/*
* 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.
*/
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)
/*
* 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);
}
/**
* _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().
*/