Originální popis anglicky:
sockatmark - determine whether a socket is at the out-of-band mark
Návod, kniha: POSIX Programmer's Manual
#include <sys/socket.h>
int sockatmark(int
s);
The
sockatmark() function shall determine whether the socket specified by
the descriptor
s is at the out-of-band data mark (see the System
Interfaces volume of IEEE Std 1003.1-2001, Section 2.10.12,
Socket Out-of-Band State). If the protocol for the socket supports out-of-band
data by marking the stream with an out-of-band data mark, the
sockatmark() function shall return 1 when all data preceding the mark
has been read and the out-of-band data mark is the first element in the
receive queue. The
sockatmark() function shall not remove the mark from
the stream.
Upon successful completion, the
sockatmark() function shall return a
value indicating whether the socket is at an out-of-band data mark. If the
protocol has marked the data stream and all data preceding the mark has been
read, the return value shall be 1; if there is no mark, or if data precedes
the mark in the receive queue, the
sockatmark() function shall return
0. Otherwise, it shall return a value of -1 and set
errno to indicate
the error.
The
sockatmark() function shall fail if:
- EBADF
- The s argument is not a valid file descriptor.
- ENOTTY
- The s argument does not specify a descriptor for a
socket.
The following sections are informative.
None.
The use of this function between receive operations allows an application to
determine which received data precedes the out-of-band data and which follows
the out-of-band data.
There is an inherent race condition in the use of this function. On an empty
receive queue, the current read of the location might well be at the
"mark", but the system has no way of knowing that the next data
segment that will arrive from the network will carry the mark, and
sockatmark() will return false, and the next read operation will
silently consume the mark.
Hence, this function can only be used reliably when the application already
knows that the out-of-band data has been seen by the system or that it is
known that there is data waiting to be read at the socket (via SIGURG or
select()). See
Socket Receive Queue ,
Socket Out-of-Band Data
State ,
Signals , and
pselect() for details.
The
sockatmark() function replaces the historical SIOCATMARK command to
ioctl() which implemented the same functionality on many
implementations. Using a wrapper function follows the adopted conventions to
avoid specifying commands to the
ioctl() function, other than those now
included to support XSI STREAMS. The
sockatmark() function could be
implemented as follows:
#include <sys/ioctl.h>
int sockatmark(int s)
{
int val;
if (ioctl(s,SIOCATMARK,&val)==-1)
return(-1);
return(val);
}
The use of [ENOTTY] to indicate an incorrect descriptor type matches the
historical behavior of SIOCATMARK.
None.
pselect() ,
recv() ,
recvmsg() , the Base Definitions
volume of IEEE Std 1003.1-2001,
<sys/socket.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
