File: ei_connect.html

package info (click to toggle)
erlang-doc-html 1%3A11.b.2-1
links: PTS
area: main
in suites: etch, etch-m68k
size: 23,284 kB
ctags: 10,724
sloc: erlang: 505; ansic: 323; makefile: 62; perl: 61; sh: 45
file content (907 lines) | stat: -rw-r--r-- 30,677 bytes
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!-- This document was generated using DocBuilder 3.3.3 -->
<HTML>
<HEAD>
  <TITLE>ei_connect</TITLE>
  <SCRIPT type="text/javascript" src="../../../../doc/erlresolvelinks.js">
</SCRIPT>
  <STYLE TYPE="text/css">
<!--
    .REFBODY     { margin-left: 13mm }
    .REFTYPES    { margin-left: 8mm }
-->
  </STYLE>
</HEAD>
<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#FF00FF"
      ALINK="#FF0000">
<!-- refpage -->
<CENTER>
<A HREF="http://www.erlang.se">
  <IMG BORDER=0 ALT="[Ericsson AB]" SRC="min_head.gif">
</A>
<H1>ei_connect</H1>
</CENTER>

<H3>C LIBRARY</H3>
<DIV CLASS=REFBODY>
ei_connect
</DIV>

<H3>C LIBRARY SUMMARY</H3>
<DIV CLASS=REFBODY>
Communicate with distributed erlang
</DIV>

<H3>DESCRIPTION</H3>
<DIV CLASS=REFBODY>

<P> This module enables C programs to communicate with erlang nodes,
using the erlang distribution over TCP/IP.

<P> A C node appears to Erlang as a
<STRONG>hidden node</STRONG>.
That is, Erlang processes that know the name of the
C node are able to communicate with it in a normal manner, but
the node name will not appear in the listing provided by the
Erlang function <CODE>nodes/0</CODE>.

</DIV>

<H3>Timeout functions</H3>
<DIV CLASS=REFBODY>

<P> Most functions appear in a version with the suffix
<CODE>_tmo</CODE> appended to the function name. Those function take
an additional argument, a timeout in <STRONG>milliseconds</STRONG>. The
semantics is this; for each communication primitive involved in
the operation, if the primitive does not complete within the time
specified, the function will return an error and
<CODE>erl_errno</CODE> will be set to <CODE>ETIMEDOUT</CODE>. With
communication primitive is ment an operation on the socket, like
<CODE>connect</CODE>, <CODE>accept</CODE>, <CODE>recv</CODE> or <CODE>send</CODE>.

<P>Obviously the timeouts are for implementing fault tolerance,
not to keep hard realtime promises. The <CODE>_tmo</CODE> functions
are for detecting non-responsive peers and to avoid blocking on
socket operations. 

<P>A timeout value of <CODE>0</CODE> (zero), means that timeouts are
disabled. Calling a <CODE>_tmo</CODE>-function with the last argument as
<CODE>0</CODE> is therefore exactly the same thing as calling the
function without the <CODE>_tmo</CODE> suffix.

<P>As with all other ei functions, you are <STRONG>not</STRONG> expected
to put the socket in non blocking mode yourself in the program. Every
use of non blocking mode is embedded inside the timeout
functions. The socket will always be back in blocking mode after
the operations are completed (regardless of the result). To
avoid problems, leave the socket options alone. Ei will handle
any socket options that need modification.

<P>In all other senses, the <CODE>_tmo</CODE> functions inherit all 
the return values and the semantics from the functions without 
the <CODE>_tmo</CODE> suffix.

