GAP (scscp) - Chapter 9: Service functions

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9 Service functions
9.1 Pinging SCSCP servers
9.1-1 PingSCSCPservice
9.1-2 PingStatistic
9.2 Info classes for SCSCP
9.2-1 InfoSCSCP
9.2-2 InfoMasterWorker
9.3 Other SCSCP Utilities
9.3-1 DateISO8601
9.3-2 CurrentTimestamp
9.3-3 Hostname
9.3-4 MemoryUsageByGAPinKbytes
9.3-5 LastReceivedCallID
9.3-6 IO_PickleToString
9.3-7 IO_UnpickleFromString

### 9 Service functions

#### 9.1 Pinging SCSCP servers

##### 9.1-1 PingSCSCPservice

`‣ PingSCSCPservice`( hostname, portnumber ) | ( function )

Returns: `true` or `fail`

This function returns `true` if the client can establish connection with the SCSCP server at hostname:portnumber. Otherwise, it returns `fail`.

    gap> PingSCSCPservice("localhost",26133);
    true
    gap> PingSCSCPservice("localhost",26140);
    Error: rec(
      message := "Connection refused",
      number := 61 )
    fail

##### 9.1-2 PingStatistic

`‣ PingStatistic`( hostname, portnumber, n ) | ( function )

Returns: nothing

The function is similar to the UNIX `ping`. It tries n times to establish connection with the SCSCP server at hostname:portnumber, and then displays statistical information.

    gap> PingStatistic("localhost",26133,1000);
    1000 packets transmitted, 1000 received, 0% packet loss, time 208ms
    min/avg/max = [ 0, 26/125, 6 ]

#### 9.2 Info classes for SCSCP

##### 9.2-1 InfoSCSCP

`‣ InfoSCSCP` | ( info class )

`InfoSCSCP` is a special Info class for the SCSCP package. The amount of information to be displayed can be specified by the user by setting InfoLevel for this class from 0 to 4, and the default value of InfoLevel for the package is specified in the file `scscp/config.g`. The higher the level is, the more information will be displayed. To change the InfoLevel to `k`, use the command `SetInfoLevel(InfoSCSCP, k)`. In the following examples we demonstrate various degrees of output details using Info messages.

Default Info level:

    gap> SetInfoLevel(InfoSCSCP,2);
    gap> EvaluateBySCSCP( "WS_Factorial",[10],"localhost",26133);
    #I  Creating a socket ...
    #I  Connecting to a remote socket via TCP/IP ...
    #I  Got connection initiation message
    #I  <?scscp service_name="GAP" service_version="4.dev" service_id="localhost:2\
    6133:286" scscp_versions="1.0 1.1 1.2 1.3" ?>
    #I  Requesting version 1.3 from the server ...
    #I  Server confirmed version 1.3 to the client ...
    #I  Request sent ...
    #I  Waiting for reply ...
    #I  <?scscp start ?>
    #I  <?scscp end ?>
    #I  Got back: object 3628800 with attributes
    [ [ "call_id", "localhost:26133:286:JL6KRQeh" ] ]
    rec( attributes := [ [ "call_id", "localhost:26133:286:JL6KRQeh" ] ],
      object := 3628800 )

Minimal Info level:

    gap> SetInfoLevel(InfoSCSCP,0);
    gap> EvaluateBySCSCP( "WS_Factorial",[10],"localhost",26133);
    rec( attributes := [ [ "call_id", "localhost:26133:286:jzjsp6th" ] ],
      object := 3628800 )

Verbose Info level:

