HP 3000 Port Structure User Manual

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HP 3000 APPLICATION NOTE # 91
Using The Port Structure
Under MPE/XL
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Г’ HEWLETT October 01, 1991
- PACKARD Document P/N 5960-6659
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HP 3000 Application Note # 91
USING THE PORT STRUCTURE UNDER MPE/XL
Introduction
Ever since it was created, the MPE/XL operating system has always used a specific concept to
support the transmission of data between the processes and the process synchronization of the
operating system itself.
This concept is known as the PORT FACILITY.
The purpose of this Application Note is to give a general outline of this new system
functionality as the MPE/XL release 2.1, in conjunction with the Architected Interface, now
allows the users to access these structures.
The following considerations shall be discussed hereunder:
What is a PORT? How are the PORTs used? What is a SUBQUEUE? What is a PORT
SERVER? What are the advantages of using the Architected Interface in connection with the
PORTs? |
WHAT 1S A PORT?
A port is a data structure dedicated to the reception of messages. Under MPE/XL, the only
possibility for a system process A to communicate with a system process B consists in the
former sending a message to the PORT and process B going to read it on the said PORT.
If needed, process B may come and wait on this PORT until a message comes in, in which
case it remains in “standby” state. The incoming message from process A will “awake” B
which immediately reads the message made available on the PORT.
For those users accustomed to MPE/V, this inter-process communication feature was formerly
supported by the “eXtra-Data Segments”, and intrinsics SENDMAIL, RECEIVEMAIL. Note
that these concepts are maintained under MPE/XL, albeit only in compatible mode.
In this paper, the following structure will be used to represent a PORT:
HP 3000 Application Note # 91 1
| | PORT
There are three different types of PORTS:
1. MESSAGE PORT:s: the most widely used, for they allow “plain” inter-process message
transmission. In other words, a message may consist of a set of characters in a format that
can be understood both by the “writer” and the “reader” processes.
2. SIGNAL PORTs: these have the same characteristics as the above Message Ports except
that the message size is cut to zero byte. Use of the SIGNAL PORT, therefore, will be
confined to event triggering and inter-process synchronization.
3. SEMAPHORE PORT:s: in many ways similar to the SIGNAL PORTS, they were used in
the initial versions of MPE/XL. They have now been totally abandoned for the SIGNAL
PORTS.
Before we go any further, let us study briefly a concrete example of how a PORT is used by
MPE/XL.
A user process is running a FREAD on a file which internally results in this process writing
a message onto a PORT of the IO system module. The message will contain information to
answer the following questions: Where exactly on the disk should you read from? What
length of disk should be read? In what area of the memory should the data read be stored?
Once these questions have been sent to the IO system, the user process issues a message
reception request on a PORT called IO-COMPLETION PORT.
As can be assumed from its name, this is the port to which the IO module is going to write its
message. This message will contain the IO report. The user process then reads the message,
and if the report shows that the IO has been successful, the process may continue to run.
This very simple example summarizes the various functions of the PORTs: data transfers
between the processes and process synchronization.
HOW ARE THE PORTs USED?
When a message is sent to a port, it is stored there in a chained FIFO (First-In First-Out)-
type list. This means the messages will be read by the process waiting for reception on this
PORT, in their order of arrival. Therefore, it is possible to have several messages waiting to
be processed on a given PORT. 5
A process, however, can send only one message at a time to a PORT.
If several messages are to be sent, the process must invoke the sending procedure as many
times as required.
Up to now, we have examined the PORT as a global concept. Let us now turn to the notion
of SUBQUEUE.
2 HP 3000 Application Note # 91
| 0 WHAT IS À SUBQUEUE?
Each PORT is divided into a set of SUBQUEUES (up to 32 per PORT), which actually
represent the various chained lists that are attached to a given PORT. :
So, this SUBQUEUE concept will be used to assign priorities to the messages queued on this
PORT, with SUBQUEUE 0 always having a higher priority than SUBQUEUE 31.
When a message is to be sent to a PORT, the process may do so without specifying the
SUBQUEUE, in which case it defaults to SUBQUEUE 0. However, it may also choose to
specify a specific SUBQUEUE.
