refactor: Separate TaskPool abstraction from Scheduler

common/task/interface.go

@@ -40,6 +40,25 @@ type (
 		TrySubmit(task PriorityTask) (bool, error)
 	}
 
+	// TaskPool manages task storage and determines scheduling order.
+	// Different implementations provide different scheduling algorithms.
+	TaskPool interface {
+		common.Daemon
+
+		// Submit adds a task to the pool, blocks if pool is full
+		Submit(task PriorityTask) error
+
+		// TrySubmit attempts to add a task, returns immediately if pool is full
+		TrySubmit(task PriorityTask) (bool, error)
+
+		// GetNextTask retrieves the next task according to the pool's scheduling algorithm
+		// Returns (task, true) if a task is available, (nil, false) if no task is ready
+		GetNextTask() (PriorityTask, bool)
+
+		// Len returns the number of tasks currently in the pool
+		Len() int
+	}
+
 	// SchedulerType respresents the type of the task scheduler implementation
 	SchedulerType int
 

common/task/weighted_channel_pool.go

@@ -83,7 +83,7 @@ func NewWeightedRoundRobinChannelPool[K comparable, V any](
 	timeSource clock.TimeSource,
 	options WeightedRoundRobinChannelPoolOptions,
 ) *WeightedRoundRobinChannelPool[K, V] {
-	return &WeightedRoundRobinChannelPool[K, V]{
+	wrr := &WeightedRoundRobinChannelPool[K, V]{
 		bufferSize:              options.BufferSize,
 		idleChannelTTLInSeconds: options.IdleChannelTTLInSeconds,
 		logger:                  logger,
@@ -92,6 +92,8 @@ func NewWeightedRoundRobinChannelPool[K comparable, V any](
 		channelMap:              make(map[K]*weightedChannel[V]),
 		shutdownCh:              make(chan struct{}),
 	}
+	wrr.iwrrSchedule.Store(make([]chan V, 0))
+	return wrr
 }
 
