Processes



Initiation of Processes

 Processes are created by communication with process DIRECT, in three
 ways:

    * By the arrival of a log-on message from the front-end network.

    * By a (batch) start-up message from SPOOLR.

    * By an operator command to DIRECT:   D/START username

 For an 'interactive' start, DIRECT first checks that the request is
 valid, ie the username is good and the password is correct, and that it
 can be honoured, ie the system is 'open to users'.

 Next, DIRECT checks that the user does not already have as many
 processes running as he is allowed (typically 1 interactive, 1 batch
 and a total of 2).  The 'invocation number' is calculated and this is
 appended to the names of workfiles to make them unique.  DIRECT now
 creates

     a stack file                   #STK n
     a local controller stack file  #LCSTK n
     the Director GLA               #DGLA n
     for an interactive start,
     a terminal buffer              T#IT n
     a user information file        #UINFI n

 If this is done successfully, DIRECT requests Supervisor to start the
 new process.

 The new process is entered via the procedure Director which
 connects

     the System Call table
     DIRLOG
     #UINFI n

 then creates and connects the signal stack, #SIGSTK n and connects
 the nominated basefile (or the default if none is specified or if the
 specified basefile is not available).  Finally, it creates and
 connects the 'base GLA' #BGLA n.  (A total of 7 work files).


Fields in the User Record

 The User Record contains several fields which specify how the process
 should run.  Some of these fields are determined exclusively by the
 System Manager, others are controlled by the process owner.  These
 fields can be set by use of the Director procedure DSFI, invoked either
 from the System Manager's process MANAGR or in a previous invocation of
 the user's process.  Some of the fields may also be set by commands to
 the DIRECT process.  The following is a list of fields relevant to
 process start-up:

           Field                     DSFI TYPE no.     DIRECT command

      Basefile name                     0                D/SETBASEF
      Batch basefile name
                                                         D/BASEF
      Interactive and batch             5
      passwords
      ACR level at which the            7 (priv.)        D/ACR
      process is to run
      Director version number           8 (priv.)
      Process stack file size          10
      Process concurrency limits       14 (priv.)
      Director monitor level           16
      Contingency monitor level        17
      Director monitor file name       19
      Test basefile name               35

 The items marked "priv." may be set only by privileged processes, in
 particular, the MANAGR process.


Entry to the subsystem

 To enter the subsystem, Director proceeds as follows:

    * The processor PC is set to point to the address which is the
      basefile segment address plus the contents of the second word of
      the basefile.

    * The processor LNB is set to the start of the processor stack
      segment, currently local segment 4.

    * The processor SF is set to be 7 words greater than LNB.

    * The processor PSR is set to contain the ACR level equal to that
      specified in the ACR field of the index (see Director procedure
      DSFI, TYPE=7, a zero field in the index specifies the default
      subsystem ACR level, currently 6).  Settings of other PSR bits are
      not specified.

 The subsystem is then entered as though by standard 2900 procedure CALL
 with two 32-bit (integer) parameters.  The two parameters are:

   1) An integer = 1, to be used to achieve compatibility
      in the event of future changes.

   2) The address of the UINFF record.

 The first action of the subsystem should be to copy the GLAP, which
 follows the code in the basefile, into the GLA segment.  Apart from the
 copying, the code which does this may only access the code segment and
 the stack segment.


Process Termination

 When a process terminates under control of Director (as should always
 be the case in principle), Director prints a message in Dirlog
 indicating the reason for stopping.  If the subsystem requested
 termination of the process by calling Director procedure DSTOP, the
 integer parameter REASON is printed. Conventionally, 100 means success
 and values greater than this indicate an error condition detected by
 the Subsystem.  However, if Director initiates the stop sequence, for
 example because a contingency has been incorrectly handled, then a
 REASON less than 100 is printed.