From 9acedd8e4d2cfc01d33a27bf19ee7432d67f867c Mon Sep 17 00:00:00 2001
From: gutmet <me.git@gutmet.org>
Date: Thu, 4 Jul 2019 18:42:21 +0200
Subject: [PATCH] parallelize calls to sendmail

---
 picolist.go | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/picolist.go b/picolist.go
index 800888d..40caf0b 100644
--- a/picolist.go
+++ b/picolist.go
@@ -13,6 +13,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -118,7 +119,7 @@ func recipients(members hashset) ([]bulkRecipients, error) {
 	return splitRecipients(rcpts), nil
 }
 
-func sendmail(original *mail.Message, mail string, returnPath string, recps string) error {
+func sendmail(original *mail.Message, mail string, returnPath string, recps string, errChan chan error, wg *sync.WaitGroup) {
 	if debug {
 		log(original, sendmailPath+" -f "+returnPath+" "+recps+"\n")
 	}
@@ -126,9 +127,9 @@ func sendmail(original *mail.Message, mail string, returnPath string, recps stri
 	cmd.Stdin = strings.NewReader(mail)
 	e := cmd.Run()
 	if e != nil {
-		return err("error on call to sendmail", e)
+		errChan <- err("error on call to sendmail", e)
 	}
-	return nil
+	wg.Done()
 }
 
 func forward(mail *mail.Message, returnPath string, members hashset) []error {
@@ -140,8 +141,17 @@ func forward(mail *mail.Message, returnPath string, members hashset) []error {
 	if len(errs) > 0 {
 		return errs
 	}
+	var wg sync.WaitGroup
+	wg.Add(len(rcpts))
+	errChan := make(chan error)
 	for _, bulk := range rcpts {
-		err = sendmail(mail, flatmail, returnPath, bulk.String())
+		go sendmail(mail, flatmail, returnPath, bulk.String(), errChan, &wg)
+	}
+	go func(errChan chan error, wg *sync.WaitGroup) {
+		wg.Wait()
+		close(errChan)
+	}(errChan, &wg)
+	for err := range errChan {
 		errs = appendErr(errs, err)
 	}
 	return errs