Changeset 31ef267 for libcfa/src/concurrency/barrier.hfa

Timestamp:

Apr 1, 2022, 12:40:35 PM (2 years ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, ast-experimental, enum, master, pthread-emulation, qualifiedEnum

Children:

1417f6b

Parents:

93b8cf4

Message:

Added comments.

File:

• libcfa/src/concurrency/barrier.hfa (modified) (1 diff)

libcfa/src/concurrency/barrier.hfa

@@ -18 +18 @@
 #include <monitor.hfa>
 
+// Simple barrier based on a monitor
 monitor barrier {
-        int max;
-        int count;
+        // 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;
 };
 
-void ?{}( barrier & this, int max ) {
-        this.max = max;
-        this.count = max;
+// Constructor
+void ?{}( barrier & this, unsigned width ) {
+        this.width = width;
+        this.count = width; // Count backwards so initialize at width
 }
 
-static inline int block(barrier & mutex this ) {
-        this.count -= 1;
-        int arrival = this.count;
-        if(arrival != 0) {
+// 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.
+static inline unsigned block(barrier & mutex this ) {
+        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 arrived last unblock everyone and reset
+                signal_all(this.c);
+                this.count = this.width;
+        } else {
+                // Otherwise block
                 wait(this.c);
-        } else {
-                signal_all(this.c);
-                this.count = this.max;
         }
-        return arrival;
+        return arrival; // return arrival order
 }