fix: workers obey context

runner.go

@@ -51,13 +51,15 @@ type RunConfig struct {
 	Concurrency int
 }
 
-// Run starts concurrency threads (goroutines), reads from provided Reader,
-// executes each Processor in the order they were provide and records result
-// with provided Writer.
-// At first Read is called offset times with output of Read being discarded.
+// Run starts the script described by r.
+// First Read is called offset times with output of Read being discarded.
 // Then limit Reads are made and processor is called for each portion
-// of data. If limit is 0 then Runner keep processing input until it receives
+// of data. If limit is 0 then Run keep processing input until it receives
 // EOF from Reader.
+// Run fails on any error including Reader error, Writer error and Processor error.
+// If an error is encountered the writer operation will be attampted anyway so that
+// the output is left in consistent state, recording what has been actually done
+// by Processor.
 func Run(ctx context.Context, r RunConfig) error {
 	if r.Concurrency == 0 {
 		r.Concurrency = 1