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32 .\" @(#)accept.2 8.2 (Berkeley) 12/11/93
40 .Nd accept a connection on a socket
42 .Fd #include <sys/types.h>
43 .Fd #include <sys/socket.h>
45 .Fn accept "int s" "struct sockaddr *addr" "int *addrlen"
49 is a socket that has been created with
51 bound to an address with
53 and is listening for connections after a
58 extracts the first connection request
59 on the queue of pending connections, creates
60 a new socket with the same properties of
62 and allocates a new file descriptor
63 for the socket. If no pending connections are
64 present on the queue, and the socket is not marked
67 blocks the caller until a connection is present.
68 If the socket is marked non-blocking and no pending
69 connections are present on the queue,
71 returns an error as described below.
74 to accept more connections. The original socket
80 is a result parameter that is filled in with
81 the address of the connecting entity,
82 as known to the communications layer.
83 The exact format of the
85 parameter is determined by the domain in which the communication
89 is a value-result parameter; it should initially contain the
90 amount of space pointed to by
92 on return it will contain the actual length (in bytes) of the
95 is used with connection-based socket types, currently with
100 a socket for the purposes of doing an
102 by selecting it for read.
104 For certain protocols which require an explicit confirmation,
111 as merely dequeueing the next connection
112 request and not implying confirmation.
113 Confirmation can be implied by a normal read or write on the new
114 file descriptor, and rejection can be implied by closing the
117 One can obtain user connection request data without confirming
118 the connection by issuing a
127 Similarly, one can provide user connection rejection information
130 call with providing only the control information,
133 .Sh IMPLEMENTATION NOTES
135 In the non-threaded library
137 is implemented as the
141 In the threaded library, the
143 syscall is assembled to
144 .Fn _thread_sys_accept
147 is implemented as a function which locks
149 for read and write, then calls
150 .Fn _thread_sys_accept .
152 .Fn _thread_sys_accept
153 would block, a context switch is performed. Before returning,
159 The call returns \-1 on error. If it succeeds, it returns a non-negative
160 integer that is a descriptor for the accepted socket.
165 .Bl -tag -width EWOULDBLOCK
167 The descriptor is invalid.
171 operation was interrupted.
173 The per-process descriptor table is full.
175 The system file table is full.
177 The descriptor references a file, not a socket.
180 has not been called on the socket descriptor.
184 parameter is not in a writable part of the
186 .It Bq Er EWOULDBLOCK
187 The socket is marked non-blocking and no connections
188 are present to be accepted.