1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
4 // SPDX-License-Identifier: LGPL-2.1-or-later
6 #ifndef _URCU_QSBR_STATIC_H
7 #define _URCU_QSBR_STATIC_H
10 * Userspace RCU QSBR header.
12 * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
13 * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
15 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
24 #include <urcu/debug.h>
25 #include <urcu/compiler.h>
26 #include <urcu/arch.h>
27 #include <urcu/system.h>
28 #include <urcu/uatomic.h>
29 #include <urcu/list.h>
30 #include <urcu/futex.h>
31 #include <urcu/tls-compat.h>
32 #include <urcu/static/urcu-common.h>
39 * This code section can only be included in LGPL 2.1 compatible source code.
40 * See below for the function call wrappers which can be used in code meant to
41 * be only linked with the Userspace RCU library. This comes with a small
42 * performance degradation on the read-side due to the added function calls.
43 * This is required to permit relinking with newer versions of the library.
46 #define URCU_QSBR_GP_ONLINE (1UL << 0)
47 #define URCU_QSBR_GP_CTR (1UL << 1)
49 extern struct urcu_gp urcu_qsbr_gp
;
51 struct urcu_qsbr_reader
{
52 /* Data used by both reader and synchronize_rcu() */
54 /* Data used for registry */
55 struct cds_list_head node
__attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
58 /* Reader registered flag, for internal checks. */
59 unsigned int registered
:1;
62 extern DECLARE_URCU_TLS(struct urcu_qsbr_reader
, urcu_qsbr_reader
);
65 * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
67 static inline void urcu_qsbr_wake_up_gp(void)
69 if (caa_unlikely(_CMM_LOAD_SHARED(URCU_TLS(urcu_qsbr_reader
).waiting
))) {
70 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader
).waiting
, 0);
72 if (uatomic_read(&urcu_qsbr_gp
.futex
) != -1)
74 uatomic_set(&urcu_qsbr_gp
.futex
, 0);
76 * Ignoring return value until we can make this function
77 * return something (because urcu_die() is not publicly
80 (void) futex_noasync(&urcu_qsbr_gp
.futex
, FUTEX_WAKE
, 1,
85 static inline enum urcu_state
urcu_qsbr_reader_state(unsigned long *ctr
)
89 v
= CMM_LOAD_SHARED(*ctr
);
91 return URCU_READER_INACTIVE
;
92 if (v
== urcu_qsbr_gp
.ctr
)
93 return URCU_READER_ACTIVE_CURRENT
;
94 return URCU_READER_ACTIVE_OLD
;
98 * Enter an RCU read-side critical section.
100 * This function is less than 10 lines long. The intent is that this
101 * function meets the 10-line criterion for LGPL, allowing this function
102 * to be invoked directly from non-LGPL code.
104 static inline void _urcu_qsbr_read_lock(void)
106 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader
).ctr
);
110 * Exit an RCU read-side critical section.
112 * This function is less than 10 lines long. The intent is that this
113 * function meets the 10-line criterion for LGPL, allowing this function
114 * to be invoked directly from non-LGPL code.
116 static inline void _urcu_qsbr_read_unlock(void)
118 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader
).ctr
);
122 * Returns whether within a RCU read-side critical section.
124 * This function is less than 10 lines long. The intent is that this
125 * function meets the 10-line criterion for LGPL, allowing this function
126 * to be invoked directly from non-LGPL code.
128 static inline int _urcu_qsbr_read_ongoing(void)
130 return URCU_TLS(urcu_qsbr_reader
).ctr
;
134 * This is a helper function for _rcu_quiescent_state().
135 * The first cmm_smp_mb() ensures memory accesses in the prior read-side
136 * critical sections are not reordered with store to
137 * URCU_TLS(urcu_qsbr_reader).ctr, and ensures that mutexes held within an
138 * offline section that would happen to end with this
139 * urcu_qsbr_quiescent_state() call are not reordered with
140 * store to URCU_TLS(urcu_qsbr_reader).ctr.
142 static inline void _urcu_qsbr_quiescent_state_update_and_wakeup(unsigned long gp_ctr
)
145 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader
).ctr
, gp_ctr
);
146 cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */
147 urcu_qsbr_wake_up_gp();
152 * Inform RCU of a quiescent state.
154 * This function is less than 10 lines long. The intent is that this
155 * function meets the 10-line criterion for LGPL, allowing this function
156 * to be invoked directly from non-LGPL code.
158 * We skip the memory barriers and gp store if our local ctr already
159 * matches the global urcu_qsbr_gp.ctr value: this is OK because a prior
160 * _rcu_quiescent_state() or _rcu_thread_online() already updated it
161 * within our thread, so we have no quiescent state to report.
163 static inline void _urcu_qsbr_quiescent_state(void)
165 unsigned long gp_ctr
;
167 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader
).registered
);
168 if ((gp_ctr
= CMM_LOAD_SHARED(urcu_qsbr_gp
.ctr
)) == URCU_TLS(urcu_qsbr_reader
).ctr
)
170 _urcu_qsbr_quiescent_state_update_and_wakeup(gp_ctr
);
174 * Take a thread offline, prohibiting it from entering further RCU
175 * read-side critical sections.
177 * This function is less than 10 lines long. The intent is that this
178 * function meets the 10-line criterion for LGPL, allowing this function
179 * to be invoked directly from non-LGPL code.
181 static inline void _urcu_qsbr_thread_offline(void)
183 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader
).registered
);
185 CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader
).ctr
, 0);
186 cmm_smp_mb(); /* write URCU_TLS(urcu_qsbr_reader).ctr before read futex */
187 urcu_qsbr_wake_up_gp();
188 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
192 * Bring a thread online, allowing it to once again enter RCU
193 * read-side critical sections.
195 * This function is less than 10 lines long. The intent is that this
196 * function meets the 10-line criterion for LGPL, allowing this function
197 * to be invoked directly from non-LGPL code.
199 static inline void _urcu_qsbr_thread_online(void)
201 urcu_assert_debug(URCU_TLS(urcu_qsbr_reader
).registered
);
202 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
203 _CMM_STORE_SHARED(URCU_TLS(urcu_qsbr_reader
).ctr
, CMM_LOAD_SHARED(urcu_qsbr_gp
.ctr
));
211 #endif /* _URCU_QSBR_STATIC_H */