Intel Threading Building Blocks

Chapter 8. Timing

Intel Threading Building Blocks provides a thread-safe and portable method to compute elapsed time.

Many operating systems provide a fine-grained method to track the accounting of central processing unit (CPU) time, and most provide a way to track elapsed/wall-clock time. The method of extracting an elapsed measurement with subsecond accuracy varies a great deal.

The class tick_count in Threading Building Blocks provides a simple interface for measuring wall-clock time, as shown in Example 8-1.

Example 8-1. Using tick_count to measure elapsed time

#include "tbb/tick_count.h"
using namespace tbb;
...
tick_count t0 = tick_count::now();
... do some work ...
tick_count t1 = tick_count::now();
printf("work took %g seconds\n",(t1-t0).seconds());

This is guaranteed to work even if the processor core running a task changes while the work is being done, and therefore the tick_count calls run on different processors.

Tip

Unlike some timing interfaces, tick_count is guaranteed to be safe to use across threads. It is based on a common or global clock. It is valid to subtract tick_count values that were created by different threads to compute elapsed time.

A tick_count value obtained from the static method tick_count::now() represents the current absolute time. This value has no meaning other than for use in comparisons with other tick_count values. Subtracting two tick_count values yields a relative time in tick_count::interval_t, as shown in Example 8-1. Relative time is expressed ...