now (file, current_command_ts);
 }
 
-static long
-timeval_diff (struct timeval start, struct timeval end)
-{
-  return ((end.tv_sec - start.tv_sec) * 1000000L)
-    + (end.tv_usec - start.tv_usec);
-}
-
 static void
 print_diff (struct ui_file *file, struct mi_timestamp *start,
 	    struct mi_timestamp *end)
 {
+  using namespace std::chrono;
+
+  duration<double> wallclock = end->wallclock - start->wallclock;
+  duration<double> utime = end->utime - start->utime;
+  duration<double> stime = end->stime - start->stime;
+
   fprintf_unfiltered
     (file,
      ",time={wallclock=\"%0.5f\",user=\"%0.5f\",system=\"%0.5f\"}",
-     timeval_diff (start->wallclock, end->wallclock) / 1000000.0,
-     timeval_diff (start->utime, end->utime) / 1000000.0,
-     timeval_diff (start->stime, end->stime) / 1000000.0);
+     wallclock.count (), utime.count (), stime.count ());
 }
 
 void
diff --git a/gdb/mi/mi-parse.h b/gdb/mi/mi-parse.h
index d5595b3..dc8d21b 100644
--- a/gdb/mi/mi-parse.h
+++ b/gdb/mi/mi-parse.h
@@ -20,15 +20,17 @@
 #ifndef MI_PARSE_H
 #define MI_PARSE_H
 
-#include "gdb_sys_time.h"
+#include "run-time-clock.h"
+#include <chrono>
 
 /* MI parser */
 
 /* Timestamps for current command and last asynchronous command.  */
-struct mi_timestamp {
-  struct timeval wallclock;
-  struct timeval utime;
-  struct timeval stime;
+struct mi_timestamp
+{
+  std::chrono::steady_clock::time_point wallclock;
+  user_cpu_time_clock::time_point utime;
+  system_cpu_time_clock::time_point stime;
 };
 
 enum mi_command_type