sockatmark man page on SmartOS

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

       cc [ flag ... ] file ... -lxnet [ library ... ]
       #include <sys/socket.h>

       int sockatmark(int s);

       The  sockatmark()  function  determines whether the socket specified by
       the descriptor s is at the out-of-band data mark. 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 returns 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 does  not
       remove the mark from the stream.

       Upon  successful	 completion, the sockatmark() function returns 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 is 1. If there is no mark, or if data  pre‐
       cedes  the mark in the receive queue, the sockatmark() function returns
       0. Otherwise, it returns −1 and sets errno to indicate the error.

       The sockatmark() function will fail if:

		 The s argument is not a valid file descriptor.

		 The s argument does not specify a descriptor for a socket.

       The use of this function between receive operations allows an  applica‐
       tion 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,
       either by SIGURG or select(3C).

       See attributes(5) for descriptions of the following attributes:

       │Interface Stability │ Standard	      │
       │MT-Level	    │ Safe	      │

       recv(3XNET), recvmsg(3XNET), select(3C), attributes(5), standards(5)

				  Oct 1, 2003		     SOCKATMARK(3XNET)

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