Merge pull request #744 from azavorotnii/ctx_cancel

Fix context cancellation racy handling

sqlite3.go

@@ -328,7 +328,7 @@ type SQLiteRows struct {
 	decltype []string
 	cls      bool
 	closed   bool
-	done     chan struct{}
+	ctx      context.Context // no better alternative to pass context into Next() method
 }
 
 type functionInfo struct {
@@ -1847,22 +1847,7 @@ func (s *SQLiteStmt) query(ctx context.Context, args []namedValue) (driver.Rows,
 		decltype: nil,
 		cls:      s.cls,
 		closed:   false,
-		done:     make(chan struct{}),
-	}
-
-	if ctxdone := ctx.Done(); ctxdone != nil {
-		go func(db *C.sqlite3) {
-			select {
-			case <-ctxdone:
-				select {
-				case <-rows.done:
-				default:
-					C.sqlite3_interrupt(db)
-					rows.Close()
-				}
-			case <-rows.done:
-			}
-		}(s.c.db)
+		ctx:      ctx,
 	}
 
 	return rows, nil
@@ -1890,29 +1875,43 @@ func (s *SQLiteStmt) Exec(args []driver.Value) (driver.Result, error) {
 	return s.exec(context.Background(), list)
 }
 
+// exec executes a query that doesn't return rows. Attempts to honor context timeout.
 func (s *SQLiteStmt) exec(ctx context.Context, args []namedValue) (driver.Result, error) {
+	if ctx.Done() == nil {
+		return s.execSync(args)
+	}
+
+	type result struct {
+		r   driver.Result
+		err error
+	}
+	resultCh := make(chan result)
+	go func() {
+		r, err := s.execSync(args)
+		resultCh <- result{r, err}
+	}()
+	select {
+	case rv := <- resultCh:
+		return rv.r, rv.err
+	case <-ctx.Done():
+		select {
+		case <-resultCh: // no need to interrupt
+		default:
+			// this is still racy and can be no-op if executed between sqlite3_* calls in execSync.
+			C.sqlite3_interrupt(s.c.db)
+			<-resultCh // ensure goroutine completed
+		}
+		return nil, ctx.Err()
+	}
+}
+
+func (s *SQLiteStmt) execSync(args []namedValue) (driver.Result, error) {
 	if err := s.bind(args); err != nil {
 		C.sqlite3_reset(s.s)
 		C.sqlite3_clear_bindings(s.s)
 		return nil, err
 	}
 
-	if ctxdone := ctx.Done(); ctxdone != nil {
-		done := make(chan struct{})
-		defer close(done)
-		go func(db *C.sqlite3) {
-			select {
-			case <-done:
-			case <-ctxdone:
-				select {
-				case <-done:
-				default:
-					C.sqlite3_interrupt(db)
-				}
-			}
-		}(s.c.db)
-	}
-
 	var rowid, changes C.longlong
 	rv := C._sqlite3_step_row_internal(s.s, &rowid, &changes)
 	if rv != C.SQLITE_ROW && rv != C.SQLITE_OK && rv != C.SQLITE_DONE {
@@ -1933,9 +1932,6 @@ func (rc *SQLiteRows) Close() error {
 		return nil
 	}
 	rc.closed = true
-	if rc.done != nil {
-		close(rc.done)
-	}
 	if rc.cls {
 		rc.s.mu.Unlock()
 		return rc.s.Close()
@@ -1979,13 +1975,39 @@ func (rc *SQLiteRows) DeclTypes() []string {
 	return rc.declTypes()
 }
 
-// Next move cursor to next.
+// Next move cursor to next. Attempts to honor context timeout from QueryContext call.
 func (rc *SQLiteRows) Next(dest []driver.Value) error {
 	rc.s.mu.Lock()
 	defer rc.s.mu.Unlock()
+
 	if rc.s.closed {
 		return io.EOF
 	}
+
+	if rc.ctx.Done() == nil {
+		return rc.nextSyncLocked(dest)
+	}
+	resultCh := make(chan error)
+	go func() {
+		resultCh <- rc.nextSyncLocked(dest)
+	}()
+	select {
+	case err := <- resultCh:
+		return err
+	case <-rc.ctx.Done():
+		select {
+		case <-resultCh: // no need to interrupt
+		default:
+			// this is still racy and can be no-op if executed between sqlite3_* calls in nextSyncLocked.
+			C.sqlite3_interrupt(rc.s.c.db)
+			<-resultCh // ensure goroutine completed
+		}
+		return rc.ctx.Err()
+	}
+}
+
+// nextSyncLocked moves cursor to next; must be called with locked mutex.
+func (rc *SQLiteRows) nextSyncLocked(dest []driver.Value) error {
 	rv := C._sqlite3_step_internal(rc.s.s)
 	if rv == C.SQLITE_DONE {
 		return io.EOF