View source for cpp/execution/scheduler

===Semantic requirements===
Given a scheduler of type {{tt|Sch}} and execution environment of type {{tt|Env}} such that {{c|sender_in<schedule_result_t<Sch>, Env>}} is satisfied, then {{c|/*sender-in-of*/<schedule_result_t<Sch>, Env>}} is modeled.

The scheduler's copy constructor, destructor, equality comparison, or swap member functions must be non-throwing.

All of those member functions as well as the scheduler type's {{tt|schedule}} function must be thread-safe.

Two schedulers are equal only if they represent the same execution resource.

For a given scheduler {{tt|sch}}, the expression {{c|get_completion_scheduler<set_value_t>(get_env(schedule(sch)))}} compares equal to {{tt|sch}}.

For a given scheduler {{tt|sch}}, if the expression {{c|get_domain(sch)}} is well-formed, then the expression {{c|get_domain(get_env(schedule(sch)))}} is also well-formed and has the same type.

The destructor of a scheduler must not block pending completion of any receivers connected to the sender objects returned from schedule (the underlying resource may provide a separate API to wait for completion of submitted function objects)