X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-pointer-static.h;fp=urcu-pointer-static.h;h=c2ba80025a2703b7edd69ac017ecc5cb9b57d1bc;hp=0000000000000000000000000000000000000000;hb=7e30abe3df0e83eeb741bfc18d07cb016af804a1;hpb=074d8438a30f7da8ae12eb94caff69c37fb576bd

diff --git a/urcu-pointer-static.h b/urcu-pointer-static.h
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+#ifndef _URCU_POINTER_STATIC_H
+#define _URCU_POINTER_STATIC_H
+
+/*
+ * urcu-pointer-static.h
+ *
+ * Userspace RCU header. Operations on pointers.
+ *
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-pointer.h for
+ * linking dynamically with the userspace rcu library.
+ *
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
+ *
+ * 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.
+ */
+
+#include <urcu/compiler.h>
+#include <urcu/arch.h>
+#include <urcu/system.h>
+#include <urcu/arch_uatomic.h>
+
+/**
+ * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
+ * into a RCU read-side critical section. The pointer can later be safely
+ * dereferenced within the critical section.
+ *
+ * This ensures that the pointer copy is invariant thorough the whole critical
+ * section.
+ *
+ * Inserts memory barriers on architectures that require them (currently only
+ * Alpha) and documents which pointers are protected by RCU.
+ *
+ * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
+ * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
+ * data read before the pointer read by speculating the value of the pointer.
+ * Correct ordering is ensured because the pointer is read as a volatile access.
+ * This acts as a global side-effect operation, which forbids reordering of
+ * dependent memory operations. Note that such concern about dependency-breaking
+ * optimizations will eventually be taken care of by the "memory_order_consume"
+ * addition to forthcoming C++ standard.
+ *
+ * Should match rcu_assign_pointer() or rcu_xchg_pointer().
+ */
+
+#define _rcu_dereference(p)     ({					\
+				typeof(p) _________p1 = LOAD_SHARED(p); \
+				smp_read_barrier_depends();		\
+				(_________p1);				\
+				})
+
+/**
+ * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
+ * is as expected by "old". If succeeds, returns the previous pointer to the
+ * data structure, which can be safely freed after waiting for a quiescent state
+ * using synchronize_rcu(). If fails (unexpected value), returns old (which
+ * should not be freed !).
+ */
+
+#define _rcu_cmpxchg_pointer(p, old, _new)		\
+	({						\
+		if (!__builtin_constant_p(_new) ||	\
+		    ((_new) != NULL))			\
+			wmb();				\
+		uatomic_cmpxchg(p, old, _new);		\
+	})
+
+/**
+ * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
+ * pointer to the data structure, which can be safely freed after waiting for a
+ * quiescent state using synchronize_rcu().
+ */
+
+#define _rcu_xchg_pointer(p, v)				\
+	({						\
+		if (!__builtin_constant_p(v) ||		\
+		    ((v) != NULL))			\
+			wmb();				\
+		uatomic_xchg(p, v);			\
+	})
+
+
+#define _rcu_set_pointer(p, v)				\
+	({						\
+		if (!__builtin_constant_p(v) || 	\
+		    ((v) != NULL))			\
+			wmb();				\
+		STORE_SHARED(*(p), v);			\
+	})
+
+/*
+ * _rcu_publish_content - Exchanges the pointer and waits for quiescent state.
+ *
+ * The pointer returned can be freed.
+ */
+#define _rcu_publish_content(p, v)			\
+	({						\
+		void *oldptr;				\
+		oldptr = _rcu_xchg_pointer(p, v);	\
+		synchronize_rcu();			\
+		oldptr;					\
+	})
+
+/**
+ * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
+ * meant to be read by RCU read-side critical sections. Returns the assigned
+ * value.
+ *
+ * Documents which pointers will be dereferenced by RCU read-side critical
+ * sections and adds the required memory barriers on architectures requiring
+ * them. It also makes sure the compiler does not reorder code initializing the
+ * data structure before its publication.
+ *
+ * Should match rcu_dereference_pointer().
+ */
+
+#define _rcu_assign_pointer(p, v)	_rcu_set_pointer(&(p), v)
+
+#endif /* _URCU_POINTER_STATIC_H */