</DIV>

<H3>EXPORTS</H3>

<P><A NAME="ei_connect_init/4"><STRONG><CODE>int ei_connect_init(ei_cnode* ec, const char*
        this_node_name, const char *cookie, short creation)</CODE></STRONG></A><BR>
<A NAME="ei_connect_xinit/7"><STRONG><CODE>int ei_connect_xinit(ei_cnode* ec, const char *thishostname,
        const char *thisalivename, const char *thisnodename,
        Erl_IpAddr thisipaddr, const char *cookie,
        short creation)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      These function initializes the <CODE>ec</CODE> structure, to
         identify the node name and cookie of the server. One of them
         has to be called before other functions that works on the
         type <CODE>ei_cnode</CODE> or a file descriptor accociated with a
         connection to another node are used.
        
<P>      <CODE>ec</CODE> is a structure containing information about the
         C-node. It is used in other <CODE>ei</CODE> functions for
         connecting and receiving data.
        
<P>      <CODE>this_node_name</CODE> is the registered name of the process
         (the name before '@').
        
<P>      <CODE>cookie</CODE> is the cookie for the node.
        
<P>      <CODE>creation</CODE> identifies a specific instance of a C
         node. It can help prevent the node from receiving messages
         sent to an earlier process with the same registered name.
        
<P>      <CODE>thishostname</CODE> is the name of the machine we're running
         on. If long names are to be used, it should be fully
         qualified (i.e. <CODE>durin.erix.ericsson.se</CODE> instead of
         <CODE>durin</CODE>).
        
<P>      <CODE>thisalivename</CODE> is the registered name of the process.
        
<P>      <CODE>thisnodename</CODE> is the full name of the node,
         i.e. <CODE>einode@durin</CODE>.
        
<P>      <CODE>thispaddr</CODE> if the IP address of the host.
        
<P>      A C node acting as a server will be assigned a creation
         number when it calls <CODE>ei_publish()</CODE>.
        
<P>      A connection is closed by simply closing the socket. Refer
         to system documentation to close the socket gracefully (when
         there are outgoing packets before close).
        
<P>      This function return a negative value indicating that an error
         occurred.
        
<P>      Example 1:

        
<PRE>
int n = 0;
struct in_addr addr;
ei_cnode ec;      
addr = inet_addr(&#34;150.236.14.75&#34;);
if (ei_connect_xinit(&#38;ec,
                     &#34;chivas&#34;,
                     &#34;madonna&#34;,
                     &#34;madonna@chivas.du.etx.ericsson.se&#34;,
                     &#38;addr;
                     &#34;cookie...&#34;),
                     n++) &#60; 0) {
    fprintf(stderr,&#34;ERROR when initializing: %d&#34;,erl_errno);
    exit(-1);
}
        
</PRE>

<P>      Example 2:


<PRE>
if (ei_connect_init(&#38;ec, &#34;madonna&#34;, &#34;cookie...&#34;, n++) &#60; 0) {
    fprintf(&#34;ERROR when initializing: %d&#34;,erl_errno);
    exit(-1);
}
      
</PRE>

</DIV>

<P><A NAME="ei_connect/2"><STRONG><CODE>int ei_connect(ei_cnode* ec, char *nodename)</CODE></STRONG></A><BR>
<A NAME="ei_xconnect/3"><STRONG><CODE>int ei_xconnect(ei_cnode* ec, Erl_IpAddr adr, char *alivename)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      These functions set up a connection to an Erlang node.
        
<P>      <CODE>ei_xconnect()</CODE> requires the IP address of the remote
         host and the alive name of the remote node
         to be specified. <CODE>ei_connect()</CODE> provides an alternative
         interface, and determines the information from the node name
         provided.
        
<P>      <CODE>addr</CODE> is the 32-bit IP address of the remote host.
        
<P>      <CODE>alive</CODE> is the alivename of the remote node.
        
<P>      <CODE>node</CODE> is the name of the remote node.
        
