thread: Rename mainthread -> thread and add struct Thread

This enables thread available not only for the main thread but also
any threads.

This is a preparation for iOS Metal, that runs drawing functions on
a particular thread.

Updates #737

internal/driver/graphics.go

@@ -17,9 +17,11 @@ package driver
 import (
 	"github.com/hajimehoshi/ebiten/internal/affine"
 	"github.com/hajimehoshi/ebiten/internal/graphics"
+	"github.com/hajimehoshi/ebiten/internal/thread"
 )
 
 type Graphics interface {
+	SetThread(thread *thread.Thread)
 	Begin()
 	End()
 	SetWindow(window uintptr)

internal/graphicsdriver/metal/driver.go

@@ -26,7 +26,7 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/graphicsdriver/metal/ca"
 	"github.com/hajimehoshi/ebiten/internal/graphicsdriver/metal/mtl"
-	"github.com/hajimehoshi/ebiten/internal/mainthread"
+	"github.com/hajimehoshi/ebiten/internal/thread"
 )
 
 // #cgo CFLAGS: -x objective-c -mmacosx-version-min=10.11
@@ -301,6 +301,8 @@ type Driver struct {
 
 	maxImageSize int
 
+	t *thread.Thread
+
 	pool unsafe.Pointer
 }
 
@@ -310,8 +312,12 @@ func Get() *Driver {
 	return &theDriver
 }
 
+func (d *Driver) SetThread(thread *thread.Thread) {
+	d.t = thread
+}
+
 func (d *Driver) Begin() {
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		// NSAutoreleasePool is required to release drawable correctly (#847).
 		// https://developer.apple.com/library/archive/documentation/3DDrawing/Conceptual/MTLBestPracticesGuide/Drawables.html
 		d.pool = C.allocAutoreleasePool()
@@ -321,7 +327,7 @@ func (d *Driver) Begin() {
 
 func (d *Driver) End() {
 	d.flush(false, true)
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		d.screenDrawable = ca.MetalDrawable{}
 		C.releaseAutoreleasePool(d.pool)
 		d.pool = nil
@@ -330,7 +336,7 @@ func (d *Driver) End() {
 }
 
 func (d *Driver) SetWindow(window uintptr) {
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		// Note that [NSApp mainWindow] returns nil when the window is borderless.
 		// Then the window is needed to be given.
 		d.window = window
@@ -339,7 +345,7 @@ func (d *Driver) SetWindow(window uintptr) {
 }
 
 func (d *Driver) SetVertices(vertices []float32, indices []uint16) {
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		if d.vb != (mtl.Buffer{}) {
 			d.vb.Release()
 		}
@@ -357,7 +363,7 @@ func (d *Driver) Flush() {
 }
 
 func (d *Driver) flush(wait bool, present bool) {
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		if d.cb == (mtl.CommandBuffer{}) {
 			return nil
 		}
@@ -378,7 +384,7 @@ func (d *Driver) flush(wait bool, present bool) {
 
 func (d *Driver) checkSize(width, height int) {
 	m := 0
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		if d.maxImageSize == 0 {
 			d.maxImageSize = 4096
 			// https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf
@@ -438,7 +444,7 @@ func (d *Driver) NewImage(width, height int) (driver.Image, error) {
 		Usage: mtl.TextureUsageShaderRead,
 	}
 	var t mtl.Texture
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		t = d.device.MakeTexture(td)
 		return nil
 	})
@@ -451,7 +457,7 @@ func (d *Driver) NewImage(width, height int) (driver.Image, error) {
 }
 
 func (d *Driver) NewScreenFramebufferImage(width, height int) (driver.Image, error) {
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		d.ml.SetDrawableSize(width, height)
 		return nil
 	})
@@ -464,7 +470,7 @@ func (d *Driver) NewScreenFramebufferImage(width, height int) (driver.Image, err
 }
 
 func (d *Driver) Reset() error {
-	if err := mainthread.Run(func() error {
+	if err := d.t.Run(func() error {
 		if d.cq != (mtl.CommandQueue{}) {
 			d.cq.Release()
 			d.cq = mtl.CommandQueue{}
@@ -606,7 +612,7 @@ func (d *Driver) Reset() error {
 }
 
 func (d *Driver) Draw(indexLen int, indexOffset int, mode graphics.CompositeMode, colorM *affine.ColorM, filter graphics.Filter, address graphics.Address) error {
-	if err := mainthread.Run(func() error {
+	if err := d.t.Run(func() error {
 		// NSView can be changed anytime (probably). Set this everyframe.
 		setView(d.window, d.ml)
 
