SAMRAI::tbox::Clock Struct Reference

#include <source/toolbox/timers/Clock.h>

List of all members.

Static Public Member Functions
static void	initialize (clock_t &clock)
static void	initialize (double &clock)
static void	timestamp (clock_t &user, clock_t &sys, clock_t &wall)
static void	timestamp (clock_t &user, clock_t &sys, double &wall)
static double	getClockCycle ()

---

Detailed Description

Class Clock serves as a single point of access for system clock information. System and user time are computed via the POSIX compliant times() function. This is described on p. 137, Lewine, POSIX programmers guide, 1992. The methods and structs used in this utility are defined in <sys/times.h>. Start and end times are stored as variables of type clock_t. A clock_t value can be converted to seconds by dividing by CLK_TCK (which is defined in <sys/times.h>). Different systems may use different CLK_TCK. Time is accessed by calling the times() function which takes as an argument a reference to an object of type struct tms. This object will record the system and user time (obj.tms_utime & obj.tms_stime) and will return the time since the system was started.

The return value from the call to times() can be used to compute elapsed wallclock time. Alternatively, one can use MPI_Wtime() if MPI libraries are included. Two methods are defined for accessing system time - one that has a clock_t struct argument for wallclock time (the non-MPI case) and one that has a double argument to record the value of MPI_Wtime().

Computing user/system/wallclock time with the times() function is performed as follows:

 *    struct tms buffer;
 *    clock_t wtime_start = times(&buffer);
 *    clock_t stime_start = buffer.tms_stime;
 *    clock_t utime_start = buffer.tms_utime;
 *     (do some computational work)
 *    clock_t wtime_stop  = times(&buffer);
 *    clock_t stime_stop  = buffer.tms_stime;
 *    clock_t utime_stop  = buffer.tms_utime;
 *    double wall_time   = double(wtime_stop-wtime_start)/double(CLK_TCK);
 *    double user_time   = double(utime_stop-utime_start)/double(CLK_TCK);
 *    double sys_time    = double(stime_stop-stime_start)/double(CLK_TCK);
 * 

---

Member Function Documentation

void SAMRAI::tbox::Clock::initialize (  clock_t &  clock  )  [static]

Initialize system clock. Argument must be in the "clock_t" format which is a standard POSIX struct provided on most systems in the <sys/times.h> include file. On Microsoft systems, it is provided in <time.h>.

void SAMRAI::tbox::Clock::initialize (  double &  clock  )  [static]

Initialize system clock, where clock is in double format.

void SAMRAI::tbox::Clock::timestamp (  clock_t &  user, clock_t &  sys, clock_t &  wall )  [static]

Timestamp clocks for user, system, and wallclock times.

void SAMRAI::tbox::Clock::timestamp (  clock_t &  user, clock_t &  sys, double &  wall )  [static]

Timestamp user, system, and walltime clocks. Wallclock argument is in double format since it will access wallclock times from MPI_Wtime() function.

double SAMRAI::tbox::Clock::getClockCycle (   )  [static]

Returns clock cycle for the system.

---

The documentation for this struct was generated from the following files:

• source/toolbox/timers/Clock.h
• source/toolbox/timers/Clock.C

---