11.3. Timing

We propose two timers: a basic timer (WallTimer) and a more advanced one (CycleTimer). These two classes work under Windows, Linux and MacOS. The Solver class uses by default a WallTimer internally.

Both timers are declared in the header base/timer.h.

11.3.1. Basic timer

This basic timer is defined by the WallTimer class. This class proposes the usual methods:

• void Start()
• void Stop()
• bool Reset()
• void Restart()
• bool IsRunning() const
• int64 GetInMs() const
• double Get() const

GetInMs() returns the elapsed time in milliseconds while Get() returns this time in seconds.

If you need even more precise timing, use the following method:

• static int64 GetTimeInMicroSeconds()

that returns the time in microseconds.

To measure the time, we query the system time and add or subtract the queried times.

Warning

Our timers measure the wall times.

To get the time in milliseconds, we use:

System	Function
Linux	gettimeofday()
Windows	clock()
MacOS	gettimeofday()

To get the time in microseconds, we use:

System	Function
Linux	clock_gettime()
Windows	QueryPerformanceCounter() and QueryPerformanceFrequency()
MacOS	mach_absolute_time() and mach_timebase_info()

What is the wall time?

The wall time is the real time that elapses from start to end of a program/task/process, including the time due to system delays (other programs running at the same time, waiting times for resources to become available, etc). In other words, it is the difference between the time at which a task finishes and the time at which the task started.

11.3.2. Advanced timer

This timer is defined by the CycleTimer class. Actually, the CycleTimer class uses... the WallTimer class internally. More precisely, the CycleTimer class is based on the static int64 GetTimeInMicroSeconds() method of the WallTimer class.

Its methods are

• void Reset()
• void Start()
• void Stop()
• int64 GetInUsec() const
• int64 GetInMs() const

GetInUsec() returns the elapsed time in microseconds and GetInMs() converts this time in milliseconds.

11.3.3. Integrated timer

The Solver class comes with an integrated timer. By default, this timer is a WallTimer (We use a typedef ClockTimer for a WallTimer).

This timer starts counting at the creation of the solver and is never reset.

Warning

The Solver‘s integrated timer is never reset!

To query this timer:

Solver solver(...);
LG << solver.wall_time()
                  << " ms elapsed since the creation of the solver";