@@ -690,16 +696,16 @@ func (d *Driver) Draw(indexLen int, indexOffset int, mode graphics.CompositeMode
 }
 
 func (d *Driver) ResetSource() {
-	mainthread.Run(func() error {
+	d.t.Run(func() error {
 		d.src = nil
 		return nil
 	})
 }
 
 func (d *Driver) SetVsyncEnabled(enabled bool) {
-	// TODO: Now SetVsyncEnabled is called only from the main thread, and mainthread.Run is not available since
+	// TODO: Now SetVsyncEnabled is called only from the main thread, and d.t.Run is not available since
 	// recursive function call via Run is forbidden.
-	// Fix this to use mainthread.Run to avoid confusion.
+	// Fix this to use d.t.Run to avoid confusion.
 	d.ml.SetDisplaySyncEnabled(enabled)
 }
 
@@ -732,7 +738,7 @@ func (i *Image) viewportSize() (int, int) {
 }
 
 func (i *Image) Dispose() {
-	mainthread.Run(func() error {
+	i.driver.t.Run(func() error {
 		if i.texture != (mtl.Texture{}) {
 			i.texture.Release()
 			i.texture = mtl.Texture{}
@@ -749,7 +755,7 @@ func (i *Image) IsInvalidated() bool {
 }
 
 func (i *Image) syncTexture() {
-	mainthread.Run(func() error {
+	i.driver.t.Run(func() error {
 		if i.driver.cb != (mtl.CommandBuffer{}) {
 			panic("metal: command buffer must be empty at syncTexture: flush is not called yet?")
 		}
@@ -769,7 +775,7 @@ func (i *Image) Pixels() ([]byte, error) {
 	i.syncTexture()
 
 	b := make([]byte, 4*i.width*i.height)
-	mainthread.Run(func() error {
+	i.driver.t.Run(func() error {
 		i.texture.GetBytes(&b[0], uintptr(4*i.width), mtl.Region{
 			Size: mtl.Size{i.width, i.height, 1},
 		}, 0)
@@ -779,14 +785,14 @@ func (i *Image) Pixels() ([]byte, error) {
 }
 
 func (i *Image) SetAsDestination() {
-	mainthread.Run(func() error {
+	i.driver.t.Run(func() error {
 		i.driver.dst = i
 		return nil
 	})
 }
 
 func (i *Image) SetAsSource() {
-	mainthread.Run(func() error {
+	i.driver.t.Run(func() error {
 		i.driver.src = i
 		return nil
 	})
@@ -795,7 +801,7 @@ func (i *Image) SetAsSource() {
 func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 	i.driver.flush(true, false)
 
-	mainthread.Run(func() error {
+	i.driver.t.Run(func() error {
 		i.texture.ReplaceRegion(mtl.Region{
 			Origin: mtl.Origin{x, y, 0},
 			Size:   mtl.Size{width, height, 1},

internal/graphicsdriver/opengl/context.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 
 	"github.com/hajimehoshi/ebiten/internal/graphics"
+	"github.com/hajimehoshi/ebiten/internal/thread"
 )
 
 func convertOperation(op graphics.Operation) operation {
@@ -48,6 +49,9 @@ type context struct {
 	lastViewportHeight int
 	lastCompositeMode  graphics.CompositeMode
 	maxTextureSize     int
+
+	t *thread.Thread
+
 	contextImpl
 }
 

internal/graphicsdriver/opengl/context_desktop.go

@@ -25,7 +25,6 @@ import (
 
 	"github.com/hajimehoshi/ebiten/internal/graphics"
 	"github.com/hajimehoshi/ebiten/internal/graphicsdriver/opengl/gl"
-	"github.com/hajimehoshi/ebiten/internal/mainthread"
 )
 
 type (
@@ -76,7 +75,7 @@ type contextImpl struct {
 }
 
 func (c *context) reset() error {
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		if c.init {
 			return nil
 		}
@@ -95,12 +94,12 @@ func (c *context) reset() error {
 	c.lastViewportWidth = 0
 	c.lastViewportHeight = 0
 	c.lastCompositeMode = graphics.CompositeModeUnknown
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.Enable(gl.BLEND)
 		return nil
 	})
 	c.blendFunc(graphics.CompositeModeSourceOver)
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		f := int32(0)
 		gl.GetIntegerv(gl.FRAMEBUFFER_BINDING, &f)
 		c.screenFramebuffer = framebufferNative(f)
@@ -110,7 +109,7 @@ func (c *context) reset() error {
 }
 