<P>      These functions return an open file descriptor on success, or
         a negative value indicating that an error occurred --- in
         which case they will set <CODE>erl_errno</CODE> to one of:
        
<P>
<DL>

<DT>
<CODE>EHOSTUNREACH</CODE>
</DT>

<DD>
The remote host <CODE>node</CODE> is unreachable
</DD>

<DT>
<CODE>ENOMEM</CODE>
</DT>

<DD>
No more memory available.
</DD>

<DT>
<CODE>EIO</CODE>
</DT>

<DD>
I/O error.
</DD>

</DL>

<P>      Additionally, <CODE>errno</CODE> values from
         <CODE>socket</CODE><STRONG>(2)</STRONG> and <CODE>connect</CODE><STRONG>(2)</STRONG>
         system calls may be propagated into <CODE>erl_errno</CODE>.
        
<P>      Example:
        
<PRE>
#define NODE   &#34;madonna@chivas.du.etx.ericsson.se&#34;
#define ALIVE  &#34;madonna&#34;
#define IP_ADDR &#34;150.236.14.75&#34;

/*** Variant 1 ***/
int fd = ei_connect(&#38;ec, NODE);

/*** Variant 2 ***/
struct in_addr addr;
addr = inet_addr(IP_ADDR);
fd = ei_xconnect(&#38;ec, &#38;addr, ALIVE);
        
</PRE>

</DIV>

<P><A NAME="ei_connect_tmo/3"><STRONG><CODE>int ei_connect_tmo(ei_cnode* ec, char
*nodename, unsigned timeout_ms)</CODE></STRONG></A><BR>
<A NAME="ei_xconnect_tmo/4"><STRONG><CODE>int ei_xconnect_tmo(ei_cnode* ec, Erl_IpAddr
        adr, char *alivename, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_connect and ei_xconnect with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_receive/3"><STRONG><CODE>int ei_receive(int fd, unsigned
        char* bufp, int bufsize)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      This function receives a message consisting of a sequence
         of bytes in the Erlang external format.
        
<P>      <CODE>fd</CODE> is an open descriptor to an Erlang connection. It
         is obtained from a previous <CODE>ei_connect</CODE> or
         <CODE>ei_accept</CODE>.
        
<P>      <CODE>bufp</CODE> is a buffer large enough to hold the expected
         message. 
        
<P>      <CODE>bufsize</CODE> indicates the size of <CODE>bufp</CODE>.
        
<P>      If a <STRONG>tick</STRONG> occurs, i.e., the Erlang node on the
         other end of the connection has polled this node to see if it
         is still alive, the function will return <CODE>ERL_TICK</CODE> and
         no message will be placed in the buffer. Also,
         <CODE>erl_errno</CODE> will be set to <CODE>EAGAIN</CODE>.
        
<P>      On success, the message is placed in the specified buffer
         and the function returns the number of bytes actually read. On
         failure, the function returns <CODE>ERL_ERROR</CODE> and will set
         <CODE>erl_errno</CODE> to one of:
        
<P>
<DL>

<DT>
<CODE>EAGAIN</CODE>
</DT>

<DD>
Temporary error: Try again.
</DD>

<DT>
<CODE>EMSGSIZE</CODE>
</DT>

<DD>
Buffer too small.
</DD>

<DT>
<CODE>EIO</CODE>
</DT>

<DD>
I/O error.
</DD>

</DL>

</DIV>

<P><A NAME="ei_receive_tmo/4"><STRONG><CODE>int ei_receive_tmo(int fd, unsigned
        char* bufp, int bufsize, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_receive with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_receive_msg/3"><STRONG><CODE>int ei_receive_msg(int fd, erlang_msg* msg,
        ei_x_buff* x)</CODE></STRONG></A><BR>
<A NAME="ei_xreceive_msg/3"><STRONG><CODE>int ei_xreceive_msg(int fd, erlang_msg* msg,
        ei_x_buff* x)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      These functions receives a message to the buffer in
         <CODE>x</CODE>. <CODE>ei_xreceive_msg</CODE> allows the buffer in
         <CODE>x</CODE> to grow, but <CODE>ei_receive_msg</CODE> fails if the
         message is bigger than the preallocated buffer in <CODE>x</CODE>.
        
