1 #ifndef _URCU_BP_STATIC_H
2 #define _URCU_BP_STATIC_H
7 * Userspace RCU header.
9 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
10 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
36 #include <urcu/compiler.h>
37 #include <urcu/arch.h>
38 #include <urcu/system.h>
39 #include <urcu/uatomic.h>
40 #include <urcu/list.h>
41 #include <urcu/tls-compat.h>
42 #include <urcu/debug.h>
45 * This code section can only be included in LGPL 2.1 compatible source code.
46 * See below for the function call wrappers which can be used in code meant to
47 * be only linked with the Userspace RCU library. This comes with a small
48 * performance degradation on the read-side due to the added function calls.
49 * This is required to permit relinking with newer versions of the library.
57 RCU_READER_ACTIVE_CURRENT
,
58 RCU_READER_ACTIVE_OLD
,
63 * The trick here is that RCU_GP_CTR_PHASE must be a multiple of 8 so we can use a
64 * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
66 #define RCU_GP_COUNT (1UL << 0)
67 /* Use the amount of bits equal to half of the architecture long size */
68 #define RCU_GP_CTR_PHASE (1UL << (sizeof(long) << 2))
69 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_PHASE - 1)
72 * Used internally by _rcu_read_lock.
74 extern void rcu_bp_register(void);
78 * Global grace period counter.
79 * Contains the current RCU_GP_CTR_PHASE.
80 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
81 * Written to only by writer with mutex taken.
82 * Read by both writer and readers.
85 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
87 extern struct rcu_gp rcu_gp
;
90 /* Data used by both reader and synchronize_rcu() */
92 /* Data used for registry */
93 struct cds_list_head node
__attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
95 int alloc
; /* registry entry allocated */
99 * Bulletproof version keeps a pointer to a registry not part of the TLS.
100 * Adds a pointer dereference on the read-side, but won't require to unregister
103 extern DECLARE_URCU_TLS(struct rcu_reader
*, rcu_reader
);
105 extern int urcu_bp_has_sys_membarrier
;
107 static inline void urcu_bp_smp_mb_slave(void)
109 if (caa_likely(urcu_bp_has_sys_membarrier
))
115 static inline enum rcu_state
rcu_reader_state(unsigned long *ctr
)
120 return RCU_READER_INACTIVE
;
122 * Make sure both tests below are done on the same version of *value
123 * to insure consistency.
125 v
= CMM_LOAD_SHARED(*ctr
);
126 if (!(v
& RCU_GP_CTR_NEST_MASK
))
127 return RCU_READER_INACTIVE
;
128 if (!((v
^ rcu_gp
.ctr
) & RCU_GP_CTR_PHASE
))
129 return RCU_READER_ACTIVE_CURRENT
;
130 return RCU_READER_ACTIVE_OLD
;
134 * Helper for _rcu_read_lock(). The format of rcu_gp.ctr (as well as
135 * the per-thread rcu_reader.ctr) has the upper bits containing a count of
136 * _rcu_read_lock() nesting, and a lower-order bit that contains either zero
137 * or RCU_GP_CTR_PHASE. The smp_mb_slave() ensures that the accesses in
138 * _rcu_read_lock() happen before the subsequent read-side critical section.
140 static inline void _rcu_read_lock_update(unsigned long tmp
)
142 if (caa_likely(!(tmp
& RCU_GP_CTR_NEST_MASK
))) {
143 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
)->ctr
, _CMM_LOAD_SHARED(rcu_gp
.ctr
));
144 urcu_bp_smp_mb_slave();
146 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
)->ctr
, tmp
+ RCU_GP_COUNT
);
150 * Enter an RCU read-side critical section.
152 * The first cmm_barrier() call ensures that the compiler does not reorder
153 * the body of _rcu_read_lock() with a mutex.
155 * This function and its helper are both less than 10 lines long. The
156 * intent is that this function meets the 10-line criterion in LGPL,
157 * allowing this function to be invoked directly from non-LGPL code.
159 static inline void _rcu_read_lock(void)
163 if (caa_unlikely(!URCU_TLS(rcu_reader
)))
164 rcu_bp_register(); /* If not yet registered. */
165 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
166 tmp
= URCU_TLS(rcu_reader
)->ctr
;
167 urcu_assert((tmp
& RCU_GP_CTR_NEST_MASK
) != RCU_GP_CTR_NEST_MASK
);
168 _rcu_read_lock_update(tmp
);
172 * Exit an RCU read-side critical section. This function is less than
173 * 10 lines of code, and is intended to be usable by non-LGPL code, as
174 * called out in LGPL.
176 static inline void _rcu_read_unlock(void)
180 tmp
= URCU_TLS(rcu_reader
)->ctr
;
181 urcu_assert(tmp
& RCU_GP_CTR_NEST_MASK
);
182 /* Finish using rcu before decrementing the pointer. */
183 urcu_bp_smp_mb_slave();
184 _CMM_STORE_SHARED(URCU_TLS(rcu_reader
)->ctr
, tmp
- RCU_GP_COUNT
);
185 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
189 * Returns whether within a RCU read-side critical section.
191 * This function is less than 10 lines long. The intent is that this
192 * function meets the 10-line criterion for LGPL, allowing this function
193 * to be invoked directly from non-LGPL code.
195 static inline int _rcu_read_ongoing(void)
197 if (caa_unlikely(!URCU_TLS(rcu_reader
)))
198 rcu_bp_register(); /* If not yet registered. */
199 return URCU_TLS(rcu_reader
)->ctr
& RCU_GP_CTR_NEST_MASK
;
206 #endif /* _URCU_BP_STATIC_H */