Bulletin number:  31
Products affected: D711D
Description: Very long timeouts on chan-in-*-t routines
Component: crtl.lib
Date: Wed Mar 14 10:29:45 GMT 1990
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The mechanism used for input timeouts in Parallel C is slightly
strange.  This is my explanation of it.

The input transfer is initiated and the process waits.  The wait time
is about one eighth of the timeout value.  The transfer is then
checked for completion.  If complete the routine returns.  If not,
another one eighth of the timeout value is waited.  This means that
the time to transfer data is more dependant on the timeout value than
on the quantity of data to be input.

3L have supplied a floppy disk which contains an "experimental"
version of the affected routines.  The library was provided on the
understanding that it will not be put on general release but will only
be provided to customers who have a specific need for it.  Each office
will receive a copy shortly.

The following is the READ.ME file provided with the disk.

----------------------------------------------------------------------

                            CHANTIME.BIN

     Replacement timeout functions for Parallel C V2.0


This disk holds a file CHANTIME.BIN which contains T4 and T8 versions
of  an experimental revision  of the "timeout" channel functions  for
Parallel  C.   The revised functions  behave in the same way  to  the
originals  when the communication times out, but may return with much
less  delay when the  communication is successful.  The package  also
includes  a function which can be used to vary the behaviour of these
functions to tune them to different applications.

The  provision of the functions in this way does not guarantee that a
future  version  of  Parallel  C  will include  functions  with  this
specification.

The "timeout" channel functions included in this library are
as follows:

          chan_in_byte_tx          chan_out_byte_tx
          chan_in_word_tx          chan_out_word_tx
          chan_in_message_tx       chan_out_message_tx

The names of the revised functions are thus identical to the standard
functions  included  with Parallel  C, with a lower-case  letter  'x'
added.   The argument and result types for the functions are the same
as for the originals.

In   addition,  the  CHANTIME.BIN  library  includes  an   additional
function, described as follows:

          void chan_t_granularity(i)
          int i;

This  sets  the  maximum  time  (in  ticks of  the  current  priority
processor  clock) between a communication completing and the  timeout
function  returning.  The default value for this "granularity" is 100
ticks  (about  7ms at  low  priority, 100us at high  priority).   The
behaviour  of the revised functions can be made identical to those of
the  original  functions  supplied  with Parallel C V2.0  by  calling
chan_t_granularity  with a value of 0x7FFFFFFF (the maximum  positive
integer).   The functions then revert to a granularity of one  eighth
of the specified timeout value.