cygwin + rsync issue under Windows 7 x64

Jamie Lokier jamie at
Sun Mar 7 22:19:51 MST 2010

Wayne Davison wrote:
>    I'd imagine that both ssh and rsync start using a lot of CPU because
>    the socketpair must be indicating that it is ready for a write (or
>    read) but the actual write() (or read()) fails to return any bytes (as
>    long as errno is something like EAGAIN, EINTR, or EWOULDBLOCK, rsync
>    will try again). Â If you want to test that theory, you could add some
>    prints to rsync's io.c file near the 3 uses of EWOULDBLOCK and have it
>    output what errno it gets. Â If you get that fixed, the programs that
>    interface with a socketpair should go back to normal.

It would not be the first time Cygwin did something like that.

11.5 years ago, Cygwin32 b19.1, I found it returning EAGAIN
continuously when reading from pipes to a child process and from the
master side of a pty to a child process, while select() indicated
"ready for exception" (at least from the pty master; I don't remember
if it was that or "ready for read" from a pipe).

How interesting that sockpair() now looks like having a similar problem.

Perhaps the sockpair problem might be related to the getting stuck
people occasionally report with rsync + ssh + Cygwin ?  I.e. maybe
disabling socketpair() will fix the stuck problem too?

Maybe the next time someone encounters it, they'll google this thread,
try it and let us know how it went, thanks :)

-- Jamie

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