On another hand, a process may wait globally on a PORT, that is it will receive the first
message of the highest priority SUBQUEUE. A process may also wait on a given SUBQUEUE
of a specific PORT. | |
Last of all, a SUBQUEUE may be either in ENABLE or DISABLE mode. If it is ENABLEd,
it is possible to read the messages reaching this PORT, but if it is DISABLE, the messages
received on this SUBQUEUE cannot be read, unless the relevant SUBQUEUE number is
specified. |
Example:
This typical example should help you better understand the concepts of SUBQUEUE,
ENABLE, and DISABLE.
Assume a PORT with three SUBQUEUES (0, 1, 2), where SUBQUEUES 0 and 2 are
ENABLEd, and SUBQUEUE 1 is DISABLEd. A number of messages are sent to this port
on different SUBQUEUES, as shown in the diagram below. Each message here contains the
sending order number on this PORT. So we shall issue a number of reception requests to
clearly understand in what order the messages are read.
Mes n° 7 ---> Mes”n 4 --->. SubQ O ENA
Mes n°5 --->Mes n° 2 ---> Mes”n 1 ---> SubQ 1 DIS PORT
Mes n° 6 ---> Mes°n 3 ---> SubQ 2 ENA
Figure 1-1.
HP 3000 Application Note # 91 3
Request No.1: read without specifying a SUBQUEUE ==> Mess 4. In this case, a message is
received from the highest priority ENABLEd SUBQUEUE (0 here).
Request No.2: read SUBQUEUE No. 1 ==> Mess 1. Although it is DISABLEd (this may
— be assumed from the fact that the SUBQUEUE for reception has been specified), the first
; ‘ message present on SUBQUEUE 1 is received.
Request No.3: read from SUBQUEUE No. 0 ==> Mess 7. No comments ... (Message 4 has
already been read) |
Request No.4: read without specifying any SUBQUEUE ==> Mess 3. There is no message
left in SUBQUEUE 0, SUBQUEUE 1 is DISABLE, the first message available on the next
SUBQUEUE in terms of priority ranking is No.3.
After the concepts of PORT, SUBQUEUE, priority in the SUBQUEUES, we shall now turn to
the concept of PORT SERVER.
WHAT IS A PORT SERVER?
A SERVER is a specific section of code which knows where to read and how to process a
message on a given PORT. Thus, the function of the PORT is both to store the messages, and
also to invoke the SERVER as soon as a message has arrived.
It is mandatory that a SERVER should be non re-entrant, in other words, if a message has
just been received on a PORT, the SERVER will run. If, while it is executing, the SERVER
is interrupted by the DISPATCHER (pre-emption or timesliced), and another message is
received on the PORT, the SERVER is not invoked again. This provides for consistency with
the above- described notion of message priority. On completing processing of a message,
however, a SERVER is immediately re-invoked if a message has arrived while the former
message was being processed, and so on until the PORT is empty.
The various types of SERVERs are described below:
PROCEDURE SERVER: in this case, the SERVER is a procedure to be run on the stack
of the write process. The advantage of this procedure is that running it does not require
loading any specific process. This i is why this SERVER is particularly effective in terms of
performance.
PROCESS SERVER: here the SERVER is a process with its whole operating environment,
that is the stack, code and system structures required for its execution. The drawback of the
SERVER procedures is that when you start them up, you have to switch contexts, which
involves substantial overhead.
The PROCESS SERVER of a PORT i is defined at PORT creation, that is as an intrinsic
feature of this PORT.
ANY PROCESS SERVER: the characteristic of a PORT defined with ANY PROCESS
SERVER is that it may be served by any process which has made a message reception request.
In this case, a unique process may wait on a PORT. If a second process attempts to wait on
the same PORT, an error is returned.
4 HP 3000 Application Note # 91
WHAT ARE THE ADVANTAGES OF USING THE ARCHITECTIED INTERFACE IN
CONNECTION WITH THE PORTS?
After reviewing the concept of PORT, let us now discuss the contribution of the
ARCHITECTED INTERFACE (available for MPE/XL 2.1).
The Architected Interface allows you to integrate the PORT concept in your programs with all
the related facilities offered in terms of process synchronization. This interface allows you to
use all the above functions with the exception of the PROCEDURE SERVER.
