103 lines
2.4 KiB
Plaintext
103 lines
2.4 KiB
Plaintext
(* Version 1.10, Nov 1984 *)
|
||
DEFINITION MODULE Processes;
|
||
(*
|
||
(pseudo-) concurrent programming with SEND/WAIT
|
||
|
||
From the book 'Programming in Modula-2' by Prof.
|
||
N. Wirth.
|
||
*)
|
||
|
||
|
||
EXPORT QUALIFIED
|
||
SIGNAL, SEND, WAIT,
|
||
StartProcess, Awaited, Init;
|
||
|
||
|
||
TYPE
|
||
SIGNAL;
|
||
(*
|
||
- SIGNAL's are the means of synchronization between
|
||
processes. Any variable of type SIGNAL must be
|
||
initialized explizitly by means of procedure
|
||
'Init' before using it with any other procedure
|
||
of this module.
|
||
*)
|
||
|
||
|
||
PROCEDURE StartProcess (P: PROC; n: CARDINAL);
|
||
(*
|
||
- Start up a new process.
|
||
|
||
in: P top-level procedure that will execute in this
|
||
process.
|
||
n number of bytes of workspace to be allocated
|
||
to it.
|
||
|
||
Allocates (from Storage) a workspace of n bytes, and
|
||
creates a process executing procedure P in that workspace.
|
||
Control is given to the new process.
|
||
|
||
Caution: The caller must ensure that the workspace size is
|
||
sufficient for P.
|
||
|
||
Errors: StartProcess may fail due to insufficient memory.
|
||
*)
|
||
|
||
|
||
PROCEDURE SEND (VAR s: SIGNAL);
|
||
(*
|
||
- Send a signal
|
||
|
||
in: s the signal to be sent.
|
||
|
||
out: s the signal with one less process waiting
|
||
for it.
|
||
|
||
If no process is waiting for s, SEND has precisely no
|
||
effect. Otherwise, some process which is waiting for s
|
||
is given control and allowed to continue from WAIT.
|
||
*)
|
||
|
||
|
||
PROCEDURE WAIT (VAR s: SIGNAL);
|
||
(*
|
||
- Wait for some other process to send a signal.
|
||
|
||
in: s the signal to wait for.
|
||
|
||
The current process waits for the signal s. At some later
|
||
time, a SEND(s) by some other process can cause this
|
||
process to return from WAIT.
|
||
|
||
Errors: If all other processes are waiting, WAIT
|
||
terminates the program.
|
||
*)
|
||
|
||
|
||
PROCEDURE Awaited (s:SIGNAL): BOOLEAN;
|
||
(*
|
||
- Test whether any process is waiting for a signal.
|
||
|
||
in: s the signal of interest.
|
||
out: TRUE if and only if at least one process is
|
||
waiting for s.
|
||
*)
|
||
|
||
|
||
PROCEDURE Init (VAR s: SIGNAL);
|
||
(*
|
||
- Initialize a SIGNAL object.
|
||
|
||
in: s the signal to be initialized
|
||
|
||
out: s the initialized signal (ready to be used
|
||
with one of the procedures declared above)
|
||
|
||
An object of type SIGNAL must be initialized with this
|
||
procedure before it can be used with any of the other
|
||
operations. After initilization of s, Awaited(s) is FALSE.
|
||
*)
|
||
|
||
|
||
END Processes.
|
||
|