 func (c *context) blendFunc(mode graphics.CompositeMode) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		if c.lastCompositeMode == mode {
 			return nil
 		}
@@ -124,7 +123,7 @@ func (c *context) blendFunc(mode graphics.CompositeMode) {
 
 func (c *context) newTexture(width, height int) (textureNative, error) {
 	var texture textureNative
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		var t uint32
 		gl.GenTextures(1, &t)
 		// TODO: Use gl.IsTexture
@@ -138,7 +137,7 @@ func (c *context) newTexture(width, height int) (textureNative, error) {
 		return 0, err
 	}
 	c.bindTexture(texture)
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST)
 		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST)
 		gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
@@ -152,7 +151,7 @@ func (c *context) newTexture(width, height int) (textureNative, error) {
 }
 
 func (c *context) bindFramebufferImpl(f framebufferNative) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.BindFramebufferEXT(gl.FRAMEBUFFER, uint32(f))
 		return nil
 	})
@@ -160,12 +159,12 @@ func (c *context) bindFramebufferImpl(f framebufferNative) {
 
 func (c *context) framebufferPixels(f *framebuffer, width, height int) ([]byte, error) {
 	var pixels []byte
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.Flush()
 		return nil
 	})
 	c.bindFramebuffer(f.native)
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		pixels = make([]byte, 4*width*height)
 		gl.ReadPixels(0, 0, int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(pixels))
 		return nil
@@ -176,14 +175,14 @@ func (c *context) framebufferPixels(f *framebuffer, width, height int) ([]byte,
 }
 
 func (c *context) bindTextureImpl(t textureNative) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.BindTexture(gl.TEXTURE_2D, uint32(t))
 		return nil
 	})
 }
 
 func (c *context) deleteTexture(t textureNative) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		tt := uint32(t)
 		if !gl.IsTexture(tt) {
 			return nil
@@ -198,7 +197,7 @@ func (c *context) deleteTexture(t textureNative) {
 
 func (c *context) isTexture(t textureNative) bool {
 	r := false
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		r = gl.IsTexture(uint32(t))
 		return nil
 	})
@@ -207,7 +206,7 @@ func (c *context) isTexture(t textureNative) bool {
 
 func (c *context) texSubImage2D(t textureNative, p []byte, x, y, width, height int) {
 	c.bindTexture(t)
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.TexSubImage2D(gl.TEXTURE_2D, 0, int32(x), int32(y), int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(p))
 		return nil
 	})
@@ -216,7 +215,7 @@ func (c *context) texSubImage2D(t textureNative, p []byte, x, y, width, height i
 func (c *context) newFramebuffer(texture textureNative) (framebufferNative, error) {
 	var framebuffer framebufferNative
 	var f uint32
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		gl.GenFramebuffersEXT(1, &f)
 		// TODO: Use gl.IsFramebuffer
 		if f <= 0 {
@@ -227,7 +226,7 @@ func (c *context) newFramebuffer(texture textureNative) (framebufferNative, erro
 		return 0, err
 	}
 	c.bindFramebuffer(framebufferNative(f))
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		gl.FramebufferTexture2DEXT(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, uint32(texture), 0)
 		s := gl.CheckFramebufferStatusEXT(gl.FRAMEBUFFER)
 		if s != gl.FRAMEBUFFER_COMPLETE {
@@ -248,14 +247,14 @@ func (c *context) newFramebuffer(texture textureNative) (framebufferNative, erro
 }
 
 func (c *context) setViewportImpl(width, height int) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.Viewport(0, 0, int32(width), int32(height))
 		return nil
 	})
 }
 
 func (c *context) deleteFramebuffer(f framebufferNative) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		ff := uint32(f)
 		if !gl.IsFramebufferEXT(ff) {
 			return nil
@@ -272,7 +271,7 @@ func (c *context) deleteFramebuffer(f framebufferNative) {
 
 func (c *context) newShader(shaderType shaderType, source string) (shader, error) {
 	var sh shader
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		s := gl.CreateShader(uint32(shaderType))
 		if s == 0 {
 			return fmt.Errorf("opengl: glCreateShader failed: shader type: %d", shaderType)
@@ -302,7 +301,7 @@ func (c *context) newShader(shaderType shaderType, source string) (shader, error
 }
 
