Major code restructure to allow Cocoa to work correctly. Cocoa requires that the application loop run on the very first OS thread created, not just an any ordinary thread. To support this, your code must now be run by the UI init code. Windows and Unix builds still work fine; Mac OS X fails for reasons I now have to debug.

init.go

@@ -1,20 +1,11 @@
 // 11 february 2014
 package ui
 
-import (
-	"os"
-)
-
-func init() {
-	initDone := make(chan error)
-	go ui(initDone)
-	err := <-initDone
-	if err != nil {
-		// TODO provide copying instructions? will need to be system-specific
-		MsgBoxError("UI Library Init Failure",
-			"A failure occured during UI library initialization:\n%v\n" +
-			"Please report this to the application developer or on http://github.com/andlabs/ui.",
-			err)
-		os.Exit(1)
-	}
+// Go sets up the UI environment and runs main in a goroutine.
+// If initialization fails, Go returns an error.
+// Otherwise, Go does not return to its caller until (unless? TODO) the application loop exits, at which point it returns nil.
+//
+// This model is undesirable, but Cocoa limitations require it.
+func Go(main func()) error {
+	return ui(main)
 }

test.sh

@@ -0,0 +1,2 @@
+cd test
+go build main.go

test/main.go

@@ -1,9 +1,9 @@
 // 11 february 2014
-package ui
+package main
 
 import (
 	"fmt"
-	"testing"
+	. ".."
 )
 
 func gridWindow() (*Window, error) {
@@ -25,7 +25,7 @@ func gridWindow() (*Window, error) {
 	return w, w.Open(g)
 }
 
-func TestMain(t *testing.T) {
+func myMain() {
 	w := NewWindow("Main Window", 320, 240)
 	w.Closing = Event()
 	b := NewButton("Click Me")
@@ -119,3 +119,10 @@ mainloop:
 	gw.Hide()
 	w.Hide()
 }
+
+func main() {
+	err := Go(myMain)
+	if err != nil {
+		panic(err)
+	}
+}

uitask_darwin.go

@@ -17,7 +17,6 @@ We will create an Objective-C class goAppDelegate. It contains two methods:
 
 // #cgo LDFLAGS: -lobjc -framework Foundation -framework AppKit
 // #include "objc_darwin.h"
-// extern void appDelegate_applicationDidFinishLaunching(id, SEL, id);
 // extern void appDelegate_uitask(id, SEL, id);
 import "C"
 
@@ -27,8 +26,6 @@ func msgBoxError(string, string){}
 
 var uitask chan func()
 
-var mtret chan interface{}
-
 var (
 	_NSAutoreleasePool = objc_getClass("NSAutoreleasePool")
 	_NSValue = objc_getClass("NSValue")
@@ -38,36 +35,44 @@ var (
 	_performSelectorOnMainThread =
 		sel_getUid("performSelectorOnMainThread:withObject:waitUntilDone:")
 	_pointerValue = sel_getUid("pointerValue")
+	_run = sel_getUid("run")
 )
 
-func ui(initDone chan error) {
+func ui(main func()) error {
 	runtime.LockOSThread()
 
 	uitask = make(chan func())
-	mtret = make(chan interface{})
-	go mainThread()
-	v := <-mtret
-	if err, ok := v.(error); ok {
-		initDone <- fmt.Errorf("error initializing Cocoa: %v", err)
-		return
-	}
-	appDelegate := v.(C.id)
 
-	for f := range uitask {
-		// we need to make an NSAutoreleasePool, otherwise we get leak warnings on stderr
-		pool := objc_new(_NSAutoreleasePool)
-		fp := C.objc_msgSend_ptr(_NSValue, _valueWithPointer,
-			unsafe.Pointer(&f))
-		C.objc_msgSend_sel_id_bool(
-			appDelegate,
-			_performSelectorOnMainThread,
-			_uitask,
-			fp,
-			C.BOOL(C.YES))			// wait so we can properly drain the autorelease pool; on other platforms we wind up waiting anyway (since the main thread can only handle one thing at a time) so
-		objc_release(pool)
+	NSApp, appDelegate, err := initCocoa()
+	if err != nil {
+		return err
 	}
+
+	// Cocoa must run on the first thread created by the program, so we run our dispatcher on another thread instead
+	go func() {
+		for f := range uitask {
+			// we need to make an NSAutoreleasePool, otherwise we get leak warnings on stderr
+			pool := objc_new(_NSAutoreleasePool)
+			fp := C.objc_msgSend_ptr(_NSValue, _valueWithPointer,
+				unsafe.Pointer(&f))
+			C.objc_msgSend_sel_id_bool(
+				appDelegate,
+				_performSelectorOnMainThread,
+				_uitask,
+				fp,
+				C.BOOL(C.YES))			// wait so we can properly drain the autorelease pool; on other platforms we wind up waiting anyway (since the main thread can only handle one thing at a time) so
+			objc_release(pool)
+		}
+	}()
+
+	go main()
+
+	C.objc_msgSend_noargs(NSApp, _run)
+	return nil
 }
 
