Re: [gentoo-user] how does a pipe work? Which process wait for which one, or they don't actually wait each other?

[Devon Miller]

It's mode 2. When appB stops reading, appA will continue writing until
the pipe is full (about 4k I believe) at which time appA will block in
a write.

dcm

On 6/14/06, ÕÅí|Îä <zhangweiwu@××××××.com> wrote:
> Hello. This might be OT but I am pretty interested in this and being
> unlucky not able to find a real in-depth explanation of pipe on the
> Internet.
>
> How does pipe actually work? I mean, when there is a pipe like this:
> $ appA | appB
> What happen if appA produced output when appB is still busy processing
> the data and did not require any data from input?
>
> possibility 1) as long as appA can get the resource (CPU?), it simply
> keep outputing data, and this data is cached in memory, as long as there
> is enough memory, and will finally feed to appB when appB finished his
> business and begin to accept more data;
>
> possibility 2) as long as appB stop requiring data, appA is suspended,
> the resource goes to appB. appA is only given resource (CPU?) when appB
> finished his business and begin to accept more data;
>
> Which one is true? I know usually 1) and 2) makes no difference to most
> users, that's why the detail explanation of "1) or 2)" is so hard to
> google out.
>
> In my case appA gets the data from another host who have very short
> timeout settings, appB is used to compress the data obtained from appA.
> the compression is very difficult, usually at 30Kbps, the network is
> very fast, around 10Mbps. appB compress the data tunck by tunck, if
> Linux actually works in mode 2), the network connection is dropped when
> the interval of two tuncks of appB compressing data is longer then the
> network timeout setting. appA acutally don't know how to restart
> connection from where it was dropped, thus understanding this difference
> makes sense to me.
>
> I made several experiements and my appA and appB both works fine, but I
> don't dare to share this appA/B to others unless I get the mechnism
> understood.
>
> Thank you in advance.
>
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>
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