    gap> SetInfoLevel(InfoSCSCP,3);
    gap> EvaluateBySCSCP( "WS_Factorial",[10],"localhost",26133);
    #I  Creating a socket ...
    #I  Connecting to a remote socket via TCP/IP ...
    #I  Got connection initiation message
    #I  <?scscp service_name="GAP" service_version="4.dev" service_id="localhost:2\
    6133:286" scscp_versions="1.0 1.1 1.2 1.3" ?>
    #I  Requesting version 1.3 from the server ...
    #I  Server confirmed version 1.3 to the client ...
    #I  Composing procedure_call message:
    <?scscp start ?>
    <OMOBJ xmlns="http://www.openmath.org/OpenMath" version="2.0">
    	<OMATTR>
    		<OMATP>
    			<OMS cd="scscp1" name="call_id"/>
    			<OMSTR>localhost:26133:286:Jok6cQAf</OMSTR>
    			<OMS cd="scscp1" name="option_return_object"/>
    			<OMSTR></OMSTR>
    		</OMATP>
    		<OMA>
    			<OMS cd="scscp1" name="procedure_call"/>
    			<OMA>
    				<OMS cd="scscp_transient_1" name="WS_Factorial"/>
    				<OMI>10</OMI>
    			</OMA>
    		</OMA>
    	</OMATTR>
    </OMOBJ>
    <?scscp end ?>
    #I  Total length 396 characters
    #I  Request sent ...
    #I  Waiting for reply ...
    #I  <?scscp start ?>
    #I Received message:
    <OMOBJ xmlns="http://www.openmath.org/OpenMath" version="2.0">
    	<OMATTR>
    		<OMATP>
    			<OMS cd="scscp1" name="call_id"/>
    			<OMSTR>localhost:26133:286:Jok6cQAf</OMSTR>
    		</OMATP>
    		<OMA>
    			<OMS cd="scscp1" name="procedure_completed"/>
    			<OMI>3628800</OMI>
    		</OMA>
    	</OMATTR>
    </OMOBJ>
    #I  <?scscp end ?>
    #I  Got back: object 3628800 with attributes
    [ [ "call_id", "localhost:26133:286:Jok6cQAf" ] ]
    rec( attributes := [ [ "call_id", "localhost:26133:286:Jok6cQAf" ] ],
      object := 3628800 )
    gap> SetInfoLevel(InfoSCSCP,0);

##### 9.2-2 InfoMasterWorker

`‣ InfoMasterWorker` | ( info class )

`InfoMasterWorker` is a special Info class for the Master-Worker skeleton `ParListWithSCSCP` (8.2-1). The amount of information to be displayed can be specified by the user by setting InfoLevel for this class from 0 to 5, and the default value of InfoLevel for the package is specified in the file `scscp/config.g`. The higher the level is, the more information will be displayed. To change the InfoLevel to `k`, use the command `SetInfoLevel(InfoMasterWorker, k)`. In the following examples we demonstrate various degrees of output details using Info messages.

Default Info level:

    gap> SetInfoLevel(InfoMasterWorker,2);
    gap> ParListWithSCSCP( List( [2..6], n -> SymmetricGroup(n)), "WS_IdGroup" );
    #I  1/5:master --> localhost:26133
    #I  2/5:master --> localhost:26134
    #I  3/5:master --> localhost:26133
    #I  4/5:master --> localhost:26134
    #I  5/5:master --> localhost:26133
    [ [ 2, 1 ], [ 6, 1 ], [ 24, 12 ], [ 120, 34 ], [ 720, 763 ] ]

Minimal Info level:

    gap> SetInfoLevel(InfoSCSCP,0);
    gap> SetInfoLevel(InfoMasterWorker,0);
    gap> ParListWithSCSCP( List( [2..6], n -> SymmetricGroup(n)), "WS_IdGroup" );
    [ [ 2, 1 ], [ 6, 1 ], [ 24, 12 ], [ 120, 34 ], [ 720, 763 ] ]

Verbose Info level:

    gap> SetInfoLevel(InfoMasterWorker,5);
    gap> ParListWithSCSCP( List( [2..6], n -> SymmetricGroup(n)), "WS_IdGroup" );
    #I  1/5:master --> localhost:26133 : SymmetricGroup( [ 1 .. 2 ] )
    #I  2/5:master --> localhost:26134 : SymmetricGroup( [ 1 .. 3 ] )
    #I  localhost:26133 --> 1/5:master : [ 2, 1 ]
    #I  3/5:master --> localhost:26133 : SymmetricGroup( [ 1 .. 4 ] )
    #I  localhost:26134 --> 2/5:master : [ 6, 1 ]
    #I  4/5:master --> localhost:26134 : SymmetricGroup( [ 1 .. 5 ] )
    #I  localhost:26133 --> 3/5:master : [ 24, 12 ]
    #I  5/5:master --> localhost:26133 : SymmetricGroup( [ 1 .. 6 ] )
    #I  localhost:26134 --> 4/5:master : [ 120, 34 ]
    #I  localhost:26133 --> 5/5:master : [ 720, 763 ]
    [ [ 2, 1 ], [ 6, 1 ], [ 24, 12 ], [ 120, 34 ], [ 720, 763 ] ]
    gap> SetInfoLevel(InfoMasterWorker,2);