+// TODO move to init_darwin.go?
+
 const (
 	_goAppDelegate = "goAppDelegate"
 )
@@ -76,41 +81,22 @@ var (
 	_NSApplication = objc_getClass("NSApplication")
 
 	_sharedApplication = sel_getUid("sharedApplication")
-	_applicationDidFinishLaunching = sel_getUid("applicationDidFinishLaunching:")
-	_run = sel_getUid("run")
 )
 
-func mainThread() {
-	runtime.LockOSThread()
+func initCocoa() (NSApp C.id, appDelegate C.id, err error) {
+	var appdelegateclass C.Class
 
-	_NSApp := C.objc_msgSend_noargs(_NSApplication, _sharedApplication)
-	appdelegateclass, err := makeDelegateClass(_goAppDelegate)
-	if err != nil {
-		mtret <- fmt.Errorf("error creating NSApplication delegate: %v", err)
-		return
-	}
-	err = addDelegateMethod(appdelegateclass, _applicationDidFinishLaunching,
-		C.appDelegate_applicationDidFinishLaunching)
-	if err != nil {
-		mtret <- fmt.Errorf("error adding NSApplication delegate applicationDidFinishLaunching: method (to start UI loop): %v", err)
-		return
-	}
+	NSApp = C.objc_msgSend_noargs(_NSApplication, _sharedApplication)
 	err = addDelegateMethod(appdelegateclass, _uitask, C.appDelegate_uitask)
 	if err != nil {
-		mtret <- fmt.Errorf("error adding NSApplication delegate uitask: method (to do UI tasks): %v", err)
+		err = fmt.Errorf("error adding NSApplication delegate uitask: method (to do UI tasks): %v", err)
 		return
 	}
 	// TODO using objc_new() causes a segfault; find out why
 	// TODO make alloc followed by init (I thought NSObject provided its own init?)
-	appDelegate := objc_alloc(objc_getClass(_goAppDelegate))
-	objc_setDelegate(_NSApp, appDelegate)
-	// and that's it, really
-	C.objc_msgSend_noargs(_NSApp, _run)
-}
+	appDelegate = objc_alloc(objc_getClass(_goAppDelegate))
 
-//export appDelegate_applicationDidFinishLaunching
-func appDelegate_applicationDidFinishLaunching(self C.id, sel C.SEL, arg C.id) {
-	mtret <- self
+	return
 }
 
 //export appDelegate_uitask

uitask_unix.go

@@ -10,15 +10,13 @@ import (
 
 var uitask chan func()
 
-func ui(initDone chan error) {
+func ui(main func()) error {
 	runtime.LockOSThread()
 
 	uitask = make(chan func())
 	if gtk_init() != true {
-		initDone <- fmt.Errorf("gtk_init failed (reason unknown; TODO)")
-		return
+		return fmt.Errorf("gtk_init failed (reason unknown; TODO)")
 	}
-	initDone <- nil
 
 	// thanks to tristan in irc.gimp.net/#gtk
 	gdk_threads_add_idle(func() bool {
@@ -29,5 +27,9 @@ func ui(initDone chan error) {
 		}
 		return true	// don't destroy the callback
 	})
+
+	go main()
+
 	gtk_main()
+	return nil
 }

uitask_windows.go

@@ -35,17 +35,22 @@ var (
 	_postThreadMessage = user32.NewProc("PostThreadMessageW")
 )
 
-func ui(initDone chan error) {
+func ui(main func()) error {
 	runtime.LockOSThread()
 
 	uitask = make(chan *uimsg)
-	initDone <- doWindowsInit()
+	err := doWindowsInit()
+	if err != nil {
+		return err
+	}
 
 	threadIDReq := make(chan uintptr)
 	msglooperrs := make(chan error)
 	go msgloop(threadIDReq, msglooperrs)
 	threadID := <-threadIDReq
 
+	go main()
+
 	quit := false
 	for !quit {
 		select {
@@ -66,6 +71,8 @@ func ui(initDone chan error) {
 			}
 		}
 	}
+
+	return nil
 }
 
 var (