33 Execution control library [exec]

33.12 Execution contexts [exec.ctx]

33.12.1 execution​::​run_loop [exec.run.loop]

33.12.1.1 General [exec.run.loop.general]

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A run_loop is an execution resource on which work can be scheduled.
It maintains a thread-safe first-in-first-out queue of work.
Its run member function removes elements from the queue and executes them in a loop on the thread of execution that calls run.
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A run_loop instance has an associated count that corresponds to the number of work items that are in its queue.
Additionally, a run_loop instance has an associated state that can be one of starting, running, finishing, or finished.
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Concurrent invocations of the member functions of run_loop other than run and its destructor do not introduce data races.
The member functions pop-front, push-back, and finish execute atomically.
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Recommended practice: Implementations should use an intrusive queue of operation states to hold the work units to make scheduling allocation-free.
namespace std::execution { class run_loop { // [exec.run.loop.types], associated types class run-loop-scheduler; // exposition only class run-loop-sender; // exposition only struct run-loop-opstate-base { // exposition only virtual void execute() = 0; // exposition only run_loop* loop; // exposition only run-loop-opstate-base* next; // exposition only }; template<class Rcvr> using run-loop-opstate = unspecified; // exposition only // [exec.run.loop.members], member functions run-loop-opstate-base* pop-front(); // exposition only void push-back(run-loop-opstate-base*); // exposition only public: // [exec.run.loop.ctor], constructor and destructor run_loop() noexcept; run_loop(run_loop&&) = delete; ~run_loop(); // [exec.run.loop.members], member functions run-loop-scheduler get_scheduler(); void run(); void finish(); }; }