 func (p *WeightedRoundRobinChannelPool[K, V]) Start() {

common/task/weighted_round_robin_task_pool.go

@@ -0,0 +1,222 @@
+// Copyright (c) 2020 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package task
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+
+	"github.com/uber/cadence/common"
+	"github.com/uber/cadence/common/clock"
+	"github.com/uber/cadence/common/log"
+	"github.com/uber/cadence/common/metrics"
+)
+
+type weightedRoundRobinTaskPool[K comparable] struct {
+	sync.Mutex
+	status        int32
+	pool          *WeightedRoundRobinChannelPool[K, PriorityTask]
+	ctx           context.Context
+	cancel        context.CancelFunc
+	options       *WeightedRoundRobinTaskPoolOptions[K]
+	logger        log.Logger
+	taskCount     atomic.Int64        // O(1) task count tracking
+	schedule      []chan PriorityTask // Current schedule
+	scheduleIndex int                 // Current position in schedule
+}
+
+// NewWeightedRoundRobinTaskPool creates a new WRR task pool
+func NewWeightedRoundRobinTaskPool[K comparable](
+	logger log.Logger,
+	metricsClient metrics.Client,
+	timeSource clock.TimeSource,
+	options *WeightedRoundRobinTaskPoolOptions[K],
+) TaskPool {
+	metricsScope := metricsClient.Scope(metrics.TaskSchedulerScope)
+	ctx, cancel := context.WithCancel(context.Background())
+
+	pool := &weightedRoundRobinTaskPool[K]{
+		status: common.DaemonStatusInitialized,
+		pool: NewWeightedRoundRobinChannelPool[K, PriorityTask](
+			logger,
+			metricsScope,
+			timeSource,
+			WeightedRoundRobinChannelPoolOptions{
+				BufferSize:              options.QueueSize,
+				IdleChannelTTLInSeconds: defaultIdleChannelTTLInSeconds,
+			}),
+		ctx:     ctx,
+		cancel:  cancel,
+		options: options,
+		logger:  logger,
+	}
+
+	return pool
+}
+
+func (p *weightedRoundRobinTaskPool[K]) Start() {
+	if !atomic.CompareAndSwapInt32(&p.status, common.DaemonStatusInitialized, common.DaemonStatusStarted) {
+		return
+	}
+
+	p.pool.Start()
+
+	p.logger.Info("Weighted round robin task pool started.")
+}
+
+func (p *weightedRoundRobinTaskPool[K]) Stop() {
+	if !atomic.CompareAndSwapInt32(&p.status, common.DaemonStatusStarted, common.DaemonStatusStopped) {
+		return
+	}
+
+	p.cancel()
+	p.pool.Stop()
+
+	// Drain all tasks and nack them, updating the counter
+	taskChs := p.pool.GetAllChannels()
+	for _, taskCh := range taskChs {
+		p.drainAndNackTasks(taskCh)
+	}
+
+	p.logger.Info("Weighted round robin task pool stopped.")
+}
+
+func (p *weightedRoundRobinTaskPool[K]) Submit(task PriorityTask) error {
+	if p.isStopped() {
+		return ErrTaskSchedulerClosed
+	}
+
+	key := p.options.TaskToChannelKeyFn(task)
+	weight := p.options.ChannelKeyToWeightFn(key)
+
+	// Reject tasks with weight 0 - they won't be in the schedule
+	if weight <= 0 {
+		return ErrTaskWeightZero
+	}
+
+	taskCh, releaseFn := p.pool.GetOrCreateChannel(key, weight)
+	defer releaseFn()
+
+	select {
+	case taskCh <- task:
+		p.taskCount.Add(1)
+		if p.isStopped() {
+			p.drainAndNackTasks(taskCh)
+		}
+		return nil
+	case <-p.ctx.Done():
+		return ErrTaskSchedulerClosed
+	}
+}
+
+func (p *weightedRoundRobinTaskPool[K]) TrySubmit(task PriorityTask) (bool, error) {
+	if p.isStopped() {
+		return false, ErrTaskSchedulerClosed
+	}
+
+	key := p.options.TaskToChannelKeyFn(task)
+	weight := p.options.ChannelKeyToWeightFn(key)
+
+	// Reject tasks with weight 0 - they won't be in the schedule
+	if weight <= 0 {
+		return false, ErrTaskWeightZero
+	}
+
+	taskCh, releaseFn := p.pool.GetOrCreateChannel(key, weight)
+	defer releaseFn()
+
+	select {
+	case taskCh <- task:
+		p.taskCount.Add(1)
+		if p.isStopped() {
+			p.drainAndNackTasks(taskCh)
+		}
+		return true, nil
+	case <-p.ctx.Done():
+		return false, ErrTaskSchedulerClosed
+	default:
+		return false, nil
+	}
+}
+
+func (p *weightedRoundRobinTaskPool[K]) GetNextTask() (PriorityTask, bool) {
+	if p.isStopped() || p.Len() == 0 {
+		return nil, false
+	}
+
+	p.Lock()
+	defer p.Unlock()
+
+	// Get a fresh schedule if we don't have one or if we've reached the end
+	if p.schedule == nil || p.scheduleIndex >= len(p.schedule) {
+		p.schedule = p.pool.GetSchedule()
+		p.scheduleIndex = 0
+		if len(p.schedule) == 0 {
+			return nil, false
+		}
+	}
+
+	for p.Len() > 0 {
+		select {
+		case task := <-p.schedule[p.scheduleIndex]:
+			// Found a task, advance index and return
+			p.scheduleIndex++
+			p.taskCount.Add(-1)
+			return task, true
+		case <-p.ctx.Done():
+			return nil, false
+		default:
+			// No task in this channel, try next
+			p.scheduleIndex++
+
+			// If we've reached the end, get a fresh schedule and continue
+			if p.scheduleIndex >= len(p.schedule) {
+				p.schedule = p.pool.GetSchedule()
+				p.scheduleIndex = 0
+				if len(p.schedule) == 0 {
+					return nil, false
+				}
+			}
+		}
+	}
+	return nil, false
+}
+
+func (p *weightedRoundRobinTaskPool[K]) Len() int {
+	return int(p.taskCount.Load())
+}
+
+func (p *weightedRoundRobinTaskPool[K]) drainAndNackTasks(taskCh <-chan PriorityTask) {
+	for {
+		select {
+		case task := <-taskCh:
+			p.taskCount.Add(-1)
+			task.Nack(nil)
+		default:
+			return
+		}
+	}
+}
+
+func (p *weightedRoundRobinTaskPool[K]) isStopped() bool {
+	return atomic.LoadInt32(&p.status) == common.DaemonStatusStopped
+}