Python issue 21247: Fix a race condition in test_send_signal() of asyncio
Python issue 21247: Fix a race condition in test_send_signal() of asyncio

Add a basic synchronization mechanism to wait until the child process is ready
before sending it a signal.

1st1/asyncio,ajdavis/asyncio,gvanrossum/asyncio,Martiusweb/asyncio,gsb-eng/asyncio,haypo/trollius,ajdavis/asyncio,gsb-eng/asyncio,1st1/asyncio,haypo/trollius,vxgmichel/asyncio,vxgmichel/asyncio,manipopopo/asyncio,jashandeep-sohi/asyncio,fallen/asyncio,jashandeep-sohi/asyncio,gvanrossum/asyncio,gvanrossum/asyncio,manipopopo/asyncio,vxgmichel/asyncio,Martiusweb/asyncio,Martiusweb/asyncio,fallen/asyncio,manipopopo/asyncio,1st1/asyncio,fallen/asyncio,gsb-eng/asyncio,ajdavis/asyncio,jashandeep-sohi/asyncio,haypo/trollius