X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=futex-wakeup%2Fnto1-selective%2Ffutex.spin;fp=futex-wakeup%2Fnto1-selective%2Ffutex.spin;h=6f854fceefba73dfbc3781d04734b75590175159;hb=fda9aff00dcdf7cb49892d79f861d0acfb475514;hp=556f96fad7b175aa5bc78879aa25e99917ab3680;hpb=7f12dad2ba26c922477cc5999f7efef43ce26748;p=urcu.git

diff --git a/futex-wakeup/nto1-selective/futex.spin b/futex-wakeup/nto1-selective/futex.spin
index 556f96f..6f854fc 100644
--- a/futex-wakeup/nto1-selective/futex.spin
+++ b/futex-wakeup/nto1-selective/futex.spin
@@ -3,48 +3,56 @@
  * futex wakeup algorithm.
  *
  * In this model, waker threads are told whether they are still being
- * waited on, and skip the futex wakeup if not.
- *
+ * waited on, and skip the futex wakeup if not. The waiter progresses
+ * each time it sees data in both queues.
+
  * Algorithm verified :
  *
- * queue = 0;
- * waiting = 0;
- * gp_futex = 0;
- * gp = 1;
+ * queue[n] = 0;
+ * futex = 0;
+ * futex_wake = 0;
  *
- *                          Waker
- *                          while (1) {
- *                            this.queue = gp;
- *                            if (this.waiting == 1) {
- *                              this.waiting = 0;
- *                              if (gp_futex == -1) {
- *                                gp_futex = 0;
- *                                futex_wake = 1;
- *                              }
+ *                          n wakers (2 loops)
+ *
+ *                          queue[pid] = 1;
+ *                          if (futex == -1) {
+ *                            if (waker[pid].waiting == 1) {
+ *                              waker[pid].waiting = 0;
+ *                              futex = 0;
+ *                              futex_wake = 1;
  *                            }
  *                          }
  *
- * Waiter
- * in_registry = 1;
+ * 1 waiter
+ *
  * while (1) {
- *   gp_futex = -1;
- *   waiting |= (queue != gp);
- *   in_registry &= (queue != gp);
- *   if (all in_registry == 0) {
- * progress:
- *     gp_futex = 0;
- *     gp = !gp;
- *     restart;
- *   } else {
- *     futex_wake = (gp_futex == -1 ? 0 : 1);
- *     while (futex_wake == 0) { }
+ *   futex = -1;
+ *   waker[0].waiting = 1;
+ *   waker[1].waiting = 1;
+ *   while (!(queue[0] == 1 && queue[1] == 1)) {
+ *       if (futex == -1) {
+ *         futex_wake = (futex == -1 ? 0 : 1);  (atomic)
+ *         while (futex_wake == 0) { };
+ *       }
+ *     }
  *   }
- *   queue = 0;
+ *   futex = 0;
+ *   waker[0].waiting = 0;
+ *   waker[1].waiting = 0;
+ * progress:
+ *   queue[0] = 0;
+ *   queue[1] = 0;
  * }
  *
- * By testing progress, i.e. [] <> !np_, we check that an infinite sequence
- * of update_counter_and_wait (and consequently of synchronize_rcu) will
- * not block.
+ * if queue = 1, then !_np
+ *
+ * By testing progress, i.e. [] <> ((!np_) || (!queue_has_entry)), we
+ * check that we can never block forever if there is an entry in the
+ * any of the queues.
+ *
+ * The waker performs only 2 loops (and NOT an infinite number of loops)
+ * because we really want to see what happens when the waker stops
+ * enqueuing.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -67,97 +75,106 @@
 
 int queue[2] = 0;
 int waiting[2] = 0;
+int futex = 0;
 int futex_wake = 0;
-int gp_futex = 0;
-int gp = 1;
-int in_registry[2] = 0;
 
 active [2] proctype waker()
 {
 	assert(get_pid() < 2);
 