 func (c *context) deleteShader(s shader) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.DeleteShader(uint32(s))
 		return nil
 	})
@@ -310,7 +309,7 @@ func (c *context) deleteShader(s shader) {
 
 func (c *context) newProgram(shaders []shader, attributes []string) (program, error) {
 	var pr program
-	if err := mainthread.Run(func() error {
+	if err := c.t.Run(func() error {
 		p := gl.CreateProgram()
 		if p == 0 {
 			return errors.New("opengl: glCreateProgram failed")
@@ -341,14 +340,14 @@ func (c *context) newProgram(shaders []shader, attributes []string) (program, er
 }
 
 func (c *context) useProgram(p program) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.UseProgram(uint32(p))
 		return nil
 	})
 }
 
 func (c *context) deleteProgram(p program) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		if !gl.IsProgram(uint32(p)) {
 			return nil
 		}
@@ -368,7 +367,7 @@ func (c *context) getUniformLocationImpl(p program, location string) uniformLoca
 }
 
 func (c *context) uniformInt(p program, location string, v int) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		l := int32(c.locationCache.GetUniformLocation(c, p, location))
 		gl.Uniform1i(l, int32(v))
 		return nil
@@ -376,7 +375,7 @@ func (c *context) uniformInt(p program, location string, v int) {
 }
 
 func (c *context) uniformFloat(p program, location string, v float32) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		l := int32(c.locationCache.GetUniformLocation(c, p, location))
 		gl.Uniform1f(l, v)
 		return nil
@@ -384,7 +383,7 @@ func (c *context) uniformFloat(p program, location string, v float32) {
 }
 
 func (c *context) uniformFloats(p program, location string, v []float32) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		l := int32(c.locationCache.GetUniformLocation(c, p, location))
 		switch len(v) {
 		case 2:
@@ -401,21 +400,21 @@ func (c *context) uniformFloats(p program, location string, v []float32) {
 }
 
 func (c *context) vertexAttribPointer(p program, index int, size int, dataType dataType, stride int, offset int) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.VertexAttribPointer(uint32(index), int32(size), uint32(dataType), false, int32(stride), gl.PtrOffset(offset))
 		return nil
 	})
 }
 
 func (c *context) enableVertexAttribArray(p program, index int) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.EnableVertexAttribArray(uint32(index))
 		return nil
 	})
 }
 
 func (c *context) disableVertexAttribArray(p program, index int) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.DisableVertexAttribArray(uint32(index))
 		return nil
 	})
@@ -423,7 +422,7 @@ func (c *context) disableVertexAttribArray(p program, index int) {
 
 func (c *context) newArrayBuffer(size int) buffer {
 	var bf buffer
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		var b uint32
 		gl.GenBuffers(1, &b)
 		gl.BindBuffer(uint32(arrayBuffer), b)
@@ -436,7 +435,7 @@ func (c *context) newArrayBuffer(size int) buffer {
 
 func (c *context) newElementArrayBuffer(size int) buffer {
 	var bf buffer
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		var b uint32
 		gl.GenBuffers(1, &b)
 		gl.BindBuffer(uint32(elementArrayBuffer), b)
@@ -448,28 +447,28 @@ func (c *context) newElementArrayBuffer(size int) buffer {
 }
 
 func (c *context) bindBuffer(bufferType bufferType, b buffer) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.BindBuffer(uint32(bufferType), uint32(b))
 		return nil
 	})
 }
 
 func (c *context) arrayBufferSubData(data []float32) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.BufferSubData(uint32(arrayBuffer), 0, len(data)*4, gl.Ptr(data))
 		return nil
 	})
 }
 
 func (c *context) elementArrayBufferSubData(data []uint16) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.BufferSubData(uint32(elementArrayBuffer), 0, len(data)*2, gl.Ptr(data))
 		return nil
 	})
 }
 
 func (c *context) deleteBuffer(b buffer) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		bb := uint32(b)
 		gl.DeleteBuffers(1, &bb)
 		return nil
@@ -477,7 +476,7 @@ func (c *context) deleteBuffer(b buffer) {
 }
 
 func (c *context) drawElements(len int, offsetInBytes int) {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.DrawElements(gl.TRIANGLES, int32(len), gl.UNSIGNED_SHORT, gl.PtrOffset(offsetInBytes))
 		return nil
 	})
@@ -485,7 +484,7 @@ func (c *context) drawElements(len int, offsetInBytes int) {
 
