Demonstrate best practice for feeding stdin of a child processes
Documentation change.
It's possible to create a deadlock with stdin/stdout I/O on a single thread:
* the child process may fill its stdout buffer, and have to wait for the parent process to read it,
* but the parent process may be waiting until its stdin write finishes before reading the stdout.
Therefore, the parent process should use separate threads for writing and reading.
These examples are not deadlocking in practice, because they use short strings, but I think it's better to demonstrate code that works even for long writes. The problem is non-obvious and tricky to debug (it seems that even libstd has a similar issue: #45572).
This also demonstrates how to use stdio with threads: it's not obvious that `.take()` can be used to avoid fighting with the borrow checker.
I've checked that the modified examples run fine.
It's possible to create a deadlock with stdin/stdout I/O on a single thread:
* the child process may fill its stdout buffer, and have to wait for the parent process to read it,
* but the parent process may be waiting until its stdin write finishes before reading the stdout.
Therefore, the parent process should use separate threads for writing and reading.
The use of `ExitStatus` as the Rust type name for a Unix *wait
status*, not an *exit status*, is very confusing, but sadly probably
too late to change.
This area is confusing enough in Unix already (and many programmers
are already confuxed). We can at least document it.
I chose *not* to mention the way shells like to exit with signal
numbers, thus turning signal numbers into exit statuses. This is only
relevant for Rust programs using `std::process` if they run shells.
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Drop support for all cloudabi targets
`cloudabi` is a tier-3 target, and [it is no longer being maintained upstream][no].
This PR drops supports for cloudabi targets. Those targets are:
* aarch64-unknown-cloudabi
* armv7-unknown-cloudabi
* i686-unknown-cloudabi
* x86_64-unknown-cloudabi
Since this drops supports for a target, I'd like somebody to tag `relnotes` label to this PR.
Some other issues:
* The tidy exception for `cloudabi` crate is still remained because
* `parking_lot v0.9.0` and `parking_lot v0.10.2` depends on `cloudabi v0.0.3`.
* `parking_lot v0.11.0` depends on `cloudabi v0.1.0`.
[no]: https://github.com/NuxiNL/cloudabi#note-this-project-is-unmaintained
deny(unsafe_op_in_unsafe_fn) in libstd/process.rs
The libstd/process.rs part of #73904 . Wraps the two calls to an unsafe fn Initializer::nop() in an unsafe block.
Will have to wait for #73909 to be merged, because of the feature in the libstd/lib.rs
As a relative beginner, it took a while for me to figure out I could just steal the references to avoid partially moving the child and thus retain ability to call functions on it (and store it in structs etc).
