Re: Help me to solve this problem!

[jb@rti.UUCP (Jeff Bartlett)]

In article <8708241839.AA01159@ucbvax.Berkeley.EDU>, ie53@NTSUVAX.BITNET (HAERIM LEE) writes:

 > procedure imore is      -- Intelligent 'more'
 > 

 > This program is similar to 'more' on Unix except its more
 > clever default behavior; that is, it keeps printing each
  .....
 > "next screen" is printed, and it was sitting idle until I hit
 > the <space bar>.  I noticed that this is because the 'get'
 > statement in the main body does not return its control to
 > the task 'mon_user' when it is suspended (Is it?) by this input
 > operation, while the task 'mon_user' was already in a suspended
 > state and possibly in a ready state if the specified delay time
 > had passed.  In this case, the control should be given 'mon_user'
 > so that the procedure call 'print_next' after the delay state-
 > ment can be executed.  Actually, I found that the task 'mon_user'
 > did NOT become suspended when the 'get' was invoked, but remained
 > as a 'running' state.  This can be shown using the VAX/VMS Symbolic
 > Debugger.

 > Shouldn't the state of the task 'mon_user' become
 > 'suspended' when the 'get' is called, if there are any 'ready'
 > tasks?  If not, how do we easily implement such time-bombs for
 > input operations?  What is the relationship between task states
 > and i/o operations?  In Ada, are i/o operations done synchronously
 > or asynchronously?  Seems to be 'synchronous' in the Vax Ada V1.3.
 >
 > --    Haerim Lee (IE53@NTSUVAX)

See section 2.7 "Input-Output and Tasking" in "VAX Ada Programmer's Run-Time
Reference Manual", p 2-73.

I/O on SYS$INPUT, SYS$OUTPUT, SYS$COMMAND, and SYS$ERROR are 'synchronous'.
TEXT_IO used ADA$INPUT and ADA$OUTPUT which is normally assigned to SYS$INPUT
and SYS$OUTPUT.  To get 'async' i/o, assign ADA$INPUT and ADA$OUTPUT to TT: in
DCL.

Jeff Bartlett
Center for Digital Systems Research
Research Triangle Institute
jb@rti.rti.org