From c8072f7b36603a68b56fb22ffb1d0a98ae87cdb0 Mon Sep 17 00:00:00 2001
From: Simon Marlow <marlowsd@gmail.com>
Date: Fri, 6 Feb 2009 13:06:09 +0000
Subject: [PATCH] add debugging code and comments
---
rts/parallel/WSDeque.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/rts/parallel/WSDeque.c b/rts/parallel/WSDeque.c
index ec34a8ca25d..e7fd58ae928 100644
--- a/rts/parallel/WSDeque.c
+++ b/rts/parallel/WSDeque.c
@@ -30,7 +30,11 @@
* are synchronised without a lock, based on a cas of the top
* position. One reader wins, the others return NULL for a failure.
*
- * Both popBottom and steal also return NULL when the queue is empty.
+ * Both popWSDeque and stealWSDeque also return NULL when the queue is empty.
+ *
+ * Testing: see testsuite/tests/ghc-regress/rts/testwsdeque.c. If
+ * there's anything wrong with the deque implementation, this test
+ * will probably catch it.
*
* ---------------------------------------------------------------------------*/
@@ -140,6 +144,7 @@ popWSDeque (WSDeque *q)
}
removed = *pos;
if (currSize > 0) { /* no danger, still elements in buffer after b-- */
+ // debugBelch("popWSDeque: t=%ld b=%ld = %ld\n", t, b, removed);
return removed;
}
/* otherwise, has someone meanwhile stolen the same (last) element?
@@ -153,6 +158,8 @@ popWSDeque (WSDeque *q)
ASSERT_WSDEQUE_INVARIANTS(q);
ASSERT(q->bottom >= q->top);
+ // debugBelch("popWSDeque: t=%ld b=%ld = %ld\n", t, b, removed);
+
return removed;
}
@@ -176,7 +183,8 @@ stealWSDeque_ (WSDeque *q)
t = q->top;
// NB. b and t are unsigned; we need a signed value for the test
- // below.
+ // below, because it is possible that t > b during a
+ // concurrent popWSQueue() operation.
if ((long)b - (long)t <= 0 ) {
return NULL; /* already looks empty, abort */
}
@@ -193,6 +201,8 @@ stealWSDeque_ (WSDeque *q)
return NULL;
} /* else: OK, top has been incremented by the cas call */
+ // debugBelch("stealWSDeque_: t=%d b=%d\n", t, b);
+
// Can't do this on someone else's spark pool:
// ASSERT_WSDEQUE_INVARIANTS(q);
@@ -211,6 +221,9 @@ stealWSDeque (WSDeque *q)
return stolen;
}
+/* -----------------------------------------------------------------------------
+ * pushWSQueue
+ * -------------------------------------------------------------------------- */
#define DISCARD_NEW
--
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