stream: don't deadlock duplexpair #29836
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If nothing is buffered then _read will not be called and the callback will not invoked, effectivly deadlocking. Fixes: nodejs#29758
test/common/duplexpair.js
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| this[kOtherSide].push(chunk); | ||
| if (!this[kOtherSide].readableLength) { |
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If we have no readableLength _read will never be called.
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Just to be clear that I’m not misunderstanding – this is because _read() was already called?
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But wouldn’t .push() schedule another ._read() call, because the readable side’s buffer is empty once the data from .push() is used?
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@addaleax push(chunk) should not schedule another read if push(null) is called in the same tick.
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The current implementation disregards this invariant of Readable.
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This made me consider why push(null) is called before _read. Could be that _final is called before all writes having finished. Let me check.
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no, it simply that an empty push will not trigger another read, as it is sensible to assume that if we couldn't push data then there is no data
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I mean, that kind of makes sense, but it’s also weird that .push() with an empty chunk leads to different behaviour than .push() with a non-empty chunk…
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Yea, I've been trying to get my head around it for a few days. But as you write, it's weird but makes sense. The alternative is more confusing and leads to other problems such as livelocks.
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This is basically the workaround I suggested in #29758 (comment). |
Yep, it took me a bit longer to come to the same conclusion. |
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To rephrase #29649 (comment): this looks good, I'm just surprised it requires a fix to the DuplexPair implementation (the part I was hoping to not change, since that code is copied in so many places)—but I guess that makes sense. |
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If nothing is buffered then _read will not be called and the callback will not be invoked, effectivly deadlocking. Fixes: #29758 PR-URL: #29836 Refs: #29649 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Minwoo Jung <[email protected]>
PR-URL: #29836 Refs: #29758 Refs: #29649 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Minwoo Jung <[email protected]>
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Landed in 0b495a8...28c3a9d |
If nothing is buffered then _read will not be called and the callback will not be invoked, effectivly deadlocking. Fixes: #29758 PR-URL: #29836 Refs: #29649 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Minwoo Jung <[email protected]>
PR-URL: #29836 Refs: #29758 Refs: #29649 Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Minwoo Jung <[email protected]>
If nothing is buffered then _read will not be called and the callback will not invoked, effectivly deadlocking.
Fixes: #29758
Refs: #29649
Checklist
make -j4 test(UNIX), orvcbuild test(Windows) passes