planner: add update functionality

Problem: when updating the Fluxion resource graph the `planner`
scheduled points' remaining resource count must be updated.

Add an `update` function to add or subtract from the current remaining
resource count at each scheduled point. Create a guard to ensure the
remaining count is nonnegative.

Author: milroy

resource/planner/c++/planner.cpp

@@ -229,6 +229,30 @@ int planner::restore_track_points ()
     return rc;
 }
 
+int planner::update_total (uint64_t resource_total)
+{
+    int64_t delta = resource_total - m_total_resources;
+    int64_t tmp = 0;
+    scheduled_point_t *point = nullptr;
+    if (delta == 0)
+        return 0;
+    m_total_resources = static_cast<int64_t> (resource_total);
+    point = m_sched_point_tree.get_state (m_plan_start);
+    while (point) {
+        // Prevent remaining from taking negative values. This should 
+        // reduce likelihood of errors when adding and removing spans.
+        // If the performance penalty is non-negligible we can 
+        // investigate letting remaining take negative values.
+        tmp = point->remaining + delta;
+        if (tmp >= 0)
+            point->remaining = tmp;
+        else
+            point->remaining = 0;
+        point = m_sched_point_tree.next (point);
+    }
+    return 0;
+}
+
 int64_t planner::get_total_resources () const
 {
     return m_total_resources;

resource/planner/c++/planner.hpp

@@ -51,6 +51,7 @@ class planner {
     int erase ();
     int reinitialize (int64_t base_time, uint64_t duration);
     int restore_track_points ();
+    int update_total (uint64_t resource_total);
 
     // Resources and duration
     int64_t get_total_resources () const;

resource/planner/c/planner.h

@@ -229,6 +229,19 @@ int64_t planner_span_resource_count (planner_t *ctx, int64_t span_id);
 */
 bool planners_equal (planner_t *lhs, planner_t *rhs);
 
+/*! Update the resource count to support elasticity.
+ *
+ *  \param ctx          opaque planner context returned from planner_new.
+ *  \param resource_total
+ *                      64-bit unsigned integer of
+ *                      the total count of available resources
+ *                      of the resource type.
+ *  \return             0 on success; -1 on an error with errno set as follows:
+ *                          EINVAL: invalid argument.
+ */
+int planner_update_total (planner_t *ctx,
+                          uint64_t resource_total);
+
 #ifdef __cplusplus
 }
 #endif

resource/planner/c/planner_c_interface.cpp

@@ -698,6 +698,12 @@ extern "C" bool planners_equal (planner_t *lhs, planner_t *rhs)
     return (*(lhs->plan) == *(rhs->plan));
 }
 
+extern "C" int planner_update_total (planner_t *ctx,
+                                     uint64_t resource_total)
+{
+    return ctx->plan->update_total (resource_total);
+}
+
 /*
  * vi: ts=4 sw=4 expandtab
  */