Man Page: rmr_wh_send_msg





#include <rmr/rmr.h>

rmr_mbuf_t* rmr_wh_send_msg( void* vctx, rmr_whid_t id, rmr_mbuf_t* msg )


The rmr_wh_send_msg function accepts a message buffer from the user application and attempts to send it using the wormhole ID provided (id). Unlike rmr_send_msg, this function attempts to send the message directly to a process at the other end of a wormhole which was created with rmr_wh_open(). When sending message via wormholes, the normal RMR routing based on message type is ignored, and the caller may leave the message type unspecified in the message buffer (unless it is needed by the receiving process).

Vctx is the RMR void context pointer that was returned by the rmr_init function. The message buffer (msg) used to send is the same format as used for regular RMR send and reply to sender operations, thus any buffer allocated by these means, or calls to rmr_rcv_msg() can be passed to this function.


The send operations in RMR will retry soft send failures until one of three conditions occurs:

  • The message is sent without error

  • The underlying transport reports a hard failure

  • The maximum number of retry loops has been attempted

A retry loop consists of approximately 1000 send attempts without any intervening calls to sleep() or usleep(). The number of retry loops defaults to 1, thus a maximum of 1000 send attempts is performed before returning to the user application. This value can be set at any point after RMR initialisation using the rmr_set_stimeout() function allowing the user application to completely disable retires (set to 0), or to increase the number of retry loops.

Transport Level Blocking

The underlying transport mechanism used to send messages is configured in non-blocking mode. This means that if a message cannot be sent immediately the transport mechanism will not pause with the assumption that the inability to send will clear quickly (within a few milliseconds). This means that when the retry loop is completely disabled (set to 0), that the failure to accept a message for sending by the underlying mechanisms (software or hardware) will be reported immediately to the user application.

It should be noted that depending on the underlying transport mechanism being used, it is extremely likely that retry conditions will happen during normal operations. These are completely out of RMR’s control, and there is nothing that RMR can do to avoid or mitigate these other than by allowing RMR to retry the send operation, and even then it is possible (e.g., during connection reattempts), that a single retry loop is not enough to guarantee a successful send.


On success, a new message buffer, with an empty payload, is returned for the application to use for the next send. The state in this buffer will reflect the overall send operation state and should be RMR_OK.

If the state in the returned buffer is anything other than RMR_OK, the user application may need to attempt a retransmission of the message, or take other action depending on the setting of errno as described below.

In the event of extreme failure, a nil pointer is returned. In this case the value of errno might be of some use, for documentation, but there will be little that the user application can do other than to move on.


The following values may be passed back in the state field of the returned message buffer.


The wormhole ID passed in was not associated with an open wormhole, or was out of range for a valid ID.


No wormholes exist, further attempt to validate the ID are skipped.


The message buffer pointer did not refer to a valid message.


The header in the message buffer was not valid or corrupted.

The following values may be assigned to errno on failure.


Parameter(s) passed to the function were not valid, or the underlying message processing environment was unable to interpret the message.


The header information in the message buffer was invalid.


No known endpoint for the message could be found.


The underlying transport refused to accept the message because of a size value issue (message was not attempted to be sent).


The message referenced by the message buffer is corrupt (nil pointer or bad internal length).


Internal RMR error; information provided to the message transport environment was not valid.


Sending was not supported by the underlying message transport.


The device is not in a state that can accept the message.


The device is not able to accept a message for sending. The user application should attempt to resend.


The operation was interrupted by delivery of a signal before the message was sent.


The underlying message environment timed out during the send process.


The underlying message environment is in a shutdown state.


The following is a simple example of how the a wormhole is created (rmr_wh_open) and then how rmr_wh_send_msg function is used to send messages. Some error checking is omitted for clarity.

#include <rmr/rmr.h>    // system headers omitted for clarity

int main() {
   rmr_whid_t whid = -1;   // wormhole id for sending
   void* mrc;      //msg router context
        int i;
   rmr_mbuf_t*  sbuf;      // send buffer
   int     count = 0;
   int     norm_msg_size = 1500;  // most msg fit in this size

   mrc = rmr_init( "43086", norm_msg_size, RMRFL_NONE );
   if( mrc == NULL ) {
      fprintf( stderr, "[FAIL] unable to initialise RMR environment\\n" );
      exit( 1 );

   while( ! rmr_ready( mrc ) ) {        // wait for routing table info
      sleep( 1 );

   sbuf = rmr_alloc_msg( mrc, 2048 );

   while( 1 ) {
     if( whid < 0 ) {
       whid = rmr_wh_open( mrc, "localhost:6123" );  // open fails if endpoint refuses conn
          if( RMR_WH_CONNECTED( wh ) ) {
           snprintf( sbuf->payload, 1024, "periodic update from sender: %d", count++ );
           sbuf->len =  strlen( sbuf->payload );
           sbuf = rmr_wh_send_msg( mrc, whid, sbuf );

     sleep( 5 );


rmr_alloc_msg(3), rmr_call(3), rmr_free_msg(3), rmr_init(3), rmr_payload_size(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), rmr_set_stimeout(3), rmr_wh_open(3), rmr_wh_close(3), rmr_wh_state(3)