[OCC] Fix hang where abort channel blocks iterator (#379)

## Describe your changes and provide context
- instead of assuming one thing will arrive to the abort channel, drain
it
## Testing performed to validate your change
- new unit test captures situation (tests iterator)

tasks/scheduler.go

@@ -388,7 +388,6 @@ func (s *scheduler) prepareAndRunTask(wg *sync.WaitGroup, ctx sdk.Context, task
 	defer eSpan.End()
 	task.Ctx = eCtx
 
-	s.prepareTask(task)
 	s.executeTask(task)
 
 	s.DoValidate(func() {
@@ -441,27 +440,58 @@ func (s *scheduler) prepareTask(task *deliverTxTask) {
 	task.Ctx = ctx
 }
 
-// executeTask executes a single task
 func (s *scheduler) executeTask(task *deliverTxTask) {
-	dCtx, dSpan := s.traceSpan(task.Ctx, "SchedulerDeliverTx", task)
+	dCtx, dSpan := s.traceSpan(task.Ctx, "SchedulerExecuteTask", task)
 	defer dSpan.End()
 	task.Ctx = dCtx
 
-	resp := s.deliverTx(task.Ctx, task.Request)
+	s.prepareTask(task)
+
+	// Channel to signal the completion of deliverTx
+	doneCh := make(chan types.ResponseDeliverTx)
+
+	// Run deliverTx in a separate goroutine
+	go func() {
+		doneCh <- s.deliverTx(task.Ctx, task.Request)
+	}()
+
+	// Flag to mark if abort has happened
+	var abortOccurred bool
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	var abort *occ.Abort
+	// Drain the AbortCh in a non-blocking way
+	go func() {
+		defer wg.Done()
+		for abt := range task.AbortCh {
+			if !abortOccurred {
+				abortOccurred = true
+				abort = &abt
+			}
+		}
+	}()
+
+	// Wait for deliverTx to complete
+	resp := <-doneCh
 
 	close(task.AbortCh)
 
-	if abt, ok := <-task.AbortCh; ok {
+	wg.Wait()
+
+	// If abort has occurred, return, else set the response and status
+	if abortOccurred {
 		task.Status = statusAborted
-		task.Abort = &abt
+		task.Abort = abort
 		return
 	}
 
+	task.Status = statusExecuted
+	task.Response = &resp
+
 	// write from version store to multiversion stores
 	for _, v := range task.VersionStores {
 		v.WriteToMultiVersionStore()
 	}
-
-	task.Status = statusExecuted
-	task.Response = &resp
 }

tasks/scheduler_test.go

@@ -4,6 +4,9 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net/http"
+	_ "net/http/pprof"
+	"runtime"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -52,30 +55,106 @@ func initTestCtx(injectStores bool) sdk.Context {
 	return ctx
 }
 
+func generateTasks(count int) []*deliverTxTask {
+	var res []*deliverTxTask
+	for i := 0; i < count; i++ {
+		res = append(res, &deliverTxTask{Index: i})
+	}
+	return res
+}
+
 func TestProcessAll(t *testing.T) {
+	runtime.SetBlockProfileRate(1)
+
+	go func() {
+		http.ListenAndServe("localhost:6060", nil)
+	}()
+
 	tests := []struct {
 		name          string
 		workers       int
 		runs          int
+		before        func(ctx sdk.Context)
 		requests      []*sdk.DeliverTxEntry
 		deliverTxFunc mockDeliverTxFunc
 		addStores     bool
 		expectedErr   error
 		assertions    func(t *testing.T, ctx sdk.Context, res []types.ResponseDeliverTx)
 	}{
 		{
-			name:      "Test every tx accesses same key",
+			name:      "Test zero txs does not hang",
+			workers:   20,
+			runs:      10,
+			addStores: true,
+			requests:  requestList(0),
+			deliverTxFunc: func(ctx sdk.Context, req types.RequestDeliverTx) types.ResponseDeliverTx {
+				panic("should not deliver")
+			},
+			assertions: func(t *testing.T, ctx sdk.Context, res []types.ResponseDeliverTx) {
+				require.Len(t, res, 0)
+			},
+			expectedErr: nil,
+		},
+		{
+			name:      "Test tx writing to a store that another tx is iterating",
 			workers:   50,
-			runs:      50,
+			runs:      1,
+			requests:  requestList(500),
 			addStores: true,
-			requests:  requestList(100),
+			before: func(ctx sdk.Context) {
+				kv := ctx.MultiStore().GetKVStore(testStoreKey)
+				// initialize 100 test values in the base kv store so iterating isn't too fast
+				for i := 0; i < 10; i++ {
+					kv.Set([]byte(fmt.Sprintf("%d", i)), []byte(fmt.Sprintf("%d", i)))
+				}
+			},
+			deliverTxFunc: func(ctx sdk.Context, req types.RequestDeliverTx) types.ResponseDeliverTx {
+				kv := ctx.MultiStore().GetKVStore(testStoreKey)
+				if ctx.TxIndex()%2 == 0 {
+					// For even-indexed transactions, write to the store
+					kv.Set(req.Tx, req.Tx)
+					return types.ResponseDeliverTx{
+						Info: "write",
+					}
+				} else {
+					// For odd-indexed transactions, iterate over the store
+
+					// just write so we have more writes going on
+					kv.Set(req.Tx, req.Tx)
+					iterator := kv.Iterator(nil, nil)
+					defer iterator.Close()
+					for ; iterator.Valid(); iterator.Next() {
+						// Do nothing, just iterate
+					}
+					return types.ResponseDeliverTx{
+						Info: "iterate",
+					}
+				}
+			},
+			assertions: func(t *testing.T, ctx sdk.Context, res []types.ResponseDeliverTx) {
+				for idx, response := range res {
+					if idx%2 == 0 {
+						require.Equal(t, "write", response.Info)
+					} else {
+						require.Equal(t, "iterate", response.Info)
+					}
+				}
+			},
+			expectedErr: nil,
+		},
+		{
+			name:      "Test no overlap txs",
+			workers:   20,
+			runs:      10,
+			addStores: true,
+			requests:  requestList(1000),
 			deliverTxFunc: func(ctx sdk.Context, req types.RequestDeliverTx) types.ResponseDeliverTx {
 				// all txs read and write to the same key to maximize conflicts
 				kv := ctx.MultiStore().GetKVStore(testStoreKey)
-				val := string(kv.Get(itemKey))
 
