runtime: run init on main thread

Fixes #3125.

R=golang-dev, r, minux.ma
CC=golang-dev
https://golang.org/cl/5714049

src/pkg/runtime/runtime_linux_test.go

@@ -0,0 +1,29 @@
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime_test
+
+import (
+	. "runtime"
+	"syscall"
+	"testing"
+)
+
+var pid, tid int
+
+func init() {
+	// Record pid and tid of init thread for use during test.
+	// The call to LockOSThread is just to exercise it;
+	// we can't test that it does anything.
+	// Instead we're testing that the conditions are good
+	// for how it is used in init (must be on main thread).
+	pid, tid = syscall.Getpid(), syscall.Gettid()
+	LockOSThread()
+}
+
+func TestLockOSThread(t *testing.T) {
+	if pid != tid {
+		t.Fatalf("pid=%d but tid=%d", pid, tid)
+	}
+}