[Twisted-Python] Limit on transport.write

[hz hanks]

Thank you so much for your instant reply. I guess I need much more
time to process the information. You are so helpful.

Best,
Hanks

2012/3/25 Glyph <glyph at twistedmatrix.com>:
>
> On Mar 26, 2012, at 2:21 AM, hz hanks wrote:
>
> Hi, all
>
> I'm writing a program to transfer files over Internet. Sometimes the
> files would be very big. Therefore, I'm not sure whether I could read
> a large block of data and send them via one time
> internet.protocol.transport.write(). On the other hand, does the
> function internet.protocol.transport.write() have any buffer scheme?
> If so, I could just read one line of the file each time and call that
> function. Or if you have any advice on how to transfer large amount of
> data, please let me know. Really appreciated.
>
>
> First, you want to read this
> <http://twistedmatrix.com/documents/current/core/howto/producers.html>.
>
> Second, you should understand that transport.write() will always buffer; it
> will never raise an error.  The rationale for this behavior is that if
> you've already got the data as a Python string (as you must, if you're
> calling write() with it), you have already paid the not-inconsiderable cost
> of pulling that data into your process, allocating memory for it, and
> slinging it around in Python, which probably means you've already copied it
> a few times by splitting it up, moving it around, etc.  The transport
> implementations will endeavor to not copy it around too much more (they
> generally keep a list of strings around as a buffer rather than a string
> they keep concatenating to), but they will hold on to it until they're able
> to write it.
>
> If you want to know about the state of the buffer you need to subscribe to
> it using registerProducer() - so see the above document for how to do that.
>
> -glyph
>
>
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