1sockatmark(3XNET)X/Open Networking Services Library Functionssockatmark(3XNET)
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NAME

6       sockatmark - determine whether a socket is at the out-of-band mark
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SYNOPSIS

9       cc [ flag ... ] file ... -lxnet [ library ... ]
10       #include <sys/socket.h>
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12       int sockatmark(int s);
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DESCRIPTION

16       The  sockatmark()  function  determines whether the socket specified by
17       the descriptor s is at the out-of-band data mark. If the  protocol  for
18       the socket supports out-of-band data by marking the stream with an out-
19       of-band data mark, the sockatmark() function returns 1  when  all  data
20       preceding  the  mark has been read and the out-of-band data mark is the
21       first element in the receive queue. The sockatmark() function does  not
22       remove the mark from the stream.
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RETURN VALUES

25       Upon  successful  completion, the sockatmark() function returns a value
26       indicating whether the socket is at an out-of-band data  mark.  If  the
27       protocol has marked the data stream and all data preceding the mark has
28       been read, the return value is 1. If there is no mark, or if data  pre‐
29       cedes  the mark in the receive queue, the sockatmark() function returns
30       0. Otherwise, it returns −1 and sets errno to indicate the error.
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ERRORS

33       The sockatmark() function will fail if:
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35       EBADF     The s argument is not a valid file descriptor.
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38       ENOTTY    The s argument does not specify a descriptor for a socket.
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USAGE

42       The use of this function between receive operations allows an  applica‐
43       tion to determine which received data precedes the out-of-band data and
44       which follows the out-of-band data.
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47       There is an inherent race condition in the use of this function. On  an
48       empty  receive queue, the current read of the location might well be at
49       the "mark", but the system has no way of knowing  that  the  next  data
50       segment  that  will  arrive  from  the network will carry the mark, and
51       sockatmark() will return  false,  and  the  next  read  operation  will
52       silently consume the mark.
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55       Hence,  this  function  can  only be used reliably when the application
56       already knows that the out-of-band data has been seen by the system  or
57       that  it  is known that there is data waiting to be read at the socket,
58       either by SIGURG or select(3C).
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ATTRIBUTES

61       See attributes(5) for descriptions of the following attributes:
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66       ┌─────────────────────────────┬─────────────────────────────┐
67       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
68       ├─────────────────────────────┼─────────────────────────────┤
69       │Interface Stability          │Standard                     │
70       ├─────────────────────────────┼─────────────────────────────┤
71       │MT-Level                     │Safe                         │
72       └─────────────────────────────┴─────────────────────────────┘
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SEE ALSO

75       recv(3XNET), recvmsg(3XNET), select(3C), attributes(5), standards(5)
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79SunOS 5.11                        1 Oct 2003                 sockatmark(3XNET)
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