 func (c *context) maxTextureSizeImpl() int {
 	size := 0
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		s := int32(0)
 		gl.GetIntegerv(gl.MAX_TEXTURE_SIZE, &s)
 		size = int(s)
@@ -495,7 +494,7 @@ func (c *context) maxTextureSizeImpl() int {
 }
 
 func (c *context) flush() {
-	_ = mainthread.Run(func() error {
+	_ = c.t.Run(func() error {
 		gl.Flush()
 		return nil
 	})

internal/graphicsdriver/opengl/driver.go

@@ -20,6 +20,7 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/affine"
 	"github.com/hajimehoshi/ebiten/internal/driver"
 	"github.com/hajimehoshi/ebiten/internal/graphics"
+	"github.com/hajimehoshi/ebiten/internal/thread"
 )
 
 var theDriver Driver
@@ -33,6 +34,10 @@ type Driver struct {
 	context context
 }
 
+func (d *Driver) SetThread(thread *thread.Thread) {
+	d.context.t = thread
+}
+
 func (d *Driver) Begin() {
 	// Do nothing.
 }

internal/thread/thread.go

@@ -12,30 +12,35 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package mainthread
+package thread
 
 import (
-	"runtime"
 	"sync/atomic"
 )
 
-func init() {
+// Thread represents an OS thread.
-	runtime.LockOSThread()
+type Thread struct {
+	started int32
+	funcs   chan func()
 }
 
-var (
+// New creates a new thread.
-	started = int32(0)
-	funcs   = make(chan func())
-)
-
-// Loop starts the main-thread loop.
 //
-// Loop must be called on the main thread.
+// It is assumed that the OS thread is fixed by runtime.LockOSThread when New is called.
-func Loop(ch <-chan error) error {
+func New() *Thread {
-	atomic.StoreInt32(&started, 1)
+	return &Thread{
+		funcs: make(chan func()),
+	}
+}
+
+// Loop starts the thread loop.
+//
+// Loop must be called on the thread.
+func (t *Thread) Loop(ch <-chan error) error {
+	atomic.StoreInt32(&t.started, 1)
 	for {
 		select {
-		case f := <-funcs:
+		case f := <-t.funcs:
 			f()
 		case err := <-ch:
 			// ch returns a value not only when an error occur but also it is closed.
@@ -44,18 +49,17 @@ func Loop(ch <-chan error) error {
 	}
 }
 
-// Run calls f on the main thread.
+// Run calls f on the thread.
 //
-// Do not call this from the main thread. This would block forever.
+// Do not call this from the same thread. This would block forever.
-func Run(f func() error) error {
+func (t *Thread) Run(f func() error) error {
-	if atomic.LoadInt32(&started) == 0 {
+	if atomic.LoadInt32(&t.started) == 0 {
-		// TODO: This can reach from other goroutine before Loop is called (#809).
+		panic("thread: the thread loop is not started yet")
-		// panic("mainthread: the mainthread loop is not started yet")
 	}
 
 	ch := make(chan struct{})
 	var err error
-	funcs <- func() {
+	t.funcs <- func() {
 		err = f()
 		close(ch)
 	}

internal/uidriver/glfw/ui.go

@@ -29,7 +29,7 @@ import (
 	"github.com/hajimehoshi/ebiten/internal/devicescale"
 	"github.com/hajimehoshi/ebiten/internal/driver"
 	"github.com/hajimehoshi/ebiten/internal/glfw"
-	"github.com/hajimehoshi/ebiten/internal/mainthread"
+	"github.com/hajimehoshi/ebiten/internal/thread"
 )
 
 type UserInterface struct {
@@ -66,6 +66,7 @@ type UserInterface struct {
 	graphics driver.Graphics
 	input    Input
 