#### 9.3 Other SCSCP Utilities

##### 9.3-1 DateISO8601

`‣ DateISO8601`( ) | ( function )

Returns: string

Returns the current date in the ISO-8601 YYYY-MM-DD format. This is an internal function of the package which is used by the SCSCP server to generate the transient content dictionary, accordingly to the definition of the OpenMath symbol `meta.CDDate`.

    gap> DateISO8601();
    "2017-02-05"

##### 9.3-2 CurrentTimestamp

`‣ CurrentTimestamp`( ) | ( function )

Returns: string

Returns the result of the call to `date`. This is an internal function of the package which is used to add the timestamp to the SCSCP service description.

    gap> CurrentTimestamp();
    "Tue 30 Jan 2017 11:19:38 BST"

##### 9.3-3 Hostname

`‣ Hostname`( ) | ( function )

Returns: string

Returns the result of the call to `hostname`. This function may be used in the configuration file `scscp/config.g` to specify that the default hostname which will be used by the SCSCP server will be detected automatically using `hostname`.

    gap> Hostname();
    "scscp.gap-system.org"

##### 9.3-4 MemoryUsageByGAPinKbytes

`‣ MemoryUsageByGAPinKbytes`( ) | ( function )

Returns: integer

Returns the current volume of the memory used by GAP in kylobytes. This is equivalent to calling `ps -p <PID> -o vsz`, where `<PID>` is the process ID of the GAP process. This is an internal function of the package which is used by the SCSCP server to report its memory usage in the `info_memory` attribute when being called with the option `debuglevel=2` (see options in `EvaluateBySCSCP` (6.3-1) and `NewProcess` (6.2-2)).

    gap> MemoryUsageByGAPinKbytes();
    649848

##### 9.3-5 LastReceivedCallID

`‣ LastReceivedCallID`( ) | ( function )

Returns: string

Returns the call ID contained in the most recently received message. It may contain some useful debugging information; in particular, the call ID for the GAP SCSCP client and server contains colon-separated server name, port number, process ID and a random string.

    gap> LastReceivedCallID();
    "scscp.gap-system.org:26133:77372:choDZBgA"

##### 9.3-6 IO_PickleToString

`‣ IO_PickleToString`( obj ) | ( function )

Returns: string containing "pickled" object

This function "pickles" or "serialises" the object obj using the operation `IO_Pickle` (IO: IO_Pickle) from the IO package, and writes it to a string, from which it could be later restored using `IO_UnpickleFromString` (9.3-7). This provides a way to design SCSCP procedures which transmit GAP objects in the "pickled" format as OpenMath strings, which may be useful for objects which may be "pickled" by the IO package but can not be converted to OpenMath or for which the "pickled" representation is more compact or can be encoded/decoded much faster.

See `IO_Pickle` (IO: IO_Pickle) and `IO_Unpickle` (IO: IO_Unpickle) for more details.

    gap> f := IO_PickleToString( GF( 125 ) );
    "FFIEINTG\>15INTG\>13FAIL"

##### 9.3-7 IO_UnpickleFromString

`‣ IO_UnpickleFromString`( s ) | ( function )

Returns: "unpickled" GAP object

This function "unpickles" the string s which was created using the function `IO_PickleToString` (9.3-6), using the operation `IO_Unpickle` (IO: IO_Unpickle) from the IO package. See `IO_PickleToString` (9.3-6) for more details and suggestions about its usage.

    gap> IO_UnpickleFromString( f );
    GF(5^3)
    gap> f = IO_UnpickleFromString( IO_PickleToString( f ) );
    true

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