2 ==================================================================================
3 Copyright (c) 2019 Nokia
4 Copyright (c) 2018-2019 AT&T Intellectual Property.
6 Licensed under the Apache License, Version 2.0 (the "License");
7 you may not use this file except in compliance with the License.
8 You may obtain a copy of the License at
10 http://www.apache.org/licenses/LICENSE-2.0
12 Unless required by applicable law or agreed to in writing, software
13 distributed under the License is distributed on an "AS IS" BASIS,
14 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 See the License for the specific language governing permissions and
16 limitations under the License.
17 ==================================================================================
22 Mnemonic rmr_mt_call_man.xfm
23 Abstract The manual page for the rmr multi-threaded call function.
24 Author E. Scott Daniels
29 .im &{lib}/man/setup.im
33 &h1(RMR Library Functions)
42 extern rmr_mbuf_t* rmr_mt_call( void* vctx, rmr_mbuf_t* msg, int id, int timeout );
47 The &cw(rmr_mt_call) function sends the user application message to a remote
48 endpoint, and waits for a corresponding response message before returning
49 control to the user application.
50 The user application supplies a completed message buffer, as it would for
51 a &cw(rmr_send_msg) call, but unlike with a send, the buffer returned will have
52 the response from the application that received the message.
53 The thread invoking the &ital(rmr_mt_call()) will block until a message arrives
54 or until &ital(timeout) milliseconds has passed; which ever comes first.
55 Using a timeout value of zero (0) will cause the thread to block without a timeout.
58 The &ital(id) supplied as the third parameter is an integer in the range of 2 through
60 This is a caller defined "thread number" and is used to match the response message
61 with the correct user application thread.
62 If the ID value is not in the proper range, the attempt to make the call will fail.
65 Messages which are received while waiting for the response are queued on a &ital(normal)
66 receive queue and will be delivered to the user application with the next invocation
67 of &ital(rmr_mt_rcv()) or &ital(rmr_rvv_msg().)
68 by RMR, and are returned to the user application when &cw(rmr_rcv_msg) is
70 These messages are returned in th order received, one per call to &cw(rmr_rcv_msg.)
73 NOTE: Currently the multi-threaded functions are supported only when the NNG
74 transport mechanism is being used. It will not be possible to link a programme
75 using the Nanomsg version of the library when references to this function are
78 &h3(The Transaction ID)
79 The user application is responsible for setting the value of the transaction ID field
80 before invoking &ital(rmr_mt_call.)
81 The transaction ID is a &cw(RMR_MAX_XID) byte field that is used to match the
82 response message when it arrives.
83 RMr will compare &bold(all) of the bytes in the field, so the caller must ensure
84 that they are set correctly to avoid missing the response message.
85 (The application which returns the response message is also expected to ensure that
86 the return buffer has the matching transaction ID. This can be done transparently if
87 the application uses the &ital(rmr_rts_msg()) function and does not adjust the
90 .** pull in common retry text
91 .im &{lib}/man/retry.im
94 The &cw(rmr_mt_call) function returns a pointer to a message buffer with the state set to reflect
95 the overall state of call processing.
96 If the state is &cw(RMR_OK) then the buffer contains the response message; otherwise
97 the state indicates the error encountered while attempting to send the message.
100 If no response message is received when the timeout period has expired, a nil pointer
101 will be returned (NULL).
104 These values are reflected in the state field of the returned message.
107 &beg_dlist(.75i : ^&bold_font )
108 &di(RMR_OK) The call was successful and the message buffer references the response message.
111 &di(RMR_ERR_BADARG) An argument passed to the function was invalid.
114 &di(RMR_ERR_CALLFAILED) The call failed and the value of &ital(errno,) as described below,
115 should be checked for the specific reason.
118 &di(RMR_ERR_NOENDPT) An endpoint associated with the message type could not be found in the
122 &di(RMR_ERR_RETRY) The underlying transport mechanism was unable to accept the message
123 for sending. The user application can retry the call operation if appropriate to
129 The global "variable" &ital(errno) will be set to one of the following values if the
130 overall call processing was not successful.
133 &beg_dlist(.75i : ^&bold_font )
134 &di(ETIMEDOUT) Too many messages were queued before receiving the expected response
137 &di(ENOBUFS) The queued message ring is full, messages were dropped
140 &di(EINVAL) A parameter was not valid
143 &di(EAGAIN) The underlying message system wsa interrupted or the device was busy;
144 the message was &bold(not) sent, and user application should call
145 this function with the message again.
149 The following code bit shows one way of using the &cw(rmr_mt_call) function, and illustrates
150 how the transaction ID must be set.
154 int retries_left = 5; // max retries on dev not available
155 static rmr_mbuf_t* mbuf = NULL; // response msg
156 msg_t* pm; // private message (payload)
158 // get a send buffer and reference the payload
159 mbuf = rmr_alloc_msg( mr, RMR_MAX_RCV_BYTES );
160 pm = (msg_t*) mbuf->payload;
162 // generate an xaction ID and fill in payload with data and msg type
163 rmr_bytes2xact( mbuf, xid, RMR_MAX_XID );
164 snprintf( pm->req, sizeof( pm->req ), "{ \"req\": \"num users\"}" );
165 mbuf->mtype = MT_USR_RESP;
167 msg = rmr_mt_call( mr, msg, my_id, 100 ); // wait up to 100ms
168 if( ! msg ) { // probably a timeout and no msg received
169 return NULL; // let errno trickle up
172 if( mbuf->state != RMR_OK ) {
173 while( retries_left-- > 0 && // loop as long as eagain
174 mbuf->state == RMR_ERR_RETRY &&
175 (msg = rmr_mt_call( mr, msg )) != NULL &&
176 mbuf->state != RMR_OK ) {
178 usleep( retry_delay );
181 if( mbuf == NULL || mbuf->state != RMR_OK ) {
182 rmr_free_msg( mbuf ); // safe if nil
187 // do something with mbuf