<P>      <CODE>fd</CODE> is an open descriptor to an Erlang connection.
        
<P>      <CODE>msg</CODE> is a pointer to an <CODE>erlang_msg</CODE> structure
         and contains information on the message received.
        
<P>      <CODE>x</CODE> is buffer obtained from <CODE>ei_x_new</CODE>.
        
<P>      On success, the function returns <CODE>ERL_MSG</CODE> and the
         <CODE>msg</CODE> struct will be initialized. <CODE>erlang_msg</CODE>
         is defined as follows:
        
<PRE>
typedef struct {
    long msgtype;
    erlang_pid from;
    erlang_pid to;
    char toname[MAXATOMLEN+1];
    char cookie[MAXATOMLEN+1];
    erlang_trace token;
} erlang_msg;
        
</PRE>

<P>      <CODE>msgtype</CODE> identifies the type of message, and is one of
         <CODE>ERL_SEND</CODE>, <CODE>ERL_REG_SEND</CODE>, <CODE>ERL_LINK</CODE>,
         <CODE>ERL_UNLINK</CODE> and <CODE>ERL_EXIT</CODE>.
        
<P>      If <CODE>msgtype</CODE> is <CODE>ERL_SEND</CODE> this indicates that an
         ordinary send operation has taken place, and <CODE>msg-&#62;to</CODE>
         contains the Pid of the recipient (the C-node). If
         <CODE>type</CODE> is <CODE>ERL_REG_SEND</CODE> then a registered send
         operation took place, and <CODE>msg-&#62;from</CODE> contains the Pid
         of the sender.
        
<P>      If <CODE>msgtype</CODE> is <CODE>ERL_LINK</CODE> or <CODE>ERL_UNLINK</CODE>, then
         <CODE>msg-&#62;to</CODE> and <CODE>msg-&#62;from</CODE> contain the pids of the
         sender and receipient of the link or unlink.
        
<P>      If <CODE>msgtype</CODE> is <CODE>ERL_EXIT</CODE>, then this indicates that
         a link has been broken. In this case,  <CODE>msg-&#62;to</CODE> and
         <CODE>msg-&#62;from</CODE> contain the pids of the linked processes.
        
<P>      The return value is the same as for <CODE>ei_receive</CODE>, see
         above.

</DIV>

<P><A NAME="ei_receive_msg_tmo/4"><STRONG><CODE>int ei_receive_msg_tmo(int fd, erlang_msg* msg,
        ei_x_buff* x, unsigned imeout_ms)</CODE></STRONG></A><BR>
<A NAME="ei_xreceive_msg_tmo/4"><STRONG><CODE>int ei_xreceive_msg_tmo(int fd, erlang_msg* msg,
        ei_x_buff* x, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_receive_msg and ei_xreceive_msg with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_receive_encoded/5"><STRONG><CODE>int 
        ei_receive_encoded(int fd, char **mbufp, int *bufsz, 
        erlang_msg *msg, int *msglen)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>This function is retained for compatibility with code
        generated by the interface compiler and with code following
        examples in the same application.
        
<P>In essence the function performs the same operation as
        <CODE>ei_xreceive_msg</CODE>, but instead of using an ei_x_buff, the
        function expects a pointer to a character pointer
        (<CODE>mbufp</CODE>), where the character pointer should point to a
        memory area allocated by <CODE>malloc</CODE>. The argument
        <CODE>bufsz</CODE> should be a pointer to an integer containing the
        exact size (in bytes) of the memory area. The function may
        reallocate the memory area and will in such cases put the new
        size in <CODE>*bufsz</CODE> and update <CODE>*mbufp</CODE>.
        
<P>Furthermore the function returns either ERL_TICK or the
        <CODE>msgtype</CODE> field of the <CODE>erlang_msg *msg</CODE>. The actual
        length of the message is put in <CODE>*msglen</CODE>. On error it
        will return a value <CODE>&#60; 0</CODE>.
        
