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_MB_STATIC_H
7 #define _URCU_MB_STATIC_H
10 * Userspace RCU 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.
23 #include <urcu/debug.h>
24 #include <urcu/config.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 extern struct urcu_gp urcu_mb_gp
;
48 extern DECLARE_URCU_TLS(struct urcu_reader
, urcu_mb_reader
);
51 * Helper for _urcu_mb_read_lock(). The format of urcu_mb_gp.ctr (as well as
52 * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of
53 * _urcu_mb_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit
54 * that contains either zero or one. The cmm_smp_mb() ensures that the accesses in
55 * _urcu_mb_read_lock() happen before the subsequent read-side critical section.
57 static inline void _urcu_mb_read_lock_update(unsigned long tmp
)
59 if (caa_likely(!(tmp
& URCU_GP_CTR_NEST_MASK
))) {
60 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader
).ctr
, _CMM_LOAD_SHARED(urcu_mb_gp
.ctr
));
63 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader
).ctr
, tmp
+ URCU_GP_COUNT
);
67 * Enter an RCU read-side critical section.
69 * The first cmm_barrier() call ensures that the compiler does not reorder
70 * the body of _urcu_mb_read_lock() with a mutex.
72 * This function and its helper are both less than 10 lines long. The
73 * intent is that this function meets the 10-line criterion in LGPL,
74 * allowing this function to be invoked directly from non-LGPL code.
76 static inline void _urcu_mb_read_lock(void)
80 urcu_assert_debug(URCU_TLS(urcu_mb_reader
).registered
);
82 tmp
= URCU_TLS(urcu_mb_reader
).ctr
;
83 urcu_assert_debug((tmp
& URCU_GP_CTR_NEST_MASK
) != URCU_GP_CTR_NEST_MASK
);
84 _urcu_mb_read_lock_update(tmp
);
88 * This is a helper function for _urcu_mb_read_unlock().
90 * The first cmm_smp_mb() call ensures that the critical section is
91 * seen to precede the store to rcu_reader.ctr.
92 * The second cmm_smp_mb() call ensures that we write to rcu_reader.ctr
93 * before reading the update-side futex.
95 static inline void _urcu_mb_read_unlock_update_and_wakeup(unsigned long tmp
)
97 if (caa_likely((tmp
& URCU_GP_CTR_NEST_MASK
) == URCU_GP_COUNT
)) {
99 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader
).ctr
, tmp
- URCU_GP_COUNT
);
101 urcu_common_wake_up_gp(&urcu_mb_gp
);
103 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader
).ctr
, tmp
- URCU_GP_COUNT
);
107 * Exit an RCU read-side critical section. Both this function and its
108 * helper are smaller than 10 lines of code, and are intended to be
109 * usable by non-LGPL code, as called out in LGPL.
111 static inline void _urcu_mb_read_unlock(void)
115 urcu_assert_debug(URCU_TLS(urcu_mb_reader
).registered
);
116 tmp
= URCU_TLS(urcu_mb_reader
).ctr
;
117 urcu_assert_debug(tmp
& URCU_GP_CTR_NEST_MASK
);
118 _urcu_mb_read_unlock_update_and_wakeup(tmp
);
119 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
123 * Returns whether within a RCU read-side critical section.
125 * This function is less than 10 lines long. The intent is that this
126 * function meets the 10-line criterion for LGPL, allowing this function
127 * to be invoked directly from non-LGPL code.
129 static inline int _urcu_mb_read_ongoing(void)
131 return URCU_TLS(urcu_mb_reader
).ctr
& URCU_GP_CTR_NEST_MASK
;
138 #endif /* _URCU_MB_STATIC_H */
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