📝 Document scheduled_context constructor and methods

modules/schedulers.cppm

@@ -104,6 +104,22 @@ struct scheduled_context
   std::reference_wrapper<context> ctx;
   time_point wake_time = time_point::max();
 
+  /**
+   * @brief Construct a new scheduled context object.
+   *
+   * Initializes a scheduler entry by registering the unblock listener on the
+   * context and computing the initial wake deadline based on the context's
+   * current blocking state. If the context is time-blocked, the wake deadline
+   * is set to the current time plus the context's sleep duration. Otherwise,
+   * the wake deadline is set to time_point::max() (never).
+   *
+   * @param p_ctx The execution context to manage in the scheduler.
+   * @param p_listener Unblock listener to register on the context for
+   * notification when the context becomes ready to resume. May be nullptr if
+   * event-driven wakeup is not needed.
+   * @param p_clock Clock instance used to compute wake deadlines when
+   * the context is time-blocked.
+   */
   scheduled_context(async::context& p_ctx,
                     async::unblock_listener* p_listener,
                     Clock const& p_clock)
@@ -113,20 +129,19 @@ struct scheduled_context
     refresh(p_clock);
   }
 
-  // Bind this entry to p_ctx, register p_listener (may be nullptr), and
-  // compute the initial wake_time. Must be called exactly once before any
-  // other method.
-  void assign(async::context& p_ctx,
-              async::unblock_listener* p_listener,
-              Clock const& p_clock)
-  {
-    ctx = p_ctx;
-    p_ctx.on_unblock(p_listener);
-    refresh(p_clock);
-  }
-
-  // Recompute wake_time from the context's current sleep_time. Called after
-  // every resume because the blocking state may have changed.
+  /**
+   * @brief Recompute wake_time from the context's current blocking state.
+   *
+   * Updates the wake deadline based on the context's current blocking state.
+   * If the context is time-blocked, computes an absolute deadline by adding
+   * the context's sleep duration to the current time. Otherwise, sets the
+   * deadline to time_point::max() (never wake).
+   *
+   * Called after every context resume because the blocking state may have
+   * changed.
+   *
+   * @param p_clock Clock instance used to compute absolute wake times.
+   */
   void refresh(Clock const& p_clock)
   {
     if (ctx.get().state() == blocked_by::time) {
@@ -137,42 +152,75 @@ struct scheduled_context
   }
 
   /**
-   * @brief Resume the context if its deadline has elapsed or it is otherwise
-   * ready, then refresh wake_time to reflect the new state.
+   * @brief Recompute wake_time and update the soonest wake deadline.
    *
-   * @param p_clock - clock to get the current time from
-   * @return true - context was resumed
-   * @return false - context is done
+   * Refreshes the wake deadline from the context's current blocking state,
+   * then updates the global soonest wake deadline if this entry's deadline
+   * is earlier.
+   *
+   * Called after every context resume because the blocking state may have
+   * changed.
+   *
+   * @param p_clock Clock instance used to compute absolute wake times.
+   * @param p_soonest_time Reference to the global soonest wake deadline,
+   *                       updated if this entry's deadline is earlier.
    */
-  void resume(Clock const& p_clock)
+  void refresh(Clock const& p_clock, time_point& p_soonest_time)
   {
-    if (ctx.get().state() == blocked_by::time && wake_time <= p_clock.now()) {
+    refresh(p_clock);
+
+    if (wake_time < p_soonest_time) {
+      p_soonest_time = wake_time;
+    }
+  }
+
+  /**
+   * @brief Resume the context if its deadline has elapsed or it is ready,
+   * then refresh wake_time to reflect the new state.
+   *
+   * If the context is time-blocked and its deadline has elapsed, unblocks and
+   * resumes the context. Otherwise, if the context is ready (not blocked by
+   * time or I/O), resumes it immediately. After resuming, refreshes the wake
+   * deadline and updates the global soonest wake deadline.
+   *
+   * @param p_clock Clock instance used to get the current time and compute
+   *                wake deadlines.
+   * @param p_soonest_time Reference to the global soonest wake deadline,
+   *                       updated if this entry's deadline is earlier.
+   */
+  void resume(Clock const& p_clock, time_point& p_soonest_time)
+  {
+    if (ctx.get().state() == blocked_by::time and wake_time <= p_clock.now()) {
       // Deadline elapsed — unblock without triggering scheduler notification,
       // since we are the scheduler, then resume.
+      // We skip calling the unblock listener because this scheduler
       ctx.get().unblock_without_notification();
       ctx.get().resume();
       // Recompute after resume — state may have changed.
-      refresh(p_clock);
+      refresh(p_clock, p_soonest_time);
     } else if (is_ready()) {
       ctx.get().resume();
       // Recompute after resume — state may have changed.
-      refresh(p_clock);
+      refresh(p_clock, p_soonest_time);
     }
   }
 
-  // Returns true if the context is not blocked by time or I/O and can be
-  // resumed immediately.
+  /**
+   * @brief Check if the context is ready to resume immediately.
+   *
+   * Returns true if the context is not blocked by time or I/O, indicating
+   * it can be resumed without waiting for a deadline to elapse or for an
+   * external I/O event to complete.
+   *
+   * @return true if the context is not blocked by time or I/O.
+   * @return false if the context is blocked by time or I/O.
+   */
   [[nodiscard]] bool is_ready() const noexcept
   {
     return ctx.get().state() != blocked_by::io &&
            ctx.get().state() != blocked_by::time;
   }
 
-  [[nodiscard]] bool operator<(time_point const& p_other) const noexcept
-  {
-    return wake_time < p_other;
-  }
-
   // Clear the unblock listener so the context does not hold a pointer into
   // this stack frame after run_until_done_impl returns.
   ~scheduled_context()
@@ -224,30 +272,32 @@ void run_until_done_impl(
     bool can_sleep = true;
 
     for (auto& task : tasks) {
+      // Skip performing any of the following steps if the context is done
       if (task.ctx.get().done()) {
         continue;
       }
 
       all_done = false;
 
-      task.resume(p_clock);
-
-      // After resuming, re-evaluate whether we can sleep and what the
-      // soonest deadline is
-      if (task.wake_time < soonest_wake_time) {
-        soonest_wake_time = task.wake_time;
-      }
+      // This resumes the context if it is elidible to be resumed. It is
+      // elidible if it's wake time has expired or its in a pollable blocked by
+      // state. This function also updates the `soonest_wake_time` variable if
+      // this task could be awaken sooner than the previous.
+      task.resume(p_clock, soonest_wake_time);
 
+      // Before we move on to the next task, check if the task was blocked by
+      // something.
       if (task.is_ready()) {
         can_sleep = false;
       }
     }
 
+    // No more work needs to be done, this is how the scheduler exits.
     if (all_done) {
-      break;
+      return;
     }
 
-    if (can_sleep && soonest_wake_time < max_wake) {
+    if (can_sleep and soonest_wake_time < max_wake) {
       p_sleep_until(soonest_wake_time);
     }
   }