10/04/85	set_lock_

The set_lock_ subroutine enables cooperating processes to coordinate
their use of shared resources.


Entry points in set_lock_:
   (List is generated by the help command)


:Entry: lock:  10/04/85  set_lock_$lock


Function:	 This entry point attempts to place the lock identifier of
the calling process in the given lock word.


Usage:
declare set_lock_$lock entry (bit(36) aligned, fixed bin,
     fixed bin(35));
call set_lock_$lock (lock_word, wait_time, code);


Arguments:
lock_word
   is the word to be locked.	(Input/Output)
wait_time
   indicates the length of real time, in seconds, that the
   set_lock_$lock entry point should wait for a validly locked lock
   word to be unlocked before returning unsuccessfully.  (Input) A
   value of -1 indicates no time limit.


code
   is a standard status code.	 (Output) It can be one of the following:
   error_table_$invalid_lock_reset
        indicates that the lock word was successfully locked, but the
        lock word previously contained an invalid lock identifier that
        was overwritten
   error_table_$locked_by_this_process
        indicates that the lock word already contained the lock
        identifier of the calling process and was not modified
   error_table_$lock_wait_time_exceeded
        indicates that the lock word contained a valid lock identifier
        of another process and could not be locked in the given time
        limit


   error_table_$no_w_permission
        indicates that calling process does not have proper write
        permission to lock_word


Notes:
It is suggested that set_lock_$lock be called as follows for
applications where efficiency is important:

   if ^stacq (lock_word, static_var_initialized_to_lock_id, ""b)
      then call set_lock_$lock (lock_word, wait_time, code);
      else code = 0;


:Entry: unlock:  10/04/85  set_lock_$unlock


Function:	 This entry point attempts to reset a given lock word to "0"b
and is successful if the lock word contained the lock identifier of the
calling process.


Usage:
declare set_lock_$unlock entry (bit(36) aligned, fixed bin (35));
call set_lock_$unlock (lock_word, code);


Arguments:
lock_word
   is the lock word to be reset.  (Input/Output)
code
   is a standard status code.	 (Output)
   error_table_$lock_not_locked
        indicates that the lock was not locked
   error_table_$locked_by_other_process
        indicates that the lock was not locked by this process and
        therefore was not unlocked
   error_table_$no_w_permission
        indicates that calling process does not have proper write
        permission to lock_word


Notes:
It is suggested that set_lock_$unlock be called as follows for
applications where efficiency is important:

   if ^stacq (lock_word, ""b, static_var_initialized_to_lock_id)
      then call set_lock_$unlock (lock_word, code);
      else code = 0;


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Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

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Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved