thread: Use an error value instead of context.Context

internal/thread/thread.go

@@ -15,7 +15,7 @@
 package thread
 
 import (
-	"context"
+	"errors"
 )
 
 // Thread represents an OS thread.
@@ -34,20 +34,20 @@ func New() *Thread {
 	}
 }
 
-// Loop starts the thread loop.
+// BreakLoop represents an termination of the loop.
+var BreakLoop = errors.New("break loop")
+
+// Loop starts the thread loop until a posted function returns BreakLoop.
 //
 // Loop must be called on the thread.
-//
-// Loop can be called multiple times.
-func (t *Thread) Loop(context context.Context) {
-loop:
-	for {
-		select {
-		case f := <-t.funcs:
-			t.results <- f()
-		case <-context.Done():
-			break loop
+func (t *Thread) Loop() {
+	for f := range t.funcs {
+		err := f()
+		if err == BreakLoop {
+			t.results <- nil
+			return
 		}
+		t.results <- err
 	}
 }
 
@@ -55,6 +55,8 @@ loop:
 //
 // Do not call this from the same thread. This would block forever.
 //
+// If f returns BreakLoop, Loop returns.
+//
 // Call blocks if Loop is not called.
 func (t *Thread) Call(f func() error) error {
 	t.funcs <- f

internal/uidriver/glfw/ui.go

@@ -20,7 +20,6 @@
 package glfw
 
 import (
-	"context"
 	"fmt"
 	"image"
 	"os"
@@ -602,14 +601,11 @@ func (u *UserInterface) Run(uicontext driver.UIContext) error {
 	u.t = thread.New()
 	u.Graphics().SetThread(u.t)
 
-	ctx, cancel := context.WithCancel(context.Background())
-
 	ch := make(chan error, 1)
 	go func() {
 		defer func() {
 			_ = u.t.Call(func() error {
-				cancel()
-				return nil
+				return thread.BreakLoop
 			})
 		}()
 
@@ -620,7 +616,7 @@ func (u *UserInterface) Run(uicontext driver.UIContext) error {
 	}()
 
 	u.setRunning(true)
-	u.t.Loop(ctx)
+	u.t.Loop()
 	u.setRunning(false)
 	return <-ch
 }

internal/uidriver/mobile/ui.go

@@ -84,24 +84,17 @@ func (u *UserInterface) Update() error {
 	}
 
 	renderCh <- struct{}{}
-	ctx, cancel := context.WithCancel(context.Background())
-	go func() {
-		<-renderEndCh
-		if u.t != nil {
-			// If there is a (main) thread, ensure that cancel is called after every other task is done.
-			u.t.Call(func() error {
-				cancel()
-				return nil
-			})
-		} else {
-			cancel()
-		}
-	}()
-
 	if u.Graphics().IsGL() {
 		if u.glWorker == nil {
 			panic("mobile: glWorker must be initialized but not")
 		}
+
+		ctx, cancel := context.WithCancel(context.Background())
+		go func() {
+			<-renderEndCh
+			cancel()
+		}()
+
 		workAvailable := u.glWorker.WorkAvailable()
 	loop:
 		for {
@@ -118,9 +111,15 @@ func (u *UserInterface) Update() error {
 			}
 		}
 		return nil
-	} else {
-		u.t.Loop(ctx)
 	}
+
+	go func() {
+		<-renderEndCh
+		u.t.Call(func() error {
+			return thread.BreakLoop
+		})
+	}()
+	u.t.Loop()
 	return nil
 }