-	do
-	:: 1 ->
-		queue[get_pid()] = gp;
-	
+	/* loop 1 */
+	queue[get_pid()] = 1;
+
+	if
+	:: (futex == -1) ->
 		if
-		:: (waiting[get_pid()] == 1) ->
+		:: (waiting[get_pid() == 1]) ->
 			waiting[get_pid()] = 0;
-			if
-			:: (gp_futex == -1) ->
-				gp_futex = 0;
-#ifndef INJ_QUEUE_NO_WAKE
-				futex_wake = 1;
-#endif
-			:: else ->
-				skip;
-			fi;
+			futex = 0;
+			futex_wake = 1;
+		:: else -> skip;
 		fi;
-	od;
+	:: else ->
+		skip;
+	fi;
+
+	/* loop 2 */
+	queue[get_pid()] = 1;
+
+	if
+	:: (futex == -1) ->
+		if
+		:: (waiting[get_pid() == 1]) ->
+			waiting[get_pid()] = 0;
+			futex = 0;
+			futex_wake = 1;
+		:: else -> skip;
+		fi;
+	:: else ->
+		skip;
+	fi;
+
+#ifdef INJ_QUEUE_NO_WAKE
+	/* loop 3 */
+	queue[get_pid()] = 1;
+#endif
 }
 
 
 active proctype waiter()
 {
-restart:
-	in_registry[0] = 1;
-	in_registry[1] = 1;
 	do
 	:: 1 ->
-#if (!defined(INJ_LATE_DEC) && !defined(INJ_INVERT_WAITING_VS_GP_FUTEX))
-		gp_futex = -1;
+#ifndef INJ_LATE_DEC
+		futex = -1;
+		waiting[0] = 1;
+		waiting[1] = 1;
 #endif
-		if
-		:: (in_registry[0] == 1 && queue[0] != gp) ->
+
+		do
+		:: 1 ->
+			if
+			:: (queue[0] == 1 || queue[1] == 1) ->
+				break;
+			:: else ->
+				skip;
+			fi;
+#ifdef INJ_LATE_DEC
+			futex = -1;
 			waiting[0] = 1;
-                :: else ->
-		        skip;
-		fi;
-		if
-		:: (in_registry[1] == 1 && queue[1] != gp) ->
 			waiting[1] = 1;
-                :: else ->
-		        skip;
-		fi;
-
-		if
-		:: (in_registry[0] == 1 && queue[0] == gp) ->
-			in_registry[0] = 0;
-		:: else ->
-			skip;
-		fi;
-		if
-		:: (in_registry[1] == 1 && queue[1] == gp) ->
-			in_registry[1] = 0;
-		:: else ->
-			skip;
-		fi;
-#ifdef INJ_INVERT_WAITING_VS_GP_FUTEX
-		gp_futex = -1;
 #endif
+			if
+			:: (futex == -1) ->
+				atomic {
+					if
+					:: (futex == -1) ->
+						futex_wake = 0;
+					:: else ->
+						futex_wake = 1;
+					fi;
+				}
+				/* block */
+				do
+				:: 1 ->
+					if
+					:: (futex_wake == 0) ->
+						skip;
+					:: else ->
+						break;
+					fi;
+				od;
+			:: else ->
+				skip;
+			fi;
+		od;
 
-		if
-		:: (in_registry[0] == 0 && in_registry[1] == 0) ->
-progress:
-#ifndef INJ_LATE_DEC
-			gp_futex = 0;
-#endif
-			gp = !gp;
-			goto restart;
-		:: else ->
-#ifdef INJ_LATE_DEC
-			gp_futex = -1;
-#endif
-			futex_wake = gp_futex + 1;
-			do
-			:: 1 ->
-				if
-				:: (futex_wake == 0) ->
-					skip;
-				:: else ->
-					break;
-				fi;
-			od;
-		fi;
+		futex = 0;
+		waiting[0] = 0;
+		waiting[1] = 0;
+progress:	/* progress on dequeue */
+		queue[0] = 0;
+		queue[1] = 0;
 	od;
+
 }