`runtime/cgo: could not obtain pthread_keys' on darwin/amd64

hello.go

// file: plugins/hello/hello.go
// $ go build -o libhello.so -buildmode=c-shared hello.go
package main

import "C"

import (
	"log"
)

//export Hello
func Hello() int {
	log.Println("Hello")
	return 200
}

func init() {
	log.Println("loaded")
}

func main() {
}

main.go

// file: main.go
package main

import "C"

import (
	"bitbucket.org/binet/go-ffi/pkg/ffi"
	"fmt"
)

func main() {
	lib, err := ffi.NewLibrary("./plugins/hello/libhello.so")
	if err != nil {
		panic(err)
	}
	defer lib.Close()

	fn, err := lib.Fct("Hello", ffi.Int, []ffi.Type{})
	if err != nil {
		panic(err)
	}
	fmt.Printf("%#v\n", fn().Int())
}

here's my environment

~/src/test❯ uname -sv
Darwin Darwin Kernel Version 14.5.0: Wed Jul 29 02:26:53 PDT 2015; root:xnu-2782.40.9~1/RELEASE_X86_64
~/src/test❯ go version
go version go1.5.1 darwin/amd64
~/src/test❯ brew info libffi
libffi: stable 3.0.13 (bottled), HEAD
Portable Foreign Function Interface library
https://sourceware.org/libffi/

This formula is keg-only.
Some formulae require a newer version of libffi.

/usr/local/Cellar/libffi/3.0.13 (13 files, 388K)
  Built from source
From: https://github.com/Homebrew/homebrew/blob/master/Library/Formula/libffi.rb
==> Caveats
This formula is keg-only, which means it was not symlinked into /usr/local.

Some formulae require a newer version of libffi.

Generally there are no consequences of this for you. If you build your
own software and it requires this formula, you'll need to add to your
build variables:

    LDFLAGS:  -L/usr/local/opt/libffi/lib

~/src/test❯ tree
.
├── main.go
└── plugins
    └── hello
        ├── hello.go
        ├── libhello.h
        └── libhello.so

2 directories, 4 files