Keep Linux WebViews on one persistent GTK UI thread

internal/webview/goprovider/mainthread_linux.go

@@ -0,0 +1,47 @@
+//go:build linux && cgo
+
+package goprovider
+
+/*
+#cgo pkg-config: gtk+-3.0
+#include <gtk/gtk.h>
+static void pumpGTK(void) {
+  // Bound each batch so Go creation/removal requests cannot be starved.
+  for (int i = 0; i < 64 && g_main_context_pending(NULL); ++i)
+    g_main_context_iteration(NULL, FALSE);
+}
+*/
+import "C"
+
+import (
+	"runtime"
+	"sync"
+	"time"
+)
+
+var gtkThreadOnce sync.Once
+var gtkThreadTasks = make(chan func())
+
+func RunMainThreadLoop(run func() int) int { return run() }
+
+func postMainThreadTask(task func()) bool {
+	gtkThreadOnce.Do(func() {
+		go func() {
+			runtime.LockOSThread()
+			// WebKit must always use its original UI thread, including after
+			// the last page closes. A page cannot stop this shared event loop.
+			ticker := time.NewTicker(10 * time.Millisecond)
+			defer ticker.Stop()
+			for {
+				select {
+				case task := <-gtkThreadTasks:
+					task()
+				case <-ticker.C:
+				}
+				C.pumpGTK()
+			}
+		}()
+	})
+	gtkThreadTasks <- task
+	return true
+}