Four procedures are available:
AIFPORTOPEN: creates a PORT, if it does not exist yet, or opens it if it already exists (like
a file, a PORT must be open to be used). A PORT gets a name at creation time, this name
should be used for all references to the PORT. The PORT access is protected by a password.
AIFPORTCLOSE: closes a PORT, or deletes it.
AIFPORTSEND: this procedure is used to send a message to a PORT. The maximum length
of the message is 256 bytes.
When writing a message to a PORT, its priority must be defined; in fact, this priority matches
the priority of the SUBQUEUE to which it belongs.
Moreover, when the user is sending a message, he is allowed to specify a TIMEOUT in
number of seconds. If different from Zero (unlimited wait), this timeout is equal to the time
a message remains on a PORT before it is deleted if no process has come to read it. If the
TIMEOUT is greater than or equal to 0, the write process is locked in until this message
is read or deleted. Otherwise, if the TIMEOUT is negative, the message is written in
NONWAIT mode, that is the write process is not locked in until the message has been read or
deleted.
AIFPORTRECEIVE: this procedure allows reading a message and setting a process to waiting
for reception on a PORT. A TIMEOUT may be set for the waiting, a PRIORITY_MASK
which actually defines the ENABLE/DISABLE SUBQUEUES.
CONCLUSION
Message transmission, process synchronization, task priority management ... all of these new
functions can now be used by your programs in NATIVE mode from the moment you acquire
the Architected Interface.
HP 3000 Application Note # 91 5
Published Application Notes
HP 3000
Following is a list of the Application Notes published to date. If you would like to order single
copies of back issues please use the Request Form attached and indicate the number(s) of the
note(s) you need, and the part number(s).
Note # | Part Number Topic
1 5958-5824 | Printer Configuration Guide - Version 1
2 5960-2841 | Terminal types for HP 3000 HPIB Computers - Version 1
3 5960-2842 |Plotter Configuration Guide
4 5960-2843 | Printer Configuration Guide - Version 2 e e
5 5960-2844 | MPE System Logfile Record Formats
6 5960-2845 [Stack Operation
7 5960-2846 | COBOL II/3000 Programs: Tracing Illegal Data
8 5960-2847 | KSAM Topics: COBOL’s Index 1/0: File Data Integrity -
9 5960-2848 | Port Failures, Terminal Hangs, TERM DSM
10 5960-2849 | Serial Printers - Configuration, Cabling, Muxes |
11 5960-2850 | System Configuration or System Table Related Errors
12 5960-2851 | Pascal 3000 - Using Dynamic Variables |
13 5960-2852 | Terminal Types for HP 3000 HPIB Computers - Version 2
14 5960-2853 | Laser Printers - A Software and Hardware Overview -
15 5960-2854 | FORTRAN Language Considerations - A Guide to Common Problems
16 5960-2855 |IMAGE: Updating to TurboIMAGE & Improving Database Loads
17 5960-2856 | Optimizing VPLUS Utilization |
18 5960-2857 | The Case of the Suspect Track for 792X Disc Drives
19 5960-2858 |Stack Overflows: Causes & Cures for COBOL II Programs
20 5960-2859 | Output Spooling |
21 5960-2860 | COBOLII and MPE Intrinsics
22 5960-2861 | Asynchronous Modems
Published Application Notes 1
HP 3000 (continued)
Note # | Part Number Topic
23 | 5960-2862 | VFC Files
24 5960-2863 | Private Volumes
‚25 | 5960-2864 |TurboIMAGE: Transaction Logging
26 | 5960-2865 |HP 2680A, 2688A Error Trailers
27 | 5960-2866 |HP Trend: An Installation and Problem Solving Guide
28 5960-2867 | The Startup State Configurator .