<P>It is recommended to use ei_xreceive_msg instead when
        possible, for the sake of readability. The function will
        however be retained in the interface for compatibility and
        will <STRONG>not</STRONG> be removed not be removed in future releases
        without notice.

</DIV>

<P><A NAME="ei_receive_encoded_tmo/6"><STRONG><CODE>int 
        ei_receive_encoded_tmo(int fd, char **mbufp, int *bufsz, 
        erlang_msg *msg, int *msglen, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_receive_encoded with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_send/4"><STRONG><CODE>int ei_send(int fd, erlang_pid* to, char* buf, int len)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      This function sends an Erlang term to a process.
        
<P>      <CODE>fd</CODE> is an open descriptor to an Erlang connection.
        
<P>      <CODE>to</CODE> is the Pid of the intended recipient of the
         message.
        
<P>      <CODE>buf</CODE> is the buffer containing the term in binary
         format.
        
<P>      <CODE>len</CODE> is the length of the message in bytes.
        
<P>      The function returns 0 if successful, otherwise -1, in the
         latter case it will set <CODE>erl_errno</CODE> to <CODE>EIO</CODE>.

</DIV>

<P><A NAME="ei_send_tmo/5"><STRONG><CODE>int ei_send_tmo(int fd, erlang_pid* to, char*
buf, int len, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_send with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_send_encoded/4"><STRONG><CODE>int ei_send_encoded(int fd, erlang_pid* to, char* buf, int len)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>Works exactly as ei_send, the alternative name reained for
        backward compatibility. The function will <STRONG>not</STRONG> be
        removed without notice.
</DIV>

<P><A NAME="ei_send_encoded_tmo/5"><STRONG><CODE>int ei_send_encoded_tmo(int fd, erlang_pid* to, char*
buf, int len, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_send_encoded with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_reg_send/5"><STRONG><CODE>int ei_reg_send(ei_cnode* ec, int fd,
        char* server_name, char* buf, int len)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      This function sends an Erlang term to a registered process.

        
<P>      This function sends an Erlang term to a process.
        
<P>      <CODE>fd</CODE> is an open descriptor to an Erlang connection.
        
<P>      <CODE>server_name</CODE> is the registered name of the intended
         recipient.
        
<P>      <CODE>buf</CODE> is the buffer containing the term in binary
         format.
        
<P>      <CODE>len</CODE> is the length of the message in bytes.
        
<P>      The function returns 0 if successful, otherwise -1, in the
         latter case it will set <CODE>erl_errno</CODE> to <CODE>EIO</CODE>.
        
<P>      Example, send the atom &#34;ok&#34; to the process &#34;worker&#34;:
         
<PRE>
ei_x_buff x;
ei_x_new_with_version(&#38;x);
ei_x_encode_atom(&#38;x, &#34;ok&#34;);
if (ei_reg_send(&#38;ec, fd, x.buff, x.index) &#60; 0)
    handle_error();
        
</PRE>

</DIV>

<P><A NAME="ei_reg_send_tmo/6"><STRONG><CODE>int ei_reg_send_tmo(ei_cnode* ec, int fd,
        char* server_name, char* buf, int len, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_reg_send with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_send_reg_encoded/5"><STRONG><CODE>int ei_send_reg_encoded(int fd, const
        erlang_pid *from, const char *to, const char *buf, int len)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>This function is retained for compatibility with code
        generated by the interface compiler and with code following
        examples in the same application.
        
<P>The function works as <CODE>ei_reg_send</CODE> with one
        exception. Instead of taking the <CODE>ei_cnode</CODE> as a first
        argument, it takes a secod argument, an <CODE>erlang_pid</CODE>
        which should be the process identifier of the sending process
        (in the erlang distribution protocol). 
        
