content: add mainthread-naive implementation

content/assets/zero-alloc-call-sched/mainthread-naive/bench-2021-01-25-16:13:23.txt

@@ -0,0 +1,25 @@
+goos: darwin
+goarch: arm64
+pkg: x/mainthread
+BenchmarkDirectCall-8       	1000000000	         0.9441 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9443 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9459 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9563 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9526 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9475 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9495 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9544 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9490 ns/op	       0 B/op	       0 allocs/op
+BenchmarkDirectCall-8       	1000000000	         0.9644 ns/op	       0 B/op	       0 allocs/op
+BenchmarkMainThreadCall-8   	 2673351	       447.7 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2675954	       446.5 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2675186	       448.6 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2681828	       447.4 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2674504	       447.1 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2597884	       457.2 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2670514	       446.2 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2676504	       449.6 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2672632	       449.1 ns/op	     120 B/op	       2 allocs/op
+BenchmarkMainThreadCall-8   	 2668776	       448.3 ns/op	     120 B/op	       2 allocs/op
+PASS
+ok  	x/mainthread	27.356s

content/assets/zero-alloc-call-sched/mainthread-naive/mainthread.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2021 The golang.design Initiative Authors.
+// All rights reserved.
+//
+// The code below is produced by Changkun Ou <[email protected]>.
+
+package mainthread
+
+import (
+	"runtime"
+)
+
+func init() {
+	runtime.LockOSThread()
+}
+
+var funcQ = make(chan func(), runtime.GOMAXPROCS(0))
+
+// Init initializes the functionality of running arbitrary subsequent
+// functions be called on the main system thread.
+//
+// Init must be called in the main.main function.
+func Init(main func()) {
+	done := make(chan struct{})
+	go func() {
+		main()
+		done <- struct{}{}
+	}()
+
+	for {
+		select {
+		case f := <-funcQ:
+			f()
+		case <-done:
+			return
+		}
+	}
+}
+
+// Call calls f on the main thread and blocks until f finishes.
+func Call(f func()) {
+	done := make(chan struct{})
+	funcQ <- func() {
+		f()
+		done <- struct{}{}
+	}
+	<-done
+}

content/assets/zero-alloc-call-sched/mainthread-naive/mainthread_test.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2021 The golang.design Initiative Authors.
+// All rights reserved.
+//
+// The code below is produced by Changkun Ou <[email protected]>.
+
+package mainthread_test
+
+import (
+	"testing"
+	mainthread "x/mainthread-naive"
+)
+
+var f = func() {}
+
+func BenchmarkDirectCall(b *testing.B) {
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		f()
+	}
+}
+
+func BenchmarkMainThreadCall(b *testing.B) {
+	mainthread.Init(func() {
+		b.ReportAllocs()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			mainthread.Call(f)
+		}
+	})
+}