Get system timestamp less often (only after sleeping/selecting)

src/util/Makefile.am

@@ -2,4 +2,4 @@ AM_CXXFLAGS = $(WARNING_CXXFLAGS) $(PICKY_CXXFLAGS) $(HARDEN_CFLAGS) $(MISC_CXXF
 
 noinst_LIBRARIES = libmoshutil.a
 
-libmoshutil_a_SOURCES = locale_utils.cc locale_utils.h swrite.cc swrite.h dos_assert.h fatal_assert.h select.h select.cc
+libmoshutil_a_SOURCES = locale_utils.cc locale_utils.h swrite.cc swrite.h dos_assert.h fatal_assert.h select.h select.cc timestamp.h timestamp.cc

src/util/select.h

@@ -39,6 +39,7 @@
 #include <sys/select.h>
 
 #include "fatal_assert.h"
+#include "timestamp.h"
 
 /* Convenience wrapper for pselect(2).
 
@@ -138,6 +139,8 @@ public:
       ret = 0;
     }
 
+    freeze_timestamp();
+
     return ret;
   }
 

src/util/timestamp.cc

@@ -0,0 +1,98 @@
+/*
+    Mosh: the mobile shell
+    Copyright 2012 Keith Winstein
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+    In addition, as a special exception, the copyright holders give
+    permission to link the code of portions of this program with the
+    OpenSSL library under certain conditions as described in each
+    individual source file, and distribute linked combinations including
+    the two.
+
+    You must obey the GNU General Public License in all respects for all
+    of the code used other than OpenSSL. If you modify file(s) with this
+    exception, you may extend this exception to your version of the
+    file(s), but you are not obligated to do so. If you do not wish to do
+    so, delete this exception statement from your version. If you delete
+    this exception statement from all source files in the program, then
+    also delete it here.
+*/
+
+#include "config.h"
+
+#include "timestamp.h"
+
+#include <errno.h>
+
+#if HAVE_CLOCK_GETTIME
+ #include <time.h>
+#elif HAVE_MACH_ABSOLUTE_TIME
+ #include <mach/mach_time.h>
+#elif HAVE_GETTIMEOFDAY
+ #include <sys/time.h>
+#endif
+
+static uint64_t millis_cache = -1;
+
+uint64_t frozen_timestamp( void )
+{
+  if ( millis_cache == uint64_t( -1 ) ) {
+    freeze_timestamp();
+  }
+
+  return millis_cache;
+}
+
+void freeze_timestamp( void )
+{
+#if HAVE_CLOCK_GETTIME
+  struct timespec tp;
+
+  if ( clock_gettime( CLOCK_MONOTONIC, &tp ) < 0 ) {
+    /* did not succeed */
+  } else {
+    uint64_t millis = tp.tv_nsec / 1000000;
+    millis += uint64_t( tp.tv_sec ) * 1000;
+
+    millis_cache = millis;
+    return;
+  }
+#elif HAVE_MACH_ABSOLUTE_TIME
+  static mach_timebase_info_data_t s_timebase_info;
+
+  if (s_timebase_info.denom == 0) {
+    mach_timebase_info(&s_timebase_info);
+  }
+
+  // NB: mach_absolute_time() returns "absolute time units"
+  // We need to apply a conversion to get milliseconds.
+  millis_cache = ((mach_absolute_time() * s_timebase_info.numer) / (1000000 * s_timebase_info.denom));
+  return;								    
+#elif HAVE_GETTIMEOFDAY
+  // NOTE: If time steps backwards, timeouts may be confused.
+  struct timeval tv;
+  if ( gettimeofday(&tv, NULL) ) {
+    perror( "gettimeofday" );
+  } else {
+    uint64_t millis = tv.tv_usec / 1000;
+    millis += uint64_t( tv.tv_sec ) * 1000;
+
+    millis_cache = millis;
+    return;
+  }
+#else
+# error "Don't know how to get a timestamp on this platform"
+#endif
+}

src/util/timestamp.h

@@ -0,0 +1,41 @@
+/*
+    Mosh: the mobile shell
+    Copyright 2012 Keith Winstein
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+    In addition, as a special exception, the copyright holders give
+    permission to link the code of portions of this program with the
+    OpenSSL library under certain conditions as described in each
+    individual source file, and distribute linked combinations including
+    the two.
+
+    You must obey the GNU General Public License in all respects for all
+    of the code used other than OpenSSL. If you modify file(s) with this
+    exception, you may extend this exception to your version of the
+    file(s), but you are not obligated to do so. If you do not wish to do
+    so, delete this exception statement from your version. If you delete
+    this exception statement from all source files in the program, then
+    also delete it here.
+*/
+
+#ifndef TIMESTAMP_HPP
+#define TIMESTAMP_HPP
+
+#include <stdint.h>
+
+void freeze_timestamp( void );
+uint64_t frozen_timestamp( void );
+
+#endif