<P>A suitable <CODE>erlang_pid</CODE> can be constructed from the
        <CODE>ei_cnode</CODE> structure by the following example code:
        
<PRE>
          ei_cnode ec;
          erlang_pid *self;
          int fd; /* the connection fd */
          ...
          self = ei_self(&#38;ec);
          self-&#62;num = fd;
        
</PRE>

</DIV>

<P><A NAME="ei_send_reg_encoded_tmo/5"><STRONG><CODE>int ei_send_reg_encoded_tmo(int fd, const
        erlang_pid *from, const char *to, const char *buf, int len)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_send_reg_encoded with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_rpc/7"><STRONG><CODE>int ei_rpc(ei_cnode *ec, int fd, char *mod,
        char *fun, const char *argbuf, int argbuflen, ei_x_buff *x)</CODE></STRONG></A><BR>
<A NAME="ei_rpc_to/6"><STRONG><CODE>int ei_rpc_to(ei_cnode *ec, int fd, char *mod,
        char *fun, const char *argbuf, int argbuflen)</CODE></STRONG></A><BR>
<A NAME="ei_rpc_from/5"><STRONG><CODE>int ei_rpc_from(ei_cnode *ec, int fd,
        int timeout, erlang_msg *msg, ei_x_buff *x)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      These functions support calling Erlang functions on remote nodes.
         <CODE>ei_rpc_to()</CODE> sends an rpc request to a remote node and
         <CODE>ei_rpc_from()</CODE> receives the results of such a call.
         <CODE>ei_rpc()</CODE> combines the functionality of these two functions
         by sending an rpc request and waiting for the results. See also
         <CODE>rpc:call/4</CODE>. 
        
<P>      <CODE>ec</CODE> is the C-node structure previously initiated by a
         call to <CODE>ei_connect_init()</CODE> or
         <CODE>ei_connect_xinit()</CODE>
        
<P>      <CODE>fd</CODE> is an open descriptor to an Erlang connection.
        
<P>      <CODE>timeout</CODE> is the maximum time (in ms) to wait for
         results. Specify <CODE>ERL_NO_TIMEOUT</CODE> to wait forever.
         <CODE>ei_rpc()</CODE> will wait infinitely for the answer,
         i.e. the call will never time out.
        
<P>      <CODE>mod</CODE> is the name of the module containing the function
         to be run on the remote node.
        
<P>      <CODE>fun</CODE> is the name of the function to run.
        
<P>      <CODE>argbuf</CODE> is a pointer to a buffer with an encoded
         Erlang list, without a version magic number, containing the
         arguments to be passed to the function.
        
<P>      <CODE>argbuflen</CODE> is the length of the buffer containing the
         encoded Erlang list.
        
<P>      <CODE>msg</CODE> structure of type <CODE>erlang_msg</CODE> and contains
         information on the message received. See <CODE>ei_receive_msg()</CODE>
         for a description of the <CODE>erlang_msg</CODE> format.
        
<P>      <CODE>x</CODE> points to the dynamic buffer that receives the
         result. For for <CODE>ei_rpc()</CODE> this will be the result
         without the version magic number. For <CODE>ei_rpc_from()</CODE>
         the result will return a version magic number and a 2-tuple
         <CODE>{rex,Reply}</CODE>.
        
<P>      <CODE>ei_rpc()</CODE> returns the number of bytes in the result
         on success and -1 on failure. <CODE>ei_rpc_from()</CODE> returns
         number of bytes or one of <CODE>ERL_TICK</CODE>, <CODE>ERL_TIMEOUT</CODE>
         and <CODE>ERL_ERROR</CODE> otherwise. When failing,
         all three functions set <CODE>erl_errno</CODE> to one of:
        
<P>
<DL>

<DT>
<CODE>EIO</CODE>
</DT>

<DD>
I/O error.
</DD>

<DT>
<CODE>ETIMEDOUT</CODE>
</DT>

<DD>
Timeout expired.
</DD>

<DT>
<CODE>EAGAIN</CODE>
</DT>

<DD>
Temporary error: Try again.
</DD>

</DL>

<P>      Example, check to see if an erlang process is alive:
         