+	t *thread.Thread
 	m sync.Mutex
 }
 
@@ -172,7 +173,7 @@ func getCachedMonitor(wx, wy int) (*cachedMonitor, bool) {
 
 func (u *UserInterface) mainThreadLoop(ch <-chan error) error {
 	u.setRunning(true)
-	if err := mainthread.Loop(ch); err != nil {
+	if err := u.t.Loop(ch); err != nil {
 		return err
 	}
 	u.setRunning(false)
@@ -277,7 +278,7 @@ func (u *UserInterface) ScreenSizeInFullscreen() (int, int) {
 
 	var v *glfw.VidMode
 	s := 0.0
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		v = u.currentMonitor().GetVideoMode()
 		s = u.glfwScale()
 		return nil
@@ -289,7 +290,7 @@ func (u *UserInterface) SetScreenSize(width, height int) {
 	if !u.isRunning() {
 		panic("ui: Run is not called yet")
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		// TODO: What if the window is maximized? (#320)
 		u.setScreenSize(width, height, u.scale, u.isFullscreen(), u.vsync)
 		return nil
@@ -300,7 +301,7 @@ func (u *UserInterface) SetScreenScale(scale float64) {
 	if !u.isRunning() {
 		panic("ui: Run is not called yet")
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		// TODO: What if the window is maximized? (#320)
 		u.setScreenSize(u.width, u.height, scale, u.isFullscreen(), u.vsync)
 		return nil
@@ -312,7 +313,7 @@ func (u *UserInterface) ScreenScale() float64 {
 		return 0
 	}
 	s := 0.0
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		s = u.scale
 		return nil
 	})
@@ -332,7 +333,7 @@ func (u *UserInterface) IsFullscreen() bool {
 		return u.isInitFullscreen()
 	}
 	b := false
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		b = u.isFullscreen()
 		return nil
 	})
@@ -344,7 +345,7 @@ func (u *UserInterface) SetFullscreen(fullscreen bool) {
 		u.setInitFullscreen(fullscreen)
 		return
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		u.setScreenSize(u.width, u.height, u.scale, fullscreen, u.vsync)
 		return nil
 	})
@@ -369,7 +370,7 @@ func (u *UserInterface) SetVsyncEnabled(enabled bool) {
 		u.m.Unlock()
 		return
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		u.setScreenSize(u.width, u.height, u.scale, u.isFullscreen(), enabled)
 		return nil
 	})
@@ -386,7 +387,7 @@ func (u *UserInterface) SetWindowTitle(title string) {
 	if !u.isRunning() {
 		return
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		u.window.SetTitle(title)
 		return nil
 	})
@@ -397,7 +398,7 @@ func (u *UserInterface) SetWindowIcon(iconImages []image.Image) {
 		u.setInitIconImages(iconImages)
 		return
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		u.window.SetIcon(iconImages)
 		return nil
 	})
@@ -413,7 +414,7 @@ func (u *UserInterface) ScreenPadding() (x0, y0, x1, y1 float64) {
 		}
 		// The window width can be bigger than the game screen width (#444).
 		ox := 0.0
-		_ = mainthread.Run(func() error {
+		_ = u.t.Run(func() error {
 			ox = (float64(u.windowWidth)*u.actualScreenScale() - float64(u.width)*u.actualScreenScale()) / 2
 			return nil
 		})
@@ -426,7 +427,7 @@ func (u *UserInterface) ScreenPadding() (x0, y0, x1, y1 float64) {
 	gs := 0.0
 	vw := 0.0
 	vh := 0.0
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		m := u.window.GetMonitor()
 		d = devicescale.GetAt(m.GetPos())
 		sx = float64(u.width) * u.actualScreenScale()
@@ -451,7 +452,7 @@ func (u *UserInterface) adjustPosition(x, y int) (int, int) {
 	}
 	ox, oy, _, _ := u.ScreenPadding()
 	s := 0.0
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		s = u.actualScreenScale()
 		return nil
 	})
@@ -463,7 +464,7 @@ func (u *UserInterface) IsCursorVisible() bool {
 		return u.isInitCursorVisible()
 	}
 	v := false
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		v = u.window.GetInputMode(glfw.CursorMode) == glfw.CursorNormal
 		return nil
 	})
@@ -475,7 +476,7 @@ func (u *UserInterface) SetCursorVisible(visible bool) {
 		u.setInitCursorVisible(visible)
 		return
 	}
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		c := glfw.CursorNormal
 		if !visible {
 			c = glfw.CursorHidden
@@ -490,7 +491,7 @@ func (u *UserInterface) IsWindowDecorated() bool {
 		return u.isInitWindowDecorated()
 	}
 	v := false
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		v = u.window.GetAttrib(glfw.Decorated) == glfw.True
 		return nil
 	})
@@ -508,7 +509,7 @@ func (u *UserInterface) SetWindowDecorated(decorated bool) {
 	// TODO: Now SetAttrib doesn't exist on GLFW 3.2. Revisit later (#556).
 	// If SetAttrib exists, the implementation would be:
 	//
-	//     _ = mainthread.Run(func() error {
+	//     _ = u.t.Run(func() error {
 	//         v := glfw.False
 	//         if decorated {
 	//             v = glfw.True
@@ -523,7 +524,7 @@ func (u *UserInterface) IsWindowResizable() bool {
 		return u.isInitWindowResizable()
 	}
 	v := false
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		v = u.window.GetAttrib(glfw.Resizable) == glfw.True
 		return nil
 	})
@@ -547,7 +548,7 @@ func (u *UserInterface) DeviceScaleFactor() float64 {
 		return devicescale.GetAt(u.initMonitor.GetPos())
 	}
 
