X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu-static.h;h=1921097dbb8596a9d134fecdea5e2bcfe9444c2d;hp=c47a759d132357a7af23301ece58c238a200d2ec;hb=538d7df5086144837beb7a9c1e2a94eb637b9904;hpb=adcfce542ec1c28796c3c641021a6d37f97b6f6f

diff --git a/urcu-static.h b/urcu-static.h
index c47a759..1921097 100644
--- a/urcu-static.h
+++ b/urcu-static.h
@@ -4,14 +4,27 @@
 /*
  * urcu-static.h
  *
- * Userspace RCU header, to be included only in LGPL-compatible code.
+ * Userspace RCU header.
  *
- * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
+ * dynamically with the userspace rcu library.
  *
- * Credits for Paul E. McKenney <paulmck@linux.vnet.ibm.com>
- * for inspiration coming from the Linux kernel RCU and rcu-preempt.
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
  *
- * Distributed under LGPLv2.1
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  *
  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  */
@@ -104,8 +117,11 @@
 #define YIELD_READ 	(1 << 0)
 #define YIELD_WRITE	(1 << 1)
 
-/* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */
-#ifdef DEBUG_FULL_MB
+/*
+ * Updates without CONFIG_URCU_AVOID_SIGNALS are much slower. Account this in
+ * the delay.
+ */
+#ifdef CONFIG_URCU_AVOID_SIGNALS
 /* maximum sleep delay, in us */
 #define MAX_SLEEP 50
 #else
@@ -148,7 +164,7 @@ static inline void debug_yield_init(void)
 }
 #endif
 
-#ifdef DEBUG_FULL_MB
+#ifdef CONFIG_URCU_AVOID_SIGNALS
 static inline void reader_barrier()
 {
 	smp_mb();
@@ -199,22 +215,16 @@ static inline void _rcu_read_lock(void)
 
 	tmp = urcu_active_readers;
 	/* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
-	/*
-	 * The data dependency "read urcu_gp_ctr, write urcu_active_readers",
-	 * serializes those two memory operations. The memory barrier in the
-	 * signal handler ensures we receive the proper memory commit barriers
-	 * required by _STORE_SHARED and _LOAD_SHARED whenever communication
-	 * with the writer is needed.
-	 */
-	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK)))
+	if (likely(!(tmp & RCU_GP_CTR_NEST_MASK))) {
 		_STORE_SHARED(urcu_active_readers, _LOAD_SHARED(urcu_gp_ctr));
-	else
+		/*
+		 * Set active readers count for outermost nesting level before
+		 * accessing the pointer. See force_mb_all_threads().
+		 */
+		reader_barrier();
+	} else {
 		_STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
-	/*
-	 * Increment active readers count before accessing the pointer.
-	 * See force_mb_all_threads().
-	 */
-	reader_barrier();
+	}
 }
 
 static inline void _rcu_read_unlock(void)
@@ -223,6 +233,9 @@ static inline void _rcu_read_unlock(void)
 	/*
 	 * Finish using rcu before decrementing the pointer.
 	 * See force_mb_all_threads().
+	 * Formally only needed for outermost nesting level, but leave barrier
+	 * in place for nested unlocks to remove a branch from the common case
+	 * (no nesting).
 	 */
 	_STORE_SHARED(urcu_active_readers, urcu_active_readers - RCU_GP_COUNT);
 }
@@ -250,7 +263,7 @@ static inline void _rcu_read_unlock(void)
 
 /**
  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
- * pointer to the data structure, which can be safely freed after waitin for a
+ * pointer to the data structure, which can be safely freed after waiting for a
  * quiescent state using synchronize_rcu().
  */