 				// write to the store with this tx's index
-				kv.Set(itemKey, req.Tx)
+				kv.Set(req.Tx, req.Tx)
+				val := string(kv.Get(req.Tx))
 
 				// return what was read from the store (final attempt should be index-1)
 				return types.ResponseDeliverTx{
@@ -84,26 +163,22 @@ func TestProcessAll(t *testing.T) {
 			},
 			assertions: func(t *testing.T, ctx sdk.Context, res []types.ResponseDeliverTx) {
 				for idx, response := range res {
-					if idx == 0 {
-						require.Equal(t, "", response.Info)
-					} else {
-						// the info is what was read from the kv store by the tx
-						// each tx writes its own index, so the info should be the index of the previous tx
-						require.Equal(t, fmt.Sprintf("%d", idx-1), response.Info)
-					}
+					require.Equal(t, fmt.Sprintf("%d", idx), response.Info)
+				}
+				store := ctx.MultiStore().GetKVStore(testStoreKey)
+				for i := 0; i < len(res); i++ {
+					val := store.Get([]byte(fmt.Sprintf("%d", i)))
+					require.Equal(t, []byte(fmt.Sprintf("%d", i)), val)
 				}
-				// confirm last write made it to the parent store
-				latest := ctx.MultiStore().GetKVStore(testStoreKey).Get(itemKey)
-				require.Equal(t, []byte(fmt.Sprintf("%d", len(res)-1)), latest)
 			},
 			expectedErr: nil,
 		},
 		{
-			name:      "Test few workers many txs",
-			workers:   5,
-			runs:      10,
+			name:      "Test every tx accesses same key",
+			workers:   50,
+			runs:      1,
 			addStores: true,
-			requests:  requestList(50),
+			requests:  requestList(1000),
 			deliverTxFunc: func(ctx sdk.Context, req types.RequestDeliverTx) types.ResponseDeliverTx {
 				// all txs read and write to the same key to maximize conflicts
 				kv := ctx.MultiStore().GetKVStore(testStoreKey)
@@ -136,9 +211,9 @@ func TestProcessAll(t *testing.T) {
 		{
 			name:      "Test no stores on context should not panic",
 			workers:   50,
-			runs:      1,
+			runs:      10,
 			addStores: false,
-			requests:  requestList(50),
+			requests:  requestList(10),
 			deliverTxFunc: func(ctx sdk.Context, req types.RequestDeliverTx) types.ResponseDeliverTx {
 				return types.ResponseDeliverTx{
 					Info: fmt.Sprintf("%d", ctx.TxIndex()),
@@ -167,6 +242,10 @@ func TestProcessAll(t *testing.T) {
 				s := NewScheduler(tt.workers, ti, tt.deliverTxFunc)
 				ctx := initTestCtx(tt.addStores)
 
+				if tt.before != nil {
+					tt.before(ctx)
+				}
+
 				res, err := s.ProcessAll(ctx, tt.requests)
 				require.Len(t, res, len(tt.requests))