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		m := u.currentMonitor()
 		f = devicescale.GetAt(m.GetPos())
 		return nil
@@ -555,7 +556,15 @@ func (u *UserInterface) DeviceScaleFactor() float64 {
 	return f
 }
 
+func init() {
+	// Lock the main thread.
+	runtime.LockOSThread()
+}
+
 func (u *UserInterface) Run(width, height int, scale float64, title string, context driver.UIContext, graphics driver.Graphics) error {
+	// Initialize the main thread first so the thread is available at u.run (#809).
+	u.t = thread.New()
+
 	ch := make(chan error)
 	go func() {
 		defer close(ch)
@@ -575,8 +584,9 @@ func (u *UserInterface) RunWithoutMainLoop(width, height int, scale float64, tit
 }
 
 func (u *UserInterface) run(width, height int, scale float64, title string, context driver.UIContext, graphics driver.Graphics) error {
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		u.graphics = graphics
+		u.graphics.SetThread(u.t)
 
 		if graphics.IsGL() {
 			glfw.WindowHint(glfw.ContextVersionMajor, 2)
@@ -676,7 +686,7 @@ func (u *UserInterface) run(width, height int, scale float64, title string, cont
 	})
 
 	var w uintptr
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		w = u.nativeWindow()
 		return nil
 	})
@@ -722,7 +732,7 @@ func (u *UserInterface) updateSize(context driver.UIContext) {
 	actualScale := 0.0
 	sizeChanged := false
 	// TODO: Is it possible to reduce 'runOnMainThread' calls?
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		actualScale = u.actualScreenScale()
 		if u.lastActualScale != actualScale {
 			u.forceSetScreenSize(u.width, u.height, u.scale, u.isFullscreen(), u.vsync)
@@ -744,7 +754,7 @@ func (u *UserInterface) updateSize(context driver.UIContext) {
 
 func (u *UserInterface) update(context driver.UIContext) error {
 	shouldClose := false
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		shouldClose = u.window.ShouldClose()
 		return nil
 	})
@@ -752,7 +762,7 @@ func (u *UserInterface) update(context driver.UIContext) error {
 		return driver.RegularTermination
 	}
 
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		if u.isInitFullscreen() {
 			u.setScreenSize(u.width, u.height, u.scale, true, u.vsync)
 			u.setInitFullscreen(false)
@@ -763,7 +773,7 @@ func (u *UserInterface) update(context driver.UIContext) error {
 	// This call is needed for initialization.
 	u.updateSize(context)
 
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		glfw.PollEvents()
 
 		u.input.update(u.window, u.getScale()*u.glfwScale())
@@ -789,7 +799,7 @@ func (u *UserInterface) update(context driver.UIContext) error {
 	}
 
 	// Update the screen size when the window is resizable.
-	_ = mainthread.Run(func() error {
+	_ = u.t.Run(func() error {
 		w, h := u.reqWidth, u.reqHeight
 		if w != 0 || h != 0 {
 			u.setScreenSize(w, h, u.scale, u.isFullscreen(), u.vsync)
@@ -803,7 +813,7 @@ func (u *UserInterface) update(context driver.UIContext) error {
 
 func (u *UserInterface) loop(context driver.UIContext) error {
 	defer func() {
-		_ = mainthread.Run(func() error {
+		_ = u.t.Run(func() error {
 			glfw.Terminate()
 			return nil
 		})
@@ -817,7 +827,7 @@ func (u *UserInterface) loop(context driver.UIContext) error {
 		vsync := u.vsync
 		u.m.Unlock()
 
-		_ = mainthread.Run(func() error {
+		_ = u.t.Run(func() error {
 			if !vsync {
 				u.swapBuffers()
 				return nil