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Optimize some functions in std::process #31618

Merged
merged 3 commits into from
Mar 10, 2016
Merged

Optimize some functions in std::process #31618

merged 3 commits into from
Mar 10, 2016

Commits on Mar 9, 2016

  1. std: Funnel read_to_end through to one location 

    This pushes the implementation detail of proxying `read_to_end` through to
`read_to_end_uninitialized` all the way down to the `FileDesc` and `Handle`
implementations on Unix/Windows. This way intermediate layers will also be able
to take advantage of this optimized implementation.

This commit also adds the optimized implementation for `ChildStdout` and
`ChildStderr`.
    @alexcrichton
    alexcrichton committed Mar 9, 2016
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  2. std: Don't always create stdin for children 

    For example if `Command::output` or `Command::status` is used then stdin is just
immediately closed. Add an option for this so as an optimization we can avoid
creating pipes entirely.

This should help reduce the number of active file descriptors when spawning
processes on Unix and the number of active handles on Windows.
    @alexcrichton
    alexcrichton committed Mar 9, 2016
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  3. std: Don't spawn threads in wait_with_output 

    Semantically there's actually no reason for us to spawn threads as part of the
call to `wait_with_output`, and that's generally an incredibly heavyweight
operation for just reading a few bytes (especially when stderr probably rarely
has bytes!). An equivalent operation in terms of what's implemented today would
be to just drain both pipes of all contents and then call `wait` on the child
process itself.

On Unix we can implement this through some convenient use of the `select`
function, whereas on Windows we can make use of overlapped I/O. Note that on
Windows this requires us to use named pipes instead of anonymous pipes, but
they're semantically the same under the hood.
    @alexcrichton
    alexcrichton committed Mar 9, 2016
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