Changeset a3af522

Timestamp:

Nov 11, 2024, 10:32:08 PM (30 hours ago)

Author:

Peter A. Buhr <pabuhr@…>

Branches:

master

Children:

b5f1e850

Parents:

41882628

Message:

first attempt at updating barrier lock

File:

• libcfa/src/concurrency/barrier.hfa (modified) (2 diffs)

libcfa/src/concurrency/barrier.hfa

@@ -1 @@
-//
+//                               -*- Mode: C -*- 
+// 
 // Cforall Version 1.0.0 Copyright (C) 2022 University of Waterloo
-//
+// 
 // The contents of this file are covered under the licence agreement in the
 // file "LICENCE" distributed with Cforall.
 //
-// barrier.hfa -- simple barrier implemented from monitors
-//
-// Author           : Thierry Delisle
-// Created On       : Thu Mar 31 16:51:35 2022
-// Last Modified By :
-// Last Modified On :
-// Update Count     :
-//
+// barrier.hfa -- simple barrier implemented using a monitor
+// 
+// Author           : Peter A. Buhr
+// Created On       : Sun Nov 10 08:07:35 2024
+// Last Modified By : Peter A. Buhr
+// Last Modified On : Sun Nov 10 08:11:55 2024
+// Update Count     : 3
+// 
 
 #pragma once
@@ -18 +19 @@
 #include <monitor.hfa>
 
-// Simple barrier based on a monitor
+// Plan 9 inheritance does not work with monitors. Two monitor locks are created.
+
 monitor barrier {
-        // Number of threads blocking needed to unblock the barrier
-        // Unsigned should be enough, I don't expect use cases with 2^32 thread barriers.
-        unsigned width;
-
-        // Current count (counting backwards)
-        unsigned count;
-
-        // Barrier uses internal scheduling
-        condition c;
+        unsigned int group, arrivals;                                           // group size, arrival counter
+        condition c;                                                                            // wait for group to form
 };
 
 // Constructor
-void ?{}( barrier & this, unsigned width ) {
-        this.width = width;
-        this.count = width; // Count backwards so initialize at width
+void ?{}( barrier & b, unsigned group ) {
+        b.group = b.arrivals = group;                                           // count backwards
 }
 
-// block until the number of threads needed have blocked
-// returns an value indicating the reverse order the threads arrived in
-// i.e. last thread will return 0 (and not block)
-//      second last thread returns 1
-//      etc.
-// last is an optional hook that will be called by the last thread
-// before unblocking the others
-static inline unsigned block(barrier & mutex this, fptr_t last = (fptr_t)0 ) {
-        this.count -= 1; // prefix decrement so we the last is 0 and not 1
-        unsigned arrival = this.count; // Note arrival order
-        if(arrival == 0) {
-                if(last) last();
-                // If arrived last unblock everyone and reset
-                signal_all(this.c);
-                this.count = this.width;
-        } else {
-                // Otherwise block
-                wait(this.c);
-        }
-        return arrival; // return arrival order
+// Returns a value indicating the reverse order the threads arrived i.e. last thread returns 0 (and does not block)
+// last is an optional hook that is called by the last thread before unblocking the others.
+static inline unsigned block( barrier & mutex b, fptr_t last = (fptr_t)0 ) with( b ) {
+        arrivals -= 1;                                                                          // prefix decrement so last is 0 not 1
+        unsigned arrived = b.arrivals;                                          // note arrival order
+        if ( arrivals != 0 ) {                                                          // wait for group to form
+                wait( b.c );
+        } else {                                                                                        // group formed
+                if ( last ) last();                                                             // safe to call
+                signal_all( c );                                                                // unblock group
+                arrivals = group;                                                               // reset
+        } // if
+        return arrived;                                                                         // return arrival order
 }