1sockatmark(3XNET)X/Open Networking Services Library Functionssockatmark(3XNET)
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6 sockatmark - determine whether a socket is at the out-of-band mark
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9 cc [ flag ... ] file ... -lxnet [ library ... ]
10 #include <sys/socket.h>
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12 int sockatmark(int s);
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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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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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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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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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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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75 recv(3XNET), recvmsg(3XNET), select(3C), attributes(5), standards(5)
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79SunOS 5.11 1 Oct 2003 sockatmark(3XNET)