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-rw-r--r--lib/kernel/doc/src/inet.xml51
1 files changed, 35 insertions, 16 deletions
diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml
index e1b0b34888..fb8bf32978 100644
--- a/lib/kernel/doc/src/inet.xml
+++ b/lib/kernel/doc/src/inet.xml
@@ -456,47 +456,66 @@ fe80::204:acff:fe17:bf38
<p>Sets one or more options for a socket. The following options
are available:</p>
<taglist>
- <tag><c>{active, true | false | once}</c></tag>
+ <tag><c>{active, true | false | once | N}</c></tag>
<item>
<p>If the value is <c>true</c>, which is the default,
everything received from the socket will be sent as
messages to the receiving process. If the value is
<c>false</c> (passive mode), the process must explicitly
- receive incoming data by calling <c>gen_tcp:recv/2,3</c>
- or <c>gen_udp:recv/2,3</c> (depending on the type of
- socket).</p>
+ receive incoming data by calling
+ <seealso marker="gen_tcp#recv/2"><c>gen_tcp:recv/2,3</c></seealso>,
+ <seealso marker="gen_udp#recv/2"><c>gen_udp:recv/2,3</c></seealso>
+ or <seealso marker="gen_sctp#recv/1"><c>gen_sctp:recv/1,2</c></seealso>
+ (depending on the type of socket).</p>
<p>If the value is <c>once</c> (<c>{active, once}</c>),
<em>one</em> data message from the socket will be sent
to the process. To receive one more message,
<c>setopts/2</c> must be called again with the
<c>{active, once}</c> option.</p>
- <p>When using <c>{active, once}</c>, the socket changes
- behaviour automatically when data is received. This can
- sometimes be confusing in combination with connection
- oriented sockets (i.e. <c>gen_tcp</c>) as a socket with
- <c>{active, false}</c> behaviour reports closing
+ <p>If the value is an integer <c>N</c> in the range -32768 to 32767
+ (inclusive), the value is added to the socket's count of data
+ messages sent to the controlling process. A socket's default
+ message count is 0. If a negative value is specified and its
+ magnitude is equal to or greater than the socket's current
+ message count, the socket's message count is set to 0. Once
+ the socket's message count reaches 0, either due to sending
+ received data messages to the process or by being explicitly set,
+ the process is then notified by a special message, specific to
+ the type of socket, that the socket has entered passive
+ mode. Once the socket enters passive mode, to receive more
+ messages <c>setopts/2</c> must be called again to set the
+ socket back into an active mode.</p>
+ <p>When using <c>{active, once}</c> or <c>{active, N}</c>, the
+ socket changes behaviour automatically when data is received.
+ This can sometimes be confusing in combination with
+ connection-oriented sockets (i.e. <c>gen_tcp</c>) as a socket
+ with <c>{active, false}</c> behaviour reports closing
differently than a socket with <c>{active, true}</c>
behaviour. To make programming easier, a socket where
the peer closed and this was detected while in
<c>{active, false}</c> mode, will still generate the
message
- <c>{tcp_closed,Socket}</c> when set to <c>{active, once}</c> or <c>{active, true}</c> mode. It is therefore
+ <c>{tcp_closed,Socket}</c> when set to <c>{active, once}</c>,
+ <c>{active, true}</c> or <c>{active, N}</c> mode. It is therefore
safe to assume that the message
<c>{tcp_closed,Socket}</c>, possibly followed by socket
port termination (depending on the <c>exit_on_close</c>
option) will eventually appear when a socket changes
back and forth between <c>{active, true}</c> and
- <c>{active, false}</c> mode. However,
+ <c>{active, false}</c> mode. However,
<em>when</em> peer closing is detected is all up to the
underlying TCP/IP stack and protocol.</p>
- <p>Note that <c>{active,true}</c> mode provides no flow
+ <p>Note that <c>{active, true}</c> mode provides no flow
control; a fast sender could easily overflow the
- receiver with incoming messages. Use active mode only if
+ receiver with incoming messages. The same is true of
+ <c>{active, N}</c> mode while the message count is greater
+ than zero. Use active mode only if
your high-level protocol provides its own flow control
(for instance, acknowledging received messages) or the
- amount of data exchanged is small. <c>{active,false}</c>
- mode or use of the <c>{active, once}</c> mode provides
- flow control; the other side will not be able send
+ amount of data exchanged is small. <c>{active, false}</c>
+ mode, use of the <c>{active, once}</c> mode or <c>{active, N}</c>
+ mode with values of <c>N</c> appropriate for the application
+ provides flow control; the other side will not be able send
faster than the receiver can read.</p>
</item>