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writable stream _write and _writev #28408
Description
Version: v12.4.0 or v10.15.3
Platform: Linux 4.15.0-51-generic #55~16.04.1-Ubuntu SMP Thu May 16 09:24:37 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Subsystem: Stream Duplex, Object mode, piped into itself.
The documentation says that when I implement _writev method, it will receive chunks of data available in the buffer.
What I actually see is that both _write and _writev methods are used simultaneously.
If _write is fast enough to process the buffer until it fills up to more than one object, then only _write is used. Otherwise, for the first object in the buffer _write will be used, and the rest will be sent to _writev.
Example:
DEBUG: Calling _write with 1
DEBUG: Calling _writev with 15
DEBUG: Calling _write with 1
DEBUG: Pushing null to readable
DEBUG: Calling _writev with 15
DEBUG: Calling _write with 1
DEBUG: Calling _writev with 2
DEBUG: Writable final
DEBUG: _writev 16, _write 16
DEBUG: Read 243, Written 243
Is this an expected behavior? I was assuming that when _writev method is implemented, it will be used exclusively.
Thanks
Activity
lpinca commentedon Jul 10, 2019
This is by design. The first chunk is written with
_write(). When the write is complete, buffered chunks, if available, will be written all at once with_writev().addaleax commentedon Jul 10, 2019
I’ve added the
doclabel because this is indeed missing from the documentation and I think a PR to address that would make sense.docs: fix description of _writev()
asbillings07 commentedon Oct 4, 2019
Does this still need to be worked on? If so I'd like to take it.
ronag commentedon Oct 8, 2019
This might be relevant #29639
addaleax commentedon Oct 8, 2019
@asbillings07 You might want to look at #28690 – it’s an open PR for this, where @tyof45 started working on it but that has kind of stalled out. I’d suggest waiting a short time to see if there’s any movement in that PR, and if not, you can feel free to open a new one.
asbillings07 commentedon Oct 8, 2019
@addaleax Okay sounds good.
doc: explain _writev() API
doc: explain _writev() API
doc: explain _writev() API