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Expand documentation of process::exit and exec #38518

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Feb 5, 2017
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Expand documentation of process::exit and exec #38518

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21 changes: 19 additions & 2 deletions src/libstd/process.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -924,10 +924,27 @@ impl Child {
///
/// # Examples
///
/// Due to this function’s behavior regarding destructors, a conventional way
/// to use the function is to extract the actual computation to another
/// function and compute the exit code from its return value:
///
/// ```
/// use std::process;
/// use std::io::{self, Write};
///
/// fn run_app() -> Result<(), ()> {
/// // Application logic here
/// Ok(())
/// }
///
/// process::exit(0);
/// fn main() {
/// ::std::process::exit(match run_app() {
/// Ok(_) => 0,
/// Err(err) => {
/// writeln!(io::stderr(), "error: {:?}", err).unwrap();
/// 1
/// }
/// });
/// }
/// ```
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What do you think about this as an example:

use std::io::{self, Write};
use std::process;

fn run_app() -> Result<(), ()> {
    // Your application logic here
    Ok(())
}

fn main() {
    process::exit(match run_app() {
        Ok(_) => 0,
        Err(_) => 1,
    });
}

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I personally prefer to not include an import for only one use of a function. I incorporated some of the other changes.

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Why are you printing the error if the error type is ()?

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I suppose I can see why, but it does seem unrelated to the point of this example. Not a big deal.

///
/// Due to [platform-specific behavior], the exit code for this example will be
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10 changes: 10 additions & 0 deletions src/libstd/sys/unix/ext/process.rs
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Expand Up @@ -67,10 +67,20 @@ pub trait CommandExt {
/// an error indicating why the exec (or another part of the setup of the
/// `Command`) failed.
///
/// `exec` not returning has the same implications as calling
/// [`process::exit`] – no destructors on the current stack or any other
/// thread’s stack will be run. Therefore, it is recommended to only call
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Would it be more accurate to replace "any other thread's" with "child thread's"?

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No. “Child thread” makes sense in relation to “main thread”, but you can call process::exit on any thread you want.

/// `exec` at a point where it is fine to not run any destructors. Note,
/// that the `execvp` syscall independently guarantees that all memory is
/// freed and all file descriptors with the `CLOEXEC` option (set by default
/// on all file descriptors opened by the standard library) are closed.
///
/// This function, unlike `spawn`, will **not** `fork` the process to create
/// a new child. Like spawn, however, the default behavior for the stdio
/// descriptors will be to inherited from the current process.
///
/// [`process::exit`]: ../../../process/fn.exit.html
///
/// # Notes
///
/// The process may be in a "broken state" if this function returns in
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