Boost C++ Libraries: Ticket #1962: Doesn't measure wall clock time

attachment set

Dave Abrahams — Wed, 28 May 2008 00:23:46 GMT

attachment → thread4.cpp

r.jordans@… — Wed, 29 Oct 2008 09:53:23 GMT

The problem here is a generic one. The timer class uses clock() to measure time and this function is defined differently for Windows and Unix systems. On Windows it is defined as the wall clock time while on most Unix derivatives the total CPU time of the process is used.

A simple example: (test_clock.c) #include <time.h> #include <stdio.h> #include <unistd.h>

int main(int argc, char argv) {

time_t start = clock();

printf("Sleeping 1 second... "); fflush(stdout);

sleep(1);

printf("done\n"); printf("Time elapsed: %f\n", (clock()-start)/((float)CLOCKS_PER_SEC) );

return 0;

}

Will result in the following output: roel@localhost:~ $ ./test_clock Sleeping 1 second... done Time elapsed: 0.000000

Which is a completely different concept of time when compared to the result on Windows.

status changed; resolution set

Beman Dawes — Sat, 06 Jun 2009 12:02:01 GMT

status new → closed
resolution → wontfix

<timer.hpp> measures whatever time std::clock measures. Unfortunately, this varies from system to system.

The fix is to retire <timer.hpp>, and replace it with a much better set of facilities based on C++0x <chrono>.

I've been working on these facilities in svn.boost.org/svn/boost/sandbox/chrono

Currently, the header is <boost/chrono/timer.hpp>. It supplies:

process_clock: capturing real, user-CPU, and system-CPU clocks.
process_timer: capturing elapsed real, user-CPU, and system-CPU times.
run_timer: convenient reporting of process_timer results.

I'm probably going to move these to a new Boost.Timer library.

--Beman