This implements set_timeout() for std::io::Process which will affect wait()
operations on the process. This follows the same pattern as the rest of the
timeouts emerging in std::io::net.
The implementation was super easy for everything except libnative on unix
(backwards from usual!), which required a good bit of signal handling. There's a
doc comment explaining the strategy in libnative. Internally, this also required
refactoring the "helper thread" implementation used by libnative to allow for an
extra helper thread (not just the timer).
This is a breaking change in terms of the io::Process API. It is now possible
for wait() to fail, and subsequently wait_with_output(). These two functions now
return IoResult<T> due to the fact that they can time out.
Additionally, the wait_with_output() function has moved from taking `&mut self`
to taking `self`. If a timeout occurs while waiting with output, the semantics
are undesirable in almost all cases if attempting to re-wait on the process.
Equivalent functionality can still be achieved by dealing with the output
handles manually.
[breaking-change]
cc #13523
This commit has an implementation of the previous commit's timeout interface for
I/O objects on unix platforms. For implementation details, see the large comment
at the end of libnative/io/net.rs which talks about the general strategy taken.
Thankfully, all of these implementations can share code because they're
performing all the same operations.
This commit does not implement timeouts for named pipes on windows, only tcp/udp
objects on windows (which are quite similar to their unix equivalents).
This adds a `TcpStream::connect_timeout` function in order to assist opening
connections with a timeout (cc #13523). There isn't really much design space for
this specific operation (unlike timing out normal blocking reads/writes), so I
am fairly confident that this is the correct interface for this function.
The function is marked #[experimental] because it takes a u64 timeout argument,
and the u64 type is likely to change in the future.
