urcu/annotate: Add CMM annotation
[urcu.git] / include / urcu / static / urcu-signal.h
1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
3 //
4 // SPDX-License-Identifier: LGPL-2.1-or-later
5
6 #ifndef _URCU_SIGNAL_STATIC_H
7 #define _URCU_SIGNAL_STATIC_H
8
9 /*
10 * Userspace RCU header.
11 *
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.
14 *
15 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
16 */
17
18 #include <stdlib.h>
19 #include <pthread.h>
20 #include <unistd.h>
21 #include <stdint.h>
22
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>
33 #include <urcu/static/urcu-signal-nr.h>
34
35 #ifdef __cplusplus
36 extern "C" {
37 #endif
38
39 /*
40 * This code section can only be included in LGPL 2.1 compatible source code.
41 * See below for the function call wrappers which can be used in code meant to
42 * be only linked with the Userspace RCU library. This comes with a small
43 * performance degradation on the read-side due to the added function calls.
44 * This is required to permit relinking with newer versions of the library.
45 */
46
47 extern struct urcu_gp urcu_signal_gp;
48
49 extern DECLARE_URCU_TLS(struct urcu_reader, urcu_signal_reader);
50
51 /*
52 * Helper for _rcu_read_lock(). The format of urcu_signal_gp.ctr (as well as
53 * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of
54 * _rcu_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit
55 * that contains either zero or one. The cmm_barrier() ensures that the accesses in
56 * _rcu_read_lock() happen before the subsequent read-side critical section.
57 */
58 static inline void _urcu_signal_read_lock_update(unsigned long tmp)
59 {
60 if (caa_likely(!(tmp & URCU_GP_CTR_NEST_MASK))) {
61 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, _CMM_LOAD_SHARED(urcu_signal_gp.ctr));
62 cmm_barrier();
63 } else
64 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp + URCU_GP_COUNT);
65 }
66
67 /*
68 * Enter an RCU read-side critical section.
69 *
70 * The first cmm_barrier() call ensures that the compiler does not reorder
71 * the body of _rcu_read_lock() with a mutex.
72 *
73 * This function and its helper are both less than 10 lines long. The
74 * intent is that this function meets the 10-line criterion in LGPL,
75 * allowing this function to be invoked directly from non-LGPL code.
76 */
77 static inline void _urcu_signal_read_lock(void)
78 {
79 unsigned long tmp;
80
81 urcu_assert_debug(URCU_TLS(urcu_signal_reader).registered);
82 cmm_barrier();
83 tmp = URCU_TLS(urcu_signal_reader).ctr;
84 urcu_assert_debug((tmp & URCU_GP_CTR_NEST_MASK) != URCU_GP_CTR_NEST_MASK);
85 _urcu_signal_read_lock_update(tmp);
86 }
87
88 /*
89 * This is a helper function for _rcu_read_unlock().
90 *
91 * The first cmm_barrier() call ensures that the critical section is
92 * seen to precede the store to rcu_reader.ctr.
93 * The second cmm_barrier() call ensures that we write to rcu_reader.ctr
94 * before reading the update-side futex.
95 */
96 static inline void _urcu_signal_read_unlock_update_and_wakeup(unsigned long tmp)
97 {
98 if (caa_likely((tmp & URCU_GP_CTR_NEST_MASK) == URCU_GP_COUNT)) {
99 cmm_barrier();
100 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp - URCU_GP_COUNT);
101 cmm_barrier();
102 urcu_common_wake_up_gp(&urcu_signal_gp);
103 } else
104 _CMM_STORE_SHARED(URCU_TLS(urcu_signal_reader).ctr, tmp - URCU_GP_COUNT);
105 }
106
107 /*
108 * Exit an RCU read-side critical section. Both this function and its
109 * helper are smaller than 10 lines of code, and are intended to be
110 * usable by non-LGPL code, as called out in LGPL.
111 */
112 static inline void _urcu_signal_read_unlock(void)
113 {
114 unsigned long tmp;
115
116 urcu_assert_debug(URCU_TLS(urcu_signal_reader).registered);
117 tmp = URCU_TLS(urcu_signal_reader).ctr;
118 urcu_assert_debug(tmp & URCU_GP_CTR_NEST_MASK);
119 _urcu_signal_read_unlock_update_and_wakeup(tmp);
120 cmm_barrier(); /* Ensure the compiler does not reorder us with mutex */
121 }
122
123 /*
124 * Returns whether within a RCU read-side critical section.
125 *
126 * This function is less than 10 lines long. The intent is that this
127 * function meets the 10-line criterion for LGPL, allowing this function
128 * to be invoked directly from non-LGPL code.
129 */
130 static inline int _urcu_signal_read_ongoing(void)
131 {
132 return URCU_TLS(urcu_signal_reader).ctr & URCU_GP_CTR_NEST_MASK;
133 }
134
135 #ifdef __cplusplus
136 }
137 #endif
138
139 #endif /* _URCU_SIGNAL_STATIC_H */
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