Track resource usage across the cluster. Created utility in utilities/ to track the total and the unused resources for each host in the cluster. Added utility to def/taskUtils.go to retrieve the resource requirement for a given taskID. Decoupled the code, to launch a list of tasks on a set of offerIDs, to schedulers/helpers.go and updated all the scheduling policies to call this function instead of directly calling mesos.SchedulerDriver#LaunchTasks. The resource availability of the cluster is updated at 2 stages -- 1. When the tasks are about to be launched (in schedulers/helpers.go#LaunchTasks), the scheduling policy switching logic will be able to adhere to the update in the resource availability due to the JUST launched tasks and 2. when a terminal status update is received for a task (in schedulers/base.go#statusUpdate).

def/task.go

@@ -36,6 +36,7 @@ func TasksFromJSON(uri string) ([]Task, error) {
 		return nil, errors.Wrap(err, "Error unmarshalling")
 	}
 
+	initTaskResourceRequirements(tasks)
 	return tasks, nil
 }
 

def/taskUtils.go

@@ -4,6 +4,8 @@ import (
 	"github.com/mash/gokmeans"
 	"log"
 	"sort"
+	"errors"
+	"fmt"
 )
 
 // Information about a cluster of tasks.
@@ -122,3 +124,38 @@ func SortTasks(ts []Task, sb sortBy) {
 		return sb(&ts[i]) <= sb(&ts[j])
 	})
 }
+
+// Map taskIDs to resource requirements.
+type TaskResources struct {
+	CPU   float64
+	Ram   float64
+	Watts float64
+}
+
+var taskResourceRequirement map[string]*TaskResources
+
+// Record resource requirements for all the tasks.
+func initTaskResourceRequirements(tasks []Task) {
+	taskResourceRequirement = make(map[string]*TaskResources)
+	baseTaskID := "electron-"
+	for _, task := range tasks {
+		for i := *task.Instances; i > 0; i-- {
+			taskID := fmt.Sprintf("%s-%d", baseTaskID + task.Name, *task.Instances)
+			taskResourceRequirement[taskID] = &TaskResources{
+				CPU: task.CPU,
+				Ram: task.RAM,
+				Watts: task.Watts,
+			}
+		}
+	}
+}
+
+// Retrieve the resource requirement of a task specified by the TaskID
+func GetResourceRequirement(taskID string) (TaskResources, error) {
+	if tr, ok := taskResourceRequirement[taskID]; ok {
+		return *tr, nil
+	} else {
+		// Shouldn't be here.
+		return TaskResources{}, errors.New("Invalid TaskID: " + taskID)
+	}
+}