From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Thu, 17 Sep 2009 15:11:42 +0000 (-0400)
Subject: qsbr: portability fixes: use unsigned long for the gp counters.
X-Git-Tag: v0.1~78
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=f0f7dbdd9ba9bff3860d8aea63a3e01b158351de;p=urcu.git

qsbr: portability fixes: use unsigned long for the gp counters.

unsigned wraps properly in C (modulo ULONG_MAX + 1), IOW ULONG_MAX + 2
_is_ defined and is 1.

Rewrite rcu_gp_ongoing test to work in the unsigned case:

    a - b < 0

becomes

    a - b > ULONG_MAX / 2

This test actually means a - b > 0x7f....f which is exactly what we want
to test for in the first place, but in a portable way.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 8d8aa3f..3d2ec8f 100644
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -32,6 +32,7 @@
 #include <stdlib.h>
 #include <pthread.h>
 #include <assert.h>
+#include <limits.h>
 
 #include <compiler.h>
 #include <arch.h>
@@ -165,18 +166,18 @@ static inline void reader_barrier()
  * Using a int rather than a char to eliminate false register dependencies
  * causing stalls on some architectures.
  */
-extern long urcu_gp_ctr;
+extern unsigned long urcu_gp_ctr;
 
-extern long __thread rcu_reader_qs_gp;
+extern unsigned long __thread rcu_reader_qs_gp;
 
-static inline int rcu_gp_ongoing(long *value)
+static inline int rcu_gp_ongoing(unsigned long *value)
 {
-	long reader_gp;
+	unsigned long reader_gp;
 
 	if (value == NULL)
 		return 0;
 	reader_gp = LOAD_SHARED(*value);
-	return reader_gp && (reader_gp - urcu_gp_ctr < 0);
+	return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
 }
 
 static inline void _rcu_read_lock(void)
diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 1955277..c0e643d 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -42,20 +42,20 @@ pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 /*
  * Global grace period counter.
  */
-long urcu_gp_ctr = 1;
+unsigned long urcu_gp_ctr = 1;
 
 /*
  * Written to only by each individual reader. Read by both the reader and the
  * writers.
  */
-long __thread rcu_reader_qs_gp;
+unsigned long __thread rcu_reader_qs_gp;
 
 /* Thread IDs of registered readers */
 #define INIT_NUM_THREADS 4
 
 struct reader_registry {
 	pthread_t tid;
-	long *rcu_reader_qs_gp;
+	unsigned long *rcu_reader_qs_gp;
 };
 
 #ifdef DEBUG_YIELD
@@ -139,7 +139,7 @@ static void wait_for_quiescent_state(void)
 
 void synchronize_rcu(void)
 {
-	long was_online;
+	unsigned long was_online;
 
 	was_online = rcu_reader_qs_gp;