Accessing process.stdin hangs on Windows

Let's consider this example project consisting of 3 files:

// main.js
var spawn = require('child_process').spawn;
var middle = spawn(process.execPath, ['middle.js'], {
    'stdio': 'pipe'
});

middle.stdout.on('data', function(data) {
    process.stdout.write('stdout from middle: ' + data);
});

middle.stderr.on('data', function(data) {
    process.stdout.write('stderr from middle: ' + data);
});

middle.on('close', function(code) {
    process.stdout.write('middle process finished with exit code ' + code);
});

// middle.js
var spawn = require('child_process').spawn;
var stdin = process.stdin;
console.log('middle: isatty(stdin)=' +require('tty').isatty(stdin));
spawn(process.execPath, ['child.js'], {
    'stdio': [process.stdin, process.stdout, process.stderr]
});

// child.js
console.log('child: accessing process.stdin');
console.log('child: done successfully ' + process.stdin);

Running node main.js in cmd.exe should normally output these lines and exit

stdout from middle: middle: isatty(stdin)=false
stdout from middle: child: accessing process.stdin
stdout from middle: child: done successfully [object Object]
middle process finished with exit code 0

However, from time to time it outputs only two first lines and hangs:

stdout from middle: middle: isatty(stdin)=false
stdout from middle: child: accessing process.stdin

The hanging is caused by accessing process.stdin in child.js. Please note it works fine if process.stdin is replaced with 'pipe' here:

// middle.js
...
spawn(process.execPath, ['child.js'], {
    'stdio': ['pipe', process.stdout, process.stderr]
});

Node.js v7.4.0
OS Windows 10

/cc @nodejs/platform-windows

See also #5620

Does changing the spawn option to 'inherit' for stdin make any difference?

@Fishrock123

@Fishrock123 If you meant changing middle.js, like

// middle.js
...
spawn(process.execPath, ['child.js'], {
    'stdio': 'inherit'
});

Then, no, it doesn't make any difference for me.
As for changing main.js, it's will change the behavior, yes. However, middle.js is executed with piped standard streams (not tty) in my environment, so it's impossible to make this change for me.

If you meant changing middle.js, like

Correct. Just making sure there wasn't any hidden Windows logic in inherit.

win, pipe: avoid synchronous pipe deadlocks

@bzoz

@bzoz Is fixing this likely blocked by until libuv/libuv#1273 or equivalent lands in libuv and the appropriate version of libuv gets upstreamed to our deps directory?

Yes

win, pipe: avoid synchronous pipe deadlocks

test: stdio pipe behavior tests

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Accessing process.stdin hangs on Windows #10836

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Accessing process.stdin hangs on Windows #10836

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addaleax commented on Jan 16, 2017

seishun commented on Jan 16, 2017

Fishrock123 commented on Jan 16, 2017

segrey commented on Jan 16, 2017

Fishrock123 commented on Jan 16, 2017

Trott commented on Jul 15, 2017

bzoz commented on Jul 17, 2017

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