all: initial implementation

Author: changkun

.github/workflows/mainthread.yml

@@ -0,0 +1,35 @@
+name: mainthread
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: Set up Go 1.x
+      uses: actions/setup-go@v2
+      with:
+        go-version: ^1.13
+      id: go
+
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v2
+
+    - name: Get dependencies
+      run: |
+        go get -v -t -d ./...
+    - name: Test
+      run: |
+        go test -v -coverprofile=coverage.txt -covermode=atomic ./...
+    - name: Upload coverage profile
+      uses: codecov/codecov-action@v1
+      with:
+        token: ${{secrets.CODECOV_TOKEN}}
+        file: coverage.txt

README.md

@@ -1,2 +1,38 @@
 # mainthread
-scheduling events on main thread in Go
+
+[![PkgGoDev](https://pkg.go.dev/badge/golang.design/x/mainthread)](https://pkg.go.dev/golang.design/x/mainthread) [![Go Report Card](https://goreportcard.com/badge/golang.design/x/mainthread)](https://goreportcard.com/report/golang.design/x/mainthread)
+![mainthread](https://github.com/golang-design/mainthread/workflows/mainthread/badge.svg?branch=master)
+
+Package mainthread schedules function calls on the main thread in Go.
+
+```
+import "golang.design/x/mainthread"
+```
+
+## Quick Start
+
+```go
+package main
+
+import "golang.design/x/mainthread"
+
+func main() {
+    mainthread.Init(func() {
+        mainthread.Call(func() {
+            // ... runs on the main thread ...
+        })
+
+        go func() {
+            // ... runs concurrently ...
+        }()
+
+        mainthread.Call(func() {
+            // ... runs on the main thread ...
+        })
+    })
+}
+```
+
+## License
+
+GNU GPLv3 © 2020 The golang.design Initiative Authors

go.mod

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+module golang.design/x/mainthread
+
+go 1.15

mainthread.go

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+// Copyright 2020 The golang.design Initiative Authors.
+// All rights reserved. Use of this source code is governed
+// by a GNU GPLv3 license that can be found in the LICENSE file.
+
+package mainthread // import "golang.design/x/mainthread"
+
+import "runtime"
+
+// FIXME: can we do scheduling with zero overhead?
+var fqueue chan func()
+
+func init() {
+	runtime.LockOSThread()
+
+	// FIXME: what else can we do about queue size?
+	fqueue = make(chan func(), runtime.GOMAXPROCS(0))
+}
+
+// Init initializes the functionality for running arbitrary subsequent
+// functions on a main system thread.
+//
+// Init must be called in the main package.
+func Init(run func()) {
+	done := make(chan struct{})
+	go func() {
+		defer func() {
+			// FIXME: do something about panicked f.
+			recover()
+
+			done <- struct{}{}
+		}()
+		run()
+	}()
+
+	for {
+		select {
+		case f := <-fqueue:
+			f()
+		case <-done:
+			return
+		}
+	}
+}
+
+// Call calls f on the main thread and blocks until f finishes.
+func Call(f func()) {
+	done := make(chan struct{})
+	fqueue <- func() {
+		defer func() {
+			// FIXME: do something about panicked f.
+			recover()
+
+			done <- struct{}{}
+		}()
+		f()
+	}
+	<-done
+}

mainthread_test.go

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+// Copyright 2020 The golang.design Initiative Authors.
+// All rights reserved. Use of this source code is governed
+// by a GNU GPLv3 license that can be found in the LICENSE file.
+
+package mainthread_test
+
+import (
+	"fmt"
+	"testing"
+
+	"golang.design/x/mainthread"
+)
+
+func TestMainthread(t *testing.T) {
+	mainthread.Init(func() {
+		mainthread.Call(func() {
+			// FIXME: how to test this function really runs on the main thread?
+		})
+	})
+}
+
+func BenchmarkCall(b *testing.B) {
+	f1 := func() {}
+	f2 := func() {}
+
+	mainthread.Init(func() {
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			if i%2 == 0 {
+				mainthread.Call(f1)
+			} else {
+				mainthread.Call(f2)
+			}
+		}
+	})
+}
+
+func ExampleInit() {
+	mainthread.Init(func() {
+		mainthread.Call(func() {
+			fmt.Println("from main thread")
+		})
+	})
+	// Output: from main thread
+}