Use thread local to make environment threadsafe

[suned]

Use thread local to make environment threadsafe

[suned]

Each thread must define their own environment
i.e this should fail:

def run():
     Dependent().dependency  # raises NoEnvironment

def run_with_own_env():
    with Environment():
        Dependent().dependency  # ok

with Environment():
    Thread(target=run).start()
    Thread(target=run_with_own_env()).start()