.if false
==================================================================================
   Copyright (c) 2019-2020 Nokia
   Copyright (c) 2018-2020 AT&T Intellectual Property.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
==================================================================================
.fi

.if false
    Mnemonic    rmr_init_man.xfm
    Abstract    The manual page for the rmr_init function.
    Author      E. Scott Daniels
    Date        28 January 2019
.fi

.gv e LIB lib
.im &{lib}/man/setup.im

&line_len(6i)

&h1(RMR Library Functions)
&h2(NAME)
    rmr_init

&h2(SYNOPSIS)
&indent
&ex_start
#include <rmr/rmr.h>

void* rmr_init( char* proto_port, int max_msg_size, int flags );
&ex_end

&uindent

&h2(DESCRIPTION)
The &cw(rmr_init) function prepares the environment for sending and receiving messages.
It does so by establishing a worker thread (pthread) which subscribes to a route table
generator which provides the necessary routing information for the RMR library to
send messages.

&space
&ital(Port) is used to listen for connection requests from other RMR based applications.
The &ital(max_msg_size) parameter is used to allocate receive buffers and is the
maximum message size which the application expects to receive.
This value is the sum of &bold(both) the maximum payload size &bold(and) the maximum
trace data size.
This value is also used as the default message size when allocating message buffers.
Messages arriving which are longer than the given maximum will be dropped without
notification to the application.
A warning is written to standard error for the first message which is too large on
each connection.

&space
&ital(Flags) allows for selection of some RMr options at the time of initialisation.
These are set by ORing &cw(RMRFL) constants from the RMr header file. Currently the
following flags are supported:

&half_space
&beg_dlist(1i : &bold_font )
&ditem(RMRFL_NONE)
    No flags are set.

&half_space
&ditem(RMRFL_NOTHREAD)
    The route table collector thread is not to be started. This should only be used
    by the route table generator application if it is based on RMr.

&half_space
&ditem(RMRFL_MTCALL)
    Enable multi-threaded call support.

&half_space
&ditem(RMRFL_NOLOCK)
    Some underlying transport providers (e.g. SI95) enable locking to be turned off
    if the user application is single threaded, or otherwise can guarantee that RMR
    functions will not be invoked concurrently from different threads. Turning off
    locking can help make message receipt more efficient.
    If this flag is set when the underlying transport does not support disabling
    locks, it will be ignored.
&end_dlist

&h3(Multi-threaded Calling)
The support for an application to issue a &ital(blocking call) by the &cw(rmr_call()) function
was limited such that only user applications which were operating in a single thread
could safely use the function.
Further, timeouts were message count based and not time unit based.
Multi-threaded call support adds the ability for a user application with multiple threads
to invoke a blocking call function with the guarantee that the correct response message
is delivered to the thread.
The additional support is implemented with the &ital(rmr_mt_call()) and &ital(rmr_mt_rcv())
function calls.
&space

Multi-threaded call support requires the user application to specifically enable it
when RMr is initialised.
This is necessary because a second, dedicated, receiver thread  must be started, and
requires all messages to be examined and queued by this thread.
The additional overhead is minimal, queuing information is all in the RMr message
header, but as an additional process is necessary the user application must "opt in"
to this approach.

&space
&h2(ENVIRONMENT)
As a part of the initialisation process &cw(rmr_init) reads
environment variables to configure itself.
The following variables are used if found.
&half_space

.** the list of environment vars supported
.im &{lib}/man/env_var_list.im

&h2(RETURN VALUE)
The &cw(rmr_init) function returns a void pointer (a contex if you will) that is passed
as the first parameter to nearly all other RMR functions.
If &cw(rmr_init) is unable to properly initialise the environment, NULL is returned and
errno is set to an appropriate value.

&h2(ERRORS)
The following error values are specifically set by this RMR function. In some cases the
error message of a system call is propagated up, and thus this list might be incomplete.

&beg_dlist(.75i : ^&bold_font )
&di(ENOMEM) Unable to allocate memory.
&end_dlist

&h2(EXAMPLE)
&ex_start
   void*  uh;
   rmr_mbuf* buf = NULL;

   uh = rmr_init( "43086", 4096, 0 );
   buf = rmr_rcv_msg( uh, buf );
&ex_end

&h2(SEE ALSO )
.ju off
rmr_alloc_msg(3),
rmr_call(3),
rmr_free_msg(3),
rmr_get_rcvfd(3),
rmr_mt_call(3),
rmr_mt_rcv(3),
rmr_payload_size(3),
rmr_send_msg(3),
rmr_rcv_msg(3),
rmr_rcv_specific(3),
rmr_rts_msg(3),
rmr_ready(3),
rmr_fib(3),
rmr_has_str(3),
rmr_tokenise(3),
rmr_mk_ring(3),
rmr_ring_free(3)
.ju on