A race condition in IPython under Mac OS Darwin. iopub.get_msg fails unless sleep(1) is uncommented.

racecondition.py

from IPython.kernel import KernelManager

from time import sleep

def racecondition():
    km = KernelManager()
    km.start_kernel()

    kc = km.client()
    kc.start_channels()

    iopub = kc.iopub_channel
    shell = kc.shell_channel
    
    #sleep(1)

    shell.execute('print "hello world"')
    print shell.get_msg(timeout=1)
    print iopub.get_msg(timeout=1)


if __name__ == '__main__':
    racecondition()