[phobos] clock_gettime changes

[Jonathan M Davis]

On Saturday 20 November 2010 18:33:35 Brad Roberts wrote:
> I removed the -L-lrt from the auto-tester's dmd.conf file and it's still
> failing the phobos tests:
> 
> generated/linux/debug/unittest/std/datetime.o: In function
> `_D3std8datetime5Ticks12_staticCtor1OFNeZv':
> /home/braddr/sandbox/d/d-tester/client/3070/phobos-trunk/phobos/std/datetim
> e.d:80: undefined reference to `clock_getres'
> generated/linux/debug/unittest/std/datetime.o: In function
> `_D3std8datetime7systimeFNeZS3std8datetime5Ticks':
> /home/braddr/sandbox/d/d-tester/client/3070/phobos-trunk/phobos/std/datetim
> e.d:666: undefined reference to `clock_gettime'
> 
> The druntime tests do pass without linking against librt.
> 
> For now, adding librt back again so that the tests pass.

Well, the current version of std.datetime in Phobos checks whether 
clock_gettime() is available both for using clock_gettime() and for using 
clock_getres(). Both are in librt. Why std.datetime would try to use 
clock_getres() when clock_gettime() is unavailable, I don't know.

Really, the ideal situation is that clock_gettime(), clock_gettres(), etc. are 
available and used by the time code. That requires linking in librt. Without 
that, you cannot have a monotonic clock or a real time clock on Linux. This is 
particularly bad for StopWatch and benchmarking code, but it harms the accuracy 
of the time code in general. So, I really think that we should have 
clock_gettime() and clock_getres() in druntime with -L-lrt in the dmd.conf for 
Linux. Unfortunately, they aren't on the Mac, so the time code is going to have 
to use whatever the proper function calls are on the Mac, and clock_getttime() 
and company will have to be properly versioned so that MacOSX doesn't use them. 
But the Linux stuff needs them.

- Jonathan M Davis