gdb hangs when it calls tcsetpgrp.

[jojelino]

I was using gdb for debugging ffmpeg raising SIGFPE. but gdb hangs after 
entering command among of s,n,si,ni.
gdb has same pgrp over pgrp of debuggee. when tcsetpgrp is called in 
gdb, you already know it sends __SIGSETPGRP signal to suspended 
debuggee. but the debugger already suspended all thread of debuggee 
without distinguishing whether the victim thread is wait_sig or not. so 
the suspend process doesn't wake up until debugger handles debug event. 
which is the cause of hang.
Although it seems that cygwin developers have already aware of sort of 
this issue according to fhandler_termios.cc:85, so, it would be good if 
cygwin can defer sending signal that would block for sure.

--
Regards.

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