29 | 5960-2868 |A Programmer's Guide to VPLUS 3000
30 5960-2869 | Disc Cache |
31 | 5960-2870 |Calling the CREATEPROCESS Intrinsic
32 | 5960-2871 [Configuring Terminal Buffers
33 : 5960-2872 | Printer Configuration Guide - Version 3
34k] 5880-2873 |RIN Management (Using COBOLII Examples) (A)
34 = 5960-2874 Process Handling (Using COBOLII Examples) (B)
35 | 5960-2875 |HPDESK IV (Script files, FSC, and Installation Considerations)
340 | 5960-2876 |Extra Data Segments (Using COBOLII Examples) (C)
36 | 5960-2877 |Tips for the DESK IV Administrators
37 5960-2878 | AUTOINST: Trouble-free Updates
38 5960-2879 | Store/Restore Errors |
39 5060-2880 |MRJE Emulates a HASP Workstation
40 | 5960-2881 |HP 250 / 260 to HP 3000 Communications Guidelines
41 | 5960-2882 |MPE File Label Revealed
42. | 5960-2883 |System Interrupts
43 5960-2884 | Run Time Aborts
44 5960-2885 | HPPA Patching Conventions for HP3000 900 Series Processors - Version 1
45 | 5960-2886 |Vplus 4 Multiplexers
46 | 5960-2887 |Setting Up an HPDesk HPTelex for the First Time
47 5960-2900 | Customizing Database Data Items & Changing Passwords in JCL Files
-48 | 5959-9215 [Printer Configuration - Version 4
49 | 5959-9227 |Configuring DATACOMM Products Into MPE
: 50 5959-9228 | VFC's for Serial Printers
à Published Application Notes
HP 3000 (continued)
Note | Part Number Topic
#
51. 5959-9237 | Terminal Types for the HP 3000 HPIB Computers
52 5959-9242 | Configuring MRJE
53 | 5959-9245 | Using Special Characters on the 700/9x Series Terminals
54 5959-9251 | Improving Database Performance
5 5959-9258 | Customized Message Catalogs and Help Facilities
56 | 5959-9266 |BRW Tips for Beginners
57 5959-9270 | Configuring the HP 2334 A Plus & HP 2335A As a Statistical Multiplexer
58 5959-9274 | HPPA Pathing Conventions for HP3000 900 Series Processors - Version 2
59 5959-9289 | HP 2334A and HP 2334A Configuration Recipes
60 5959-9301 | TurboIMAGE’s I-FILES and J-FILES
61 5959-7385 | HPDeskManager - Looking Behind the Scenes
62 5959-7803 | Setting Up a System Dictionary
63 5959-7834 | Configuring Telesupport Modems for MPE V/E Systems
64 5960-1816 | Finding Solutions in HP SupportLine
65 5960-1817 | Using the Electronic Call Feature of HP SupportLine
66 5960-1818 | Using the Feedback Feature of HP SupportLine
67 5960-1819 | Printing Documents from HP SupportLine
68 5960-1820 | HP SupportLine Commands
69 5960-2901 | Nonsystem Volume Sets and the Migration of Private Volumes to an
S9000 HP 3000
70 5960-2907 | Modem Links for Remote Console and Standard D'TC Connection s on
Commercial XL HPPA Systems |
71 5960-2918 | Asynchronous Cabling
72 5960-2919 |BRW Tips and Tricks
73 5960-2998 |SNA NRJE Configuration
74 5960-2999 [SNA IMF Configuration
75 5060-3000 | XL NRIJE Configuration
Published Application Notes 3
HP 3000 (continued) (continued)
Note | Part Number Topic
#
76 | 5960-4301 |XL IMF Configuration
77 | 5960-4302 | Calling the BRW Intrinsics
78 | 5960-4303 |PUB.SYS What Is Behind It?
79 5960-4625 | Conquest of Dise Space |
80 5960-4633 | Looking Behind the Scenes of Resource Sharing
81 5960-4637 |MPE/XL System Interrupt Recovery Procedures
82 5960-4347 | Private Volumes
83 | 5060-4396 |Serial Printer Configuration
84 | 5960-4334 |How to Migrate FORTRAN Programs to Newer Compilers and XL
Hardware | |
85 5960-4335 | The Optimization of Programs in MPE/XL
86 5960-4643 |IBM Labeled Tapes Questions and Answers |
87 5960-4666 |Image Logging for HP Financial Accounting Databases
88 5960-4672 | Native Mode Spooler Questions and Answers
89 | 5960-4673 |AUTOINST/XL Questions and Answers
90 | 5960-4701 [The New Spooler
91 | 5960-6659 | Using the Port Structure Under MPE/XL
4 Published Application Notes
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