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Note the importance of using sync pipes

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Chris Denton 2022-04-26 21:20:40 +01:00
parent 949b978ec9
commit 1e7c15634d
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1 changed files with 19 additions and 1 deletions
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20
library/std/src/sys/windows/process.rs
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@ -527,10 +527,25 @@ impl Stdio {
},
Stdio::MakePipe => {
// If stdin then make synchronous
// Handles that are passed to a child process must be synchronous
// because they will be read synchronously (see #95759).
// Therefore we prefer to make both ends of a pipe synchronous
// just in case our end of the pipe is passed to another process.
//
// However, we may need to read from both the child's stdout and
// stderr simultaneously when waiting for output. This requires
// async reads so as to avoid blocking either pipe.
//
// The solution used here is to make handles synchronous
// except for our side of the stdout and sterr pipes.
// If our side of those pipes do end up being given to another
// process then we use a "pipe relay" to synchronize access
// (see `Stdio::AsyncPipe` below).
let pipes = if stdio_id == c::STD_INPUT_HANDLE {
// For stdin both sides of the pipe are synchronous.
Pipes::new_synchronous(false, true)?
} else {
// For stdout/stderr our side of the pipe is async and their side is synchronous.
pipe::anon_pipe(true, true)?
};
*pipe = Some(pipes.ours);
@ -567,6 +582,9 @@ impl Stdio {
impl From<AnonPipe> for Stdio {
fn from(pipe: AnonPipe) -> Stdio {
// Note that it's very important we don't give async handles to child processes.
// Therefore if the pipe is asynchronous we must have a way to turn it synchronous.
// See #95759.
match pipe {
AnonPipe::Sync(handle) => Stdio::Handle(handle),
AnonPipe::Async(handle) => Stdio::AsyncPipe(handle),