Replace System.currentTimeMillis() by System.nanoTime()

[wilderrodrigues]

• System.nanoTime() is the best way to measure elapsed time in Java.
• It gives a resolution on the order of microseconds
• The System.currentTimeMillis() is used when calculating absolut time.

Add unit tests to cover negative cases

• Cover when the profile is not started/stopped

Test Environment

• Management Server: CentOS 7.1
• KVM

Tests successfully executed:

nosetests --with-marvin --marvin-config=/data/shared/marvin/mct-zone2-kvm2-ISOLATED.cfg -s -a tags=advanced,required_hardware=false
smoke/test_vm_life_cycle.py smoke/test_routers.py smoke/test_vpc_vpn.py smoke/test_reset_vm_on_reboot.py smoke/test_service_offerings.py
component/test_vpc_offerings.py smoke/test_privategw_acl.py smoke/test_network_acl.py

[asfbot]

cloudstack-pull-requests #629 SUCCESS
This pull request looks good

[DaanHoogland]

I'd use a new name for the var, like startTickInNanos (and of course stopTickInNanos)

[wilderrodrigues]

The nanoTime() is given in Microseconds. So, the MS still fits in.

Cheers,
Wilder

[wilderrodrigues]

Before we continue in a face-to-face chat, which would be better, just few point to take into account:

• The Profiler class is used as a profiler, to just measure how long a code took to be executed; used along with sleep calls - like a stop watch; and, still, as a monitor - there are lock implementations based on it. It makes the Profile class a profile, a stop-watch and a monitor.
• From a profiler perspective, do a Star, wait for 1 second, then a Stop and check how long it took to compute doesn't seem right to me.

The comments above are only related to the fact that the Profiler class is being exploited inside ACS.

Concerning the getDuration(). I agree that once it is taken into account to calculate milliseconds, it will be flaw.

In that case, it's too bad I trusted the existing test - which has a glitch in the assertion.

My suggestion is to refactor the getDuration(), renaming it into getDurationInMillis() and create a getDuration() which returns the nanotime - microseconds. The test has to be fixed as well.