HP 800 ACSE/Presentation and ROSE Interface Programmer's Guide - Page 59

Multiple Connections Scenario

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Figure 4-1 Programming Guide 5. Managing Multiple Connections packets and is waiting for the release indication (A_RELEASE_IND) while endpoint D is in AP_IDLE state waiting for the connection indication (A_ASSOC_IND). Multiple Connections Scenario Initiator Process Responder Process servicing servicing Conn B .sent A_ASSOC_REQ .waiting for A_ASSOC_CNF Conn A .sent all data packets .waiting for its turn to receive its last data packet before it sends A_RELEASE_REQ Conn C .sent all data packets .waiting for A_RELEASE_IND Conn D .in IDLE state .waiting for A_ASSOC_IND • If the connections are using synchronous mode, a deadlock situation occurs. Endpoint A is blocked until endpoint B receives a A_ASSOC_CNF which will never happen, because the remote process is servicing endpoint C which is waiting for A_RELEASE_REQ sent by endpoint A and endpoint A is blocked. • On the other hand, using asynchronous mode, ap_rcv() will return AP_AGAIN on communication endpoint B because there is no data to process. It would not block the process, and the application can continue to service the next connection. Communication endpoint A would then be able to receive its last data packet and send a release request (A_RELEASE_REQ) to endpoint C. Then C would be able to process its release indication (A_RELEASE_IND) and reply (A_RELEASE_RSP). Endpoint D would receive its connection indication (A_ASSOC_IND) and so on. For more information on how an application can handle synchronous and asynchronous mode processing, see the section "Using Synchronous vs. Asynchronous Mode.". Chapter 4 59

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Chapter 4
59
Programming Guide
5. Managing Multiple Connections
packets and is waiting for the release indication (A_RELEASE_IND)
while endpoint D is in AP_IDLE state waiting for the connection
indication (A_ASSOC_IND).
Figure 4-1
Multiple Connections Scenario
•
If the connections are using synchronous mode, a deadlock situation
occurs. Endpoint A is blocked until endpoint B receives a
A_ASSOC_CNF which will never happen, because the remote process
is servicing endpoint C which is waiting for A_RELEASE_REQ sent
by endpoint A and endpoint A is blocked.
•
On the other hand, using asynchronous mode, ap_rcv() will return
AP_AGAIN on communication endpoint B because there is no data to
process. It would not block the process, and the application can
continue to service the next connection. Communication endpoint A
would then be able to receive its last data packet and send a release
request (A_RELEASE_REQ) to endpoint C. Then C would be able to
process its release indication (A_RELEASE_IND) and reply
(A_RELEASE_RSP). Endpoint D would receive its connection
indication (A_ASSOC_IND) and so on.
For more information on how an application can handle synchronous and
asynchronous mode processing, see the section “Using Synchronous vs.
Asynchronous Mode.”.
Initiator Process
Responder Process
====================================================
servicing
servicing
Conn B
Conn C
.sent A_ASSOC_REQ
.waiting for
A_ASSOC_CNF
.sent all data packets
.waiting for
A_RELEASE_IND
Conn A
.sent all data packets
.waiting for its turn
to receive its last
data packet before
it sends A_RELEASE_REQ
Conn D
.in IDLE state
.waiting for
A_ASSOC_IND