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

[Uwe Thiem]

On 14 June 2006 14:12, 张韡武 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.

Neither nor. ;-)

It's called "blacking IO". An app that has to wait for IO (whether it's 
reading or writing doesn't matter) doesn't get CPU until the IO resource is 
ready. Of course, the scheduler in your kernel can take your app off the CPU 
for other reasons even if the resource is ready.

Uwe

-- 
Mark Twain: I rather decline two drinks than a German adjective.
http://www.SysEx.com.na
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