Re: [PATCH, v3] Potential solution to librt issue.

["Chris Fairles" <chris dot fairles at gmail dot com>]

On Thu, Jul 24, 2008 at 5:18 PM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
> Hi,
>
>> > Would it work *not* including <time.h> in chrono.cc,
>>
>> chrono.cc includes sys/time.h for gettimeofday not clock_gettime.
>> The clock_gettime comes through <time.h> in <ctime>.
>
> Sure, I know that. But my next messages clearly explain what I had in mind, the idea basically was that I wanted to hide the declaration of clock_gettime (available in <time.h> or <ctime>) to chrono.cc and replace it with one decorated with the weakref attribute. In fact, I discovered lately, that is not necessary, chrono.cc can certainly see the declarations in <time.h> and add a declaration of __clock_gettime on top, with weakref attribute and alias. Then use only the latter everywhere.
>
> The doubt now is the following: whether this structure in chrono.cc,  which is OK for safely delivering runtime error messages to the user, explaining which library is missing, as suggested by Martin, already a great improvement, would be still able to trigger the --as-needed mechanism in the specs of the compiler, which we want anyway in order to have the automatic on-demand linking.
>
> Paolo.
>
>

Ok. I'm a little in the dark here but I attached is a preliminary
patch anyway. I'm getting some unexpected behavior though. I've
removed the GLIBCXX_LIBS bits thus preventing the unconditional
inclusion of -lrt, BUT, when I compile a trivial app:

#include <chrono>
#include <iostream>
using namespace std;

int main()
{
  chrono::system_clock::time_point t = chrono::system_clock::now();
  cout << chrono::system_clock::period::den << endl;
  return 0;
}

with g++44 -O0 -std=gnu++0x -o test test.cpp

And its output is 1000000000 indicating nanosecond resolution which
means clock_gettime is being used. However "ldd test" shows:
libstdc++.so.6 => lib64/libstdc++.so.6
libm.so.6 => /lib64/tls/libm.so.6
libgcc_s.so.1 => lib64/libgcc_s.so.1
libc.so.6 => /lib64/tls/libc.so.6
/lib64/ld-linux-x86-64.so.2

So it works on my arch (x86_64) w/o librt and pthread... I must be
missing something.

Chris

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