<PRE>
int index = 0, is_alive;
ei_x_buff args, result;

ei_x_new(&#38;result);
ei_x_new(&#38;args);
ei_x_encode_list_header(&#38;args, 1);
ei_x_encode_pid(&#38;args, &#38;check_pid);
ei_x_encode_empty_list(&#38;args);

if (ei_rpc(&#38;ec, fd, &#34;erlang&#34;, &#34;is_process_alive&#34;,
           args.buff, args.index, &#38;result) &#60; 0)
    handle_error();

if (ei_decode_version(result.buff, &#38;index) &#60; 0
    || ei_decode_bool(result.buff, &#38;index, &#38;is_alive) &#60; 0)
    handle_error();
        
</PRE>

</DIV>

<P><A NAME="ei_publish/2"><STRONG><CODE>int ei_publish(ei_cnode *ec, int port)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      These functions are used by a server process to register
         with the local name server <STRONG>epmd</STRONG>, thereby allowing
         other processes to send messages by using the registered name.
         Before calling either of these functions, the process should
         have called <CODE>bind()</CODE> and <CODE>listen()</CODE> on an open socket.
        
<P>      <CODE>ec</CODE> is the C-node structure.
        
<P>      <CODE>port</CODE> is the local name to register, and should be the
         same as the port number that was previously bound to the socket.
        
<P>      <CODE>addr</CODE> is the 32-bit IP address of the local host.
        
<P>      To unregister with epmd, simply close the returned
         descriptor. See also <CODE>ei_unpublish()</CODE>.
        
<P>      On success, the functions return a descriptor connecting the
         calling process to epmd. On failure, they return -1 and set
         <CODE>erl_errno</CODE> to <CODE>EIO</CODE>.
        
<P>      Additionally, <CODE>errno</CODE> values from <CODE>socket</CODE><STRONG>(2)</STRONG>
         and <CODE>connect</CODE><STRONG>(2)</STRONG> system calls may be propagated
         into <CODE>erl_errno</CODE>.

</DIV>

<P><A NAME="ei_publish_tmo/3"><STRONG><CODE>int ei_publish_tmo(ei_cnode *ec, int port,
unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_publish with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_accept/3"><STRONG><CODE>int ei_accept(ei_cnode *ec, int listensock,
ErlConnect *conp)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      This function is used by a server process to accept a
         connection from a client process.
        
<P>      <CODE>ec</CODE> is the C-node structure.
        
<P>      <CODE>listensock</CODE> is an open socket descriptor on which
         <CODE>listen()</CODE> has previously been called.
        
<P>      <CODE>conp</CODE> is a pointer to an <CODE>ErlConnect</CODE> struct,
         described as follows:
        
<PRE>
typedef struct {
  char ipadr[4];             
  char nodename[MAXNODELEN];
} ErlConnect;
        
</PRE>

<P>      On success, <CODE>conp</CODE> is filled in with the address and
         node name of the connecting client and a file descriptor is
         returned. On failure, <CODE>ERL_ERROR</CODE> is returned and
         <CODE>erl_errno</CODE> is set to <CODE>EIO</CODE>.

</DIV>

<P><A NAME="ei_accept_tmo/4"><STRONG><CODE>int ei_accept_tmo(ei_cnode *ec, int listensock,
ErlConnect *conp, unsigned timeout_ms)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_accept with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_unpublish/1"><STRONG><CODE>int ei_unpublish(ei_cnode *ec)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      This function can be called by a process to unregister a
         specified node from epmd on the localhost. This may be
         useful, for example, when epmd has not detected the failure of a
         node, and will not allow the name to be reused. If you use this
         function to unregister your own process, be sure to also close
         the descriptor that was returned by <CODE>ei_publish()</CODE>.
        
