REQUEST_TO_SEND

The REQUEST_TO_SEND verb notifies the partner TP that the local TP wants to send data.

For the Windows version 3.x system, it is recommended that you use WinAsyncAPPC rather than the blocking version of this call.

The following structure describes the verb control block used by the REQUEST_TO_SEND verb.

struct request_to_send {
    unsigned short      opcode;
    unsigned char       opext;
    unsigned char       reserv2;
    unsigned short      primary_rc;
    unsigned long       secondary_rc;
    unsigned char       tp_id[8];
    unsigned long       conv_id;
};

Members

opcode
Supplied parameter. Specifies the verb operation code, AP_B_REQUEST_TO_SEND.
opext
Supplied parameter. Specifies the verb operation extension, AP_BASIC_CONVERSATION.
primary_rc
Returned parameter. Specifies the primary return code set by APPC at the completion of the verb. The valid return codes vary depending on the APPC verb issued. See Return Codes for valid error codes for this verb.
secondary_rc
Returned parameter. Specifies the secondary return code set by APPC at the completion of the verb. The valid return codes vary depending on the APPC verb issued. See Return Codes for valid error codes for this verb.
tp_id
Supplied parameter. Identifies the local TP.

The value of this parameter is returned by TP_STARTED in the invoking TP or by RECEIVE_ALLOCATE in the invoked TP.

conv_id
Supplied parameter. Provides the conversation identifier.

The value of this parameter is returned by ALLOCATE in the invoking TP or by RECEIVE_ALLOCATE in the invoked TP.

Return Codes

ap_ok
Primary return code; the verb executed successfully.
ap_parameter_check
Primary return code; the verb did not execute because of a parameter error.
ap_bad_conv_id
Secondary return code; the value of conv_id did not match a conversation identifier assigned by APPC.
ap_bad_tp_id
Secondary return code; the value of tp_id did not match a TP identifier assigned by APPC.
ap_state_check
Primary return code; the verb did not execute because it was issued in an invalid state.
ap_r_t_s_bad_state
Secondary return code; the conversation is not in an allowed state when the TP issued this verb.
ap_comm_subsystem_abended
Primary return code; indicates one of the following conditions:

The system administrator should examine the error log to determine the reason for the ABEND.

ap_comm_subsystem_not_loaded
Primary return code; a required component could not be loaded or has terminated while processing the verb. Thus, communication could not take place. Contact the system administrator for corrective action.

When this return code is used with ALLOCATE, it may indicate that no communications subsystem could be found to support the local LU. (For example, the local LU alias specified with TP_STARTED is incorrect or has not been configured.) Note that if lu_alias or mode_name is fewer than eight characters, you must ensure that these fields are filled with spaces to the right. This error is returned if these parameters are not filled with spaces, since there is no node available that can satisfy the ALLOCATE request.

When ALLOCATE produces this return code for a Microsoft® SNA Server Client system configured with multiple nodes, there are two secondary return codes as follows:

0xf0000001
Secondary return code; no nodes have been started.
0xf0000002
Secondary return code; at least one node has been started, but the local LU (when TP_STARTED is issued) is not configured on any active nodes. The problem could be either of the following:
·    The node with the local LU is not started.
·    The local LU is not configured.

ap_conversation_type_mixed
Primary return code; the TP has issued both basic and mapped conversation verbs. Only one type can be issued in a single conversation.
ap_invalid_verb_segment
Primary return code; the VCB extended beyond the end of the data segment.
ap_stack_too_small
Primary return code; the stack size of the application is too small to execute the verb. Increase the stack size of your application.
ap_conv_busy
Primary return code; there can only be one outstanding conversation verb at a time on any conversation. This can occur if the local TP has multiple threads, and more than one thread is issuing APPC calls using the same conv_id.
ap_thread_blocking
Primary return code; the calling thread is already in a blocking call.
ap_unexpected_dos_error
Primary return code; the operating system has returned an error to APPC while processing an APPC call from the local TP. The operating system return code is returned through the secondary_rc. It appears in Intel byte-swapped order. If the problem persists, consult the system administrator.

Remarks

The conversation can be in any of the following states when the TP issues this verb:

CONFIRM

PENDING_POST (OS/2)

RECEIVE

There is no state change.

The request-to-send notification is received by the partner program through the rts_rcvd parameter of the following verbs:

It is also indicated by a primary_rc of ap_ok on TEST_RTS.

Request-to-send notification is sent to the partner TP immediately; APPC does not wait until the send buffer fills up or is flushed. Consequently, the request-to-send notification may arrive out of sequence. For example, if the local TP is in SEND state and issues PREPARE_TO_RECEIVE followed by REQUEST_TO_SEND, the partner TP, in RECEIVE state, may receive the request-to-send notification before it receives the send notification. For this reason, request-to-send can be reported to a TP through a receive verb.

In response to this request, the partner TP can change the conversation to:

The partner TP can also ignore the request-to-send.

The conversation state changes to SEND for the local TP when the local TP receives one of the following values through the what_rcvd parameter of a subsequent receive verb:

The receive verbs are RECEIVE_AND_POST (Windows NT, Windows 95, and OS/2 operating systems), RECEIVE_IMMEDIATE, and RECEIVE_AND_WAIT.