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Refine Q9/A9.

This commit is contained in:
Michael Kerrisk 2008-02-28 13:49:29 +00:00
parent 7fb5cf0fb6
commit f11af7daa2
1 changed files with 18 additions and 20 deletions
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@ -377,34 +377,32 @@ when using the
flag (edge-triggered behavior) ?
.TP
.B A9
The answer depends on whether the file descriptor refers to a
stream-oriented file, or to a packet/token-oriented file.
.sp
For a stream oriented file (pipe, FIFO, stream socket): no you don't.
Receiving an event from
.BR epoll_wait (2)
should suggest to you that such file descriptor is ready
for the requested I/O operation.
You have simply to consider it ready until you will receive the
next
should suggest to you that such
file descriptor is ready for the requested I/O operation.
You have simply to consider it ready until you receive the next
.BR EAGAIN .
When and how you will use such file descriptor is entirely up
to you.
Also, the condition that the read/write I/O space is exhausted can
be detected by checking the amount of data read from / written to the target
file descriptor.
When and how you will use the file descriptor is entirely up to you.
.sp
For stream oriented files (e.g., pipe, FIFO, stream socket), the
condition that the read/write I/O space is exhausted can also be detected by
checking the amount of data read from / written to the target file
descriptor.
For example, if you call
.BR read (2)
by asking to read a certain amount of data and
by asking to read a certain amount of data and
.BR read (2)
returns a lower number of bytes,
you can be sure of having exhausted the read
I/O space for such file descriptor.
The same is true when writing using
returns a lower number of bytes, you
can be sure of having exhausted the read I/O space for the file
descriptor.
The same is true when writing using
.BR write (2).
.sp
For a packet/token-oriented file (e.g., datagram socket,
terminal in canonical mode): yes you do.
For packet/token oriented files (e.g., datagram socket,
terminal in canonical mode), you need to continue to read/write until
.BR EAGAIN ,
in order to detect the end of the read/write I/O space.
.SS Possible Pitfalls and Ways to Avoid Them
.TP
.B o Starvation (edge-triggered)