pojmenovan roura

[Pavel Kankovsky]

On Mon, 8 Dec 1997, Ondrej Kamenik wrote:

> 1) zapisovatel vytvori pojmenovanou rouru 
> 2) ctenar ji otevre ke cteni bez blokovani, tedy:
>       fifo=open(cesta,O_RDONLY|O_NONBLOCK);
> 3) zacne cist volanim:
>       char c;
>       read(fifo,&c,1);
> tady bych ocekaval, ze read vrati -1 a v errno bude  EWOULDBLOCK (nebo
> EAGAIN). Ale vono nic, volani read nezkolabuje a v c se mi objevovala 0.
ehmm---nevracel read() nulu?

> Otazka zni: proc to nefunguje tak, jak by clovek (kamenik) cekal?

semantika fifo je trochu zvlastni, kdybych tvrdil, ze ji rozumim, tak
bych kecal; ale podival jsem se do "Single User Specification 2"
(viz http://www.rdg.opengroup.org/)

When attempting to read from an empty pipe or FIFO: 

   *  If no process has the pipe open for writing, read() will return 0 to
      indicate end-of-file. 

   *  If some process has the pipe open for writing and O_NONBLOCK is set,
      read() will return -1 and set errno to [EAGAIN]. 

   *  If some process has the pipe open for writing and O_NONBLOCK is
      clear, read() will block the calling thread until some data is
      written or the pipe is closed by all processes that had the pipe
      open for writing. 


--Pavel Kankovsky aka Peak (troja.mff.cuni.cz network administration)
          [ Boycott Microsoft -- http://www.vcnet.com/bms ]