From f27db333052aa24a0aad135c09ce7969bf31bc56 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Sun, 19 May 2019 09:50:19 +0000
Subject: [PATCH] worker/types/worker: make ID allocation atomic

Message IDs are allocated for both messages from UI to workers and the other
way around. Hence, the global nextId variable is accessed from multiple
goroutines.

Instead, use atomic to access the global counter.
---
 worker/types/messages.go | 10 +++++-----
 worker/types/worker.go   | 11 ++++++-----
 2 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/worker/types/messages.go b/worker/types/messages.go
index 0cb6eeb..eb54a15 100644
--- a/worker/types/messages.go
+++ b/worker/types/messages.go
@@ -12,13 +12,13 @@ import (
 
 type WorkerMessage interface {
 	InResponseTo() WorkerMessage
-	getId() int
-	setId(id int)
+	getId() int64
+	setId(id int64)
 }
 
 type Message struct {
 	inResponseTo WorkerMessage
-	id           int
+	id           int64
 }
 
 func RespondTo(msg WorkerMessage) Message {
@@ -31,11 +31,11 @@ func (m Message) InResponseTo() WorkerMessage {
 	return m.inResponseTo
 }
 
-func (m Message) getId() int {
+func (m Message) getId() int64 {
 	return m.id
 }
 
-func (m Message) setId(id int) {
+func (m Message) setId(id int64) {
 	m.id = id
 }
 
diff --git a/worker/types/worker.go b/worker/types/worker.go
index 5647ae3..2ca142b 100644
--- a/worker/types/worker.go
+++ b/worker/types/worker.go
@@ -3,9 +3,10 @@ package types
 import (
 	"log"
 	"sync"
+	"sync/atomic"
 )
 
-var nextId int = 1
+var lastId int64 = 1 // access via atomic
 
 type Backend interface {
 	Run()
@@ -17,7 +18,7 @@ type Worker struct {
 	Messages chan WorkerMessage
 	Logger   *log.Logger
 
-	callbacks map[int]func(msg WorkerMessage) // protected by mutex
+	callbacks map[int64]func(msg WorkerMessage) // protected by mutex
 	mutex     sync.Mutex
 }
 
@@ -26,13 +27,13 @@ func NewWorker(logger *log.Logger) *Worker {
 		Actions:   make(chan WorkerMessage, 50),
 		Messages:  make(chan WorkerMessage, 50),
 		Logger:    logger,
-		callbacks: make(map[int]func(msg WorkerMessage)),
+		callbacks: make(map[int64]func(msg WorkerMessage)),
 	}
 }
 
 func (worker *Worker) setId(msg WorkerMessage) {
-	msg.setId(nextId)
-	nextId++
+	id := atomic.AddInt64(&lastId, 1)
+	msg.setId(id)
 }
 
 func (worker *Worker) setCallback(msg WorkerMessage,