1 | /* Copyright 2016 Google Inc. |
2 | |
3 | Licensed under the Apache License, Version 2.0 (the "License"); |
4 | you may not use this file except in compliance with the License. |
5 | You may obtain a copy of the License at |
6 | |
7 | http://www.apache.org/licenses/LICENSE-2.0 |
8 | |
9 | Unless required by applicable law or agreed to in writing, software |
10 | distributed under the License is distributed on an "AS IS" BASIS, |
11 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
12 | See the License for the specific language governing permissions and |
13 | limitations under the License. */ |
14 | |
15 | #include "nsync_cpp.h" |
16 | #include "platform.h" |
17 | #include "compiler.h" |
18 | #include "cputype.h" |
19 | #include "nsync.h" |
20 | #include "atomic.h" |
21 | #include "dll.h" |
22 | #include "sem.h" |
23 | #include "wait_internal.h" |
24 | #include "common.h" |
25 | |
26 | NSYNC_CPP_START_ |
27 | |
28 | /* Internal details of nsync_counter. */ |
29 | struct nsync_counter_s_ { |
30 | nsync_atomic_uint32_ waited; /* wait has been called */ |
31 | nsync_mu counter_mu; /* protects fields below except reads of "value" */ |
32 | nsync_atomic_uint32_ value; /* value of counter */ |
33 | struct nsync_dll_element_s_ *waiters; /* list of waiters */ |
34 | }; |
35 | |
36 | nsync_counter nsync_counter_new (uint32_t value) { |
37 | nsync_counter c = (nsync_counter) malloc (sizeof (*c)); |
38 | if (c != NULL) { |
39 | memset ((void *) c, 0, sizeof (*c)); |
40 | ATM_STORE (&c->value, value); |
41 | } |
42 | return (c); |
43 | } |
44 | |
45 | void nsync_counter_free (nsync_counter c) { |
46 | nsync_mu_lock (&c->counter_mu); |
47 | ASSERT (nsync_dll_is_empty_ (c->waiters)); |
48 | nsync_mu_unlock (&c->counter_mu); |
49 | free (c); |
50 | } |
51 | |
52 | uint32_t nsync_counter_add (nsync_counter c, int32_t delta) { |
53 | uint32_t value; |
54 | IGNORE_RACES_START (); |
55 | if (delta == 0) { |
56 | value = ATM_LOAD_ACQ (&c->value); |
57 | } else { |
58 | nsync_mu_lock (&c->counter_mu); |
59 | do { |
60 | value = ATM_LOAD (&c->value); |
61 | } while (!ATM_CAS_RELACQ (&c->value, value, value+delta)); |
62 | value += delta; |
63 | if (delta > 0) { |
64 | /* It's illegal to increase the count from zero if |
65 | there has been a waiter. */ |
66 | ASSERT (value != (uint32_t) delta || !ATM_LOAD (&c->waited)); |
67 | ASSERT (value > value - delta); /* Crash on overflow. */ |
68 | } else { |
69 | ASSERT (value < value - delta); /* Crash on overflow. */ |
70 | } |
71 | if (value == 0) { |
72 | nsync_dll_element_ *p; |
73 | while ((p = nsync_dll_first_ (c->waiters)) != NULL) { |
74 | struct nsync_waiter_s *nw = DLL_NSYNC_WAITER (p); |
75 | c->waiters = nsync_dll_remove_ (c->waiters, p); |
76 | ATM_STORE_REL (&nw->waiting, 0); |
77 | nsync_mu_semaphore_v (nw->sem); |
78 | } |
79 | } |
80 | nsync_mu_unlock (&c->counter_mu); |
81 | } |
82 | IGNORE_RACES_END (); |
83 | return (value); |
84 | } |
85 | |
86 | uint32_t nsync_counter_value (nsync_counter c) { |
87 | uint32_t result; |
88 | IGNORE_RACES_START (); |
89 | result = ATM_LOAD_ACQ (&c->value); |
90 | IGNORE_RACES_END (); |
91 | return (result); |
92 | } |
93 | |
94 | uint32_t nsync_counter_wait (nsync_counter c, nsync_time abs_deadline) { |
95 | struct nsync_waitable_s waitable; |
96 | struct nsync_waitable_s *pwaitable = &waitable; |
97 | uint32_t result = 0; |
98 | waitable.v = c; |
99 | waitable.funcs = &nsync_counter_waitable_funcs; |
100 | if (nsync_wait_n (NULL, NULL, NULL, abs_deadline, 1, &pwaitable) != 0) { |
101 | IGNORE_RACES_START (); |
102 | result = ATM_LOAD_ACQ (&c->value); |
103 | IGNORE_RACES_END (); |
104 | } |
105 | return (result); |
106 | } |
107 | |
108 | static nsync_time counter_ready_time (void *v, struct nsync_waiter_s *nw UNUSED) { |
109 | nsync_counter c = (nsync_counter) v; |
110 | nsync_time r; |
111 | ATM_STORE (&c->waited, 1); |
112 | r = (ATM_LOAD_ACQ (&c->value) == 0? nsync_time_zero : nsync_time_no_deadline); |
113 | return (r); |
114 | } |
115 | |
116 | static int counter_enqueue (void *v, struct nsync_waiter_s *nw) { |
117 | nsync_counter c = (nsync_counter) v; |
118 | int32_t value; |
119 | nsync_mu_lock (&c->counter_mu); |
120 | value = ATM_LOAD_ACQ (&c->value); |
121 | if (value != 0) { |
122 | c->waiters = nsync_dll_make_last_in_list_ (c->waiters, &nw->q); |
123 | ATM_STORE (&nw->waiting, 1); |
124 | } else { |
125 | ATM_STORE (&nw->waiting, 0); |
126 | } |
127 | nsync_mu_unlock (&c->counter_mu); |
128 | return (value != 0); |
129 | } |
130 | |
131 | static int counter_dequeue (void *v, struct nsync_waiter_s *nw) { |
132 | nsync_counter c = (nsync_counter) v; |
133 | int32_t value; |
134 | nsync_mu_lock (&c->counter_mu); |
135 | value = ATM_LOAD_ACQ (&c->value); |
136 | if (ATM_LOAD_ACQ (&nw->waiting) != 0) { |
137 | c->waiters = nsync_dll_remove_ (c->waiters, &nw->q); |
138 | ATM_STORE (&nw->waiting, 0); |
139 | } |
140 | nsync_mu_unlock (&c->counter_mu); |
141 | return (value != 0); |
142 | } |
143 | |
144 | const struct nsync_waitable_funcs_s nsync_counter_waitable_funcs = { |
145 | &counter_ready_time, |
146 | &counter_enqueue, |
147 | &counter_dequeue |
148 | }; |
149 | |
150 | NSYNC_CPP_END_ |
151 | |