<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Note!" SRC="note.gif"></TD>
    <TD>

<P>Careless use of this function may have unpredictable
         results, if the registered node is in fact still running.
            </TD>
  </TR>
</TABLE>

<P>      <CODE>ec</CODE> is the node structure of the node to unregister.
        
<P>      If the node was successfully unregistered from epmd, the
         function returns 0. Otherwise, it returns -1 and sets
         <CODE>erl_errno</CODE> is to <CODE>EIO</CODE>.

</DIV>

<P><A NAME="ei_unpublish_tmo/2"><STRONG><CODE>int ei_unpublish_tmo(ei_cnode *ec, unsigned
timeout_ms)
</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      ei_unpublish with an optional timeout argument,
         see the description at the beginning of this document.
        
</DIV>

<P><A NAME="ei_thisnodename/1"><STRONG><CODE>const char *ei_thisnodename(ei_cnode *ec)</CODE></STRONG></A><BR>
<A NAME="ei_thishostname/1"><STRONG><CODE>const char *ei_thishostname(ei_cnode *ec)</CODE></STRONG></A><BR>
<A NAME="ei_thisalivename/1"><STRONG><CODE>const char *ei_thisalivename(ei_cnode *ec)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      These functions can be used to retrieve information about
         the C Node. These values are initially set with
         <CODE>ei_connect_init()</CODE> or <CODE>ei_connect_xinit()</CODE>.
        
<P>      They simply fetches the appropriate field from the <CODE>ec</CODE>
         structure. Read the field directly will probably be safe for
         a long time, so these functions are not really needed.

</DIV>

<P><A NAME="ei_self/1"><STRONG><CODE>erlang_pid *ei_self(ei_cnode *ec)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>      This function retrieves the Pid of the C-node. Every C-node
         has a (pseudo) pid used in <CODE>ei_send_reg</CODE>, <CODE>ei_rpc</CODE>
         and others. This is contained in a field in the <CODE>ec</CODE>
         structure. It will be safe for a long time to fetch this
         field directly from the <CODE>ei_cnode</CODE> structure.

</DIV>

<P><A NAME="*ei_gethostbyname/1"><STRONG><CODE>struct hostent *ei_gethostbyname(const char *name)</CODE></STRONG></A><BR>
<A NAME="*ei_gethostbyaddr/3"><STRONG><CODE>struct hostent *ei_gethostbyaddr(const char *addr, int len, int type)</CODE></STRONG></A><BR>
<A NAME="*ei_gethostbyname_r/5"><STRONG><CODE>struct hostent *ei_gethostbyname_r(const char *name, 
                                 struct hostent *hostp, 
                                 char *buffer, 
                                 int buflen, 
                                 int *h_errnop)</CODE></STRONG></A><BR>
<A NAME="*ei_gethostbyaddr_r/7"><STRONG><CODE>struct hostent *ei_gethostbyaddr_r(const char *addr,
                                 int length, 
                                 int type, 
                                 struct hostent *hostp,
                                 char *buffer, 
                                 int buflen, 
                                 int *h_errnop)</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P> These are convinience functions for some common name lookup functions.

</DIV>

<H3>Debug Information</H3>
<DIV CLASS=REFBODY>

<P> If a connection attempt fails, the following can be checked:

<P>
<UL>

<LI>
<CODE>erl_errno</CODE>
</LI>


<LI>
that the right cookie was used
</LI>


<LI>
that <STRONG>epmd</STRONG> is running
</LI>


<LI>
the remote Erlang node on the other side is running the
        same version of Erlang as the <CODE>ei</CODE>
        library.
</LI>


</UL>

</DIV>

<H3>AUTHORS</H3>
<DIV CLASS=REFBODY>
Jakob Cederlund - support@erlang.ericsson.se<BR>

</DIV>
<CENTER>
<HR>
<SMALL>erl_interface 3.5.5.2<BR>
Copyright &copy; 1991-2006
<A HREF="http://www.erlang.se">Ericsson AB</A><BR>
</SMALL>
</CENTER>
</BODY>
</HTML>