Joris Van Remoortere created MESOS-1991:
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Summary: Remove dynamic allocation from Option
Key: MESOS-1991
URL: https://issues.apache.org/jira/browse/MESOS-1991
Project: Mesos
Issue Type: Improvement
Components: stout
Reporter: Joris Van Remoortere
Assignee: Joris Van Remoortere
Priority: Minor
Remove dynamic allocations from Option class.
The motivation for this is 3-fold:
1. Reduce dynamic allocations. These can cause latency jitter as process
lifetime grows. This kind of jitter can make it hard to grasp the upper bound
of latency on certain operations under locks. This modification only moves the
allocated space of T, it does not reduce or increase the number of actual
construction / move calls unless the new move constructor is used.
2. The commonly understood implication of Optional / Option / Nullable is that
it augments the type field by 1 bit in order to allow representation of an
unknown or null state. This is handy in cases where a type such as int64_t
fully utilizes its 64 bit storage space, and representing unknown would
otherwise require us to steal a number (such as INT64_MAX). This class should
not take on the additional responsibility of managing memory for the augmented
type.
3. It can be very deceptive to a newcomer when Option<int64_t> does a dynamic
allocation. Intuitively you would not expect a type such as int64_t to do a
dynamic allocation or be expensive to copy. Naturally Option<BigType> would be
expected to be expensive to copy, and so a developer would be more inclined to
do something like std::shared_ptr<Option<BigType>>.
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