fix: obey main context

runner.go

@@ -37,9 +37,9 @@ type Writer interface {
 	Write(context.Context, []string) error
 }
 
-// Process accepts string slice, does what it should
+// Processor accepts string slice, does what it should
 // and returns output. Non-nil error returned
-// by Processor terminates stops further processing.
+// by Processor stops further processing.
 type Processor func(context.Context, []string) ([]string, error)
 
 type RunConfig struct {
@@ -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
@@ -118,6 +120,7 @@ func Run(ctx context.Context, r RunConfig) error {
 		return nil
 	})
 
+	// run processing routines
 	grp.Go(func() error {
 		// will close write chan once
 		// all workers are done
@@ -136,12 +139,16 @@ func Run(ctx context.Context, r RunConfig) error {
 					}
 
 					wrch <- result
+
+					// if one of workers died or parent context expired
+					// we should die too
+					if err := innrctx.Err(); err != nil {
+						return nil
+					}
 				}
 
 				return nil
-
 			})
-
 		}
 
 		if err := workergrp.Wait(); err != nil {