Timer: minor revisions

[kjbracey]

Summary of changes

• C++11-ify a little.
• Constify relevant methods. (already done in C++ Chrono support #12425)
• Make it copy/move constructible.
• Remove unneeded lock from destructor. (already done in C++ Chrono support #12425)

Impact of changes

Timer and LowPowerTimer are a little more flexible, and slightly optimised.

Migration actions required

n/a

Documentation

None

---

Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[X] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

---

Reviewers

---

[kjbracey]

The copy/move API extension stuff is a bit pointless, but it occurred to me while cleaning this up and after a comment about NonCopyable labelling that there is no particularly strong reason for this to be totally non-copyable. Maybe someone would find a use.

One use I can immediately imagine is sticking a Timer inside a functor passed to EventQueue to measure its dispatch time.

[ciarmcom]

@kjbracey-arm, thank you for your changes.
@ARMmbed/mbed-os-test @ARMmbed/mbed-os-core @ARMmbed/mbed-os-maintainers please review.

[evedon]

I don't know if it will be useful but the code change looks good.
PR description should be updated though as I can't see some of the minor revisions described.

[kjbracey]

PR description should be updated though as I can't see some of the minor revisions described.

Oh, guess it was parked a while, and there was a bit of rebasing. Some of those changes already happened in the Chrono work when TimerBase came in.

[0xc0170]

@kjbracey-arm Looking at the commit, it still has the old description - should be updated as well as Timer ? Please do and we can start CI later today.

Pull request has been modified.

[kjbracey]

Updated commit message. CI started.

[mbed-ci]

Test run: FAILED

Summary: 1 of 6 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_greentea-test

[kjbracey]

Reworked to pass tests, which apparently I'd failed to run on the final version.

Realised while doing it that we were missing the necessary locking on the copy constructor. Which turned out to be an interesting C++ exercise - answer found at https://www.justsoftwaresolutions.co.uk/threading/thread-safe-copy-constructors.html

In GCC at least those seem to compile to optimal code, fully inlining the locking and state copying into the copy constructor, with no visible overhead from the dummy parameters.

[adbridge]

@evedon @0xc0170 this needs a re-review please

[0xc0170]

I'll run CI meanwhile

[mbed-ci]

Test run: SUCCESS

Summary: 6 of 6 test jobs passed
Build number : 2
Build artifacts

[0xc0170]

Already approved, will merge now