Removed ensureMainThread() now that the latest Go has a guarantee (which was always true) about the main thread given runtime.LockOSThread() in init().

link_darwin_amd64.go

@@ -3,21 +3,5 @@
 package ui
 
 // #cgo CFLAGS: -mmacosx-version-min=10.8 -DMACOSX_DEPLOYMENT_TARGET=10.8
-// #cgo LDFLAGS: ${SRCDIR}/libui_darwin_amd64.a -framework Foundation -framework AppKit -lpthread -mmacosx-version-min=10.8
-// #include <CoreFoundation/CoreFoundation.h>
-// #include <pthread.h>
-// extern void _CFRunLoopSetCurrent(CFRunLoopRef);
-// extern pthread_t _CFMainPThread;
+// #cgo LDFLAGS: ${SRCDIR}/libui_darwin_amd64.a -framework Foundation -framework AppKit -mmacosx-version-min=10.8
 import "C"
-
-// OS X cares very deeply if we don't run on the very first thread the OS creates
-// why? who knows. it's stupid and completely indefensible. let's use undocumented APIs to get around it.
-// apple uses them too: http://www.opensource.apple.com/source/kext_tools/kext_tools-19.2/kextd_main.c?txt
-// apple HAS SUGGESTED them too: http://lists.apple.com/archives/darwin-development/2002/Sep/msg00250.html
-// gstreamer uses them too: http://cgit.freedesktop.org/gstreamer/gst-plugins-good/tree/sys/osxvideo/osxvideosink.m
-func ensureMainThread() {
-	// TODO set to nil like the apple code?
-	C._CFRunLoopSetCurrent(C.CFRunLoopGetMain())
-	// TODO is this part necessary?
-	C._CFMainPThread = C.pthread_self()
-}

link_linux_386.go

@@ -8,7 +8,3 @@ package ui
 // #cgo LDFLAGS: ${SRCDIR}/libui_linux_386.a -lm -ldl
 // #cgo pkg-config: gtk+-3.0
 import "C"
-
-func ensureMainThread() {
-	// do nothing; GTK+ doesn't care which thread we're on so long as we don't change it after starting
-}

link_linux_amd64.go

@@ -8,7 +8,3 @@ package ui
 // #cgo LDFLAGS: ${SRCDIR}/libui_linux_amd64.a -lm -ldl
 // #cgo pkg-config: gtk+-3.0
 import "C"
-
-func ensureMainThread() {
-	// do nothing; GTK+ doesn't care which thread we're on so long as we don't change it after starting
-}

link_windows_386.go

@@ -6,7 +6,3 @@ package ui
 // /* note the order; also note the lack of uuid */
 // #cgo LDFLAGS: -luser32 -lkernel32 -lusp10 -lgdi32 -lcomctl32 -luxtheme -lmsimg32 -lcomdlg32 -ld2d1 -ldwrite -lole32 -loleaut32 -loleacc -static -static-libgcc -static-libstdc++
 import "C"
-
-func ensureMainThread() {
-	// do nothing; Windows doesn't care which thread we're on so long as we don't change it after starting
-}

link_windows_amd64.go

@@ -6,7 +6,3 @@ package ui
 // /* note the order; also note the lack of uuid */
 // #cgo LDFLAGS: -luser32 -lkernel32 -lusp10 -lgdi32 -lcomctl32 -luxtheme -lmsimg32 -lcomdlg32 -ld2d1 -ldwrite -lole32 -loleaut32 -loleacc -static -static-libgcc -static-libstdc++
 import "C"
-
-func ensureMainThread() {
-	// do nothing; Windows doesn't care which thread we're on so long as we don't change it after starting
-}

main.go

@@ -24,6 +24,13 @@ import (
 // }
 import "C"
 
+// make sure main() runs on the first thread created by the OS
+// if main() calls Main(), things will just work on macOS, where the first thread created by the OS is the only thread allowed to be the main GUI thread
+// we might as well lock the OS thread for the other platforms here too (though on those it doesn't matter *which* thread we lock to)
+func init() {
+	runtime.LockOSThread()
+}
+
 // Main initializes package ui, runs f to set up the program,
 // and executes the GUI main loop. f should set up the program's
 // initial state: open the main window, create controls, and set up
@@ -32,29 +39,19 @@ import "C"
 // nil. If package ui fails to initialize, Main returns an appropriate
 // error.
 func Main(f func()) error {
-	errchan := make(chan error)
-	go start(errchan, f)
-	return <-errchan
-}
-
-func start(errchan chan error, f func()) {
-	runtime.LockOSThread()
-
-	ensureMainThread()
-
 	// TODO HEAP SAFETY
 	opts := C.uiInitOptions{}
 	estr := C.uiInit(&opts)
 	if estr != nil {
-		errchan <- errors.New(C.GoString(estr))
+		err := errors.New(C.GoString(estr))
 		C.uiFreeInitError(estr)
-		return
+		return err
 	}
 	// set up OnShouldQuit()
 	C.realOnShouldQuit()
 	QueueMain(f)
 	C.uiMain()
-	errchan <- nil
+	return nil
 }
 
 // Quit queues a return from Main. It does not exit the program.