1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
|
/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <errno.h>
#include <pthread.h>
#include <stdatomic.h>
#include "private/bionic_tls.h"
#include "pthread_internal.h"
typedef void (*key_destructor_t)(void*);
#define SEQ_KEY_IN_USE_BIT 0
#define SEQ_INCREMENT_STEP (1 << SEQ_KEY_IN_USE_BIT)
// pthread_key_internal_t records the use of each pthread key slot:
// seq records the state of the slot.
// bit 0 is 1 when the key is in use, 0 when it is unused. Each time we create or delete the
// pthread key in the slot, we increse the seq by 1 (which inverts bit 0). The reason to use
// a sequence number instead of a boolean value here is that when the key slot is deleted and
// reused for a new key, pthread_getspecific will not return stale data.
// key_destructor records the destructor called at thread exit.
struct pthread_key_internal_t {
atomic_uintptr_t seq;
atomic_uintptr_t key_destructor;
};
static pthread_key_internal_t key_map[BIONIC_PTHREAD_KEY_COUNT];
static inline bool SeqOfKeyInUse(uintptr_t seq) {
return seq & (1 << SEQ_KEY_IN_USE_BIT);
}
#define KEY_VALID_FLAG (1 << 31)
static_assert(sizeof(pthread_key_t) == sizeof(int) && static_cast<pthread_key_t>(-1) < 0,
"pthread_key_t should be typedef to int");
static inline bool KeyInValidRange(pthread_key_t key) {
// key < 0 means bit 31 is set.
// Then key < (2^31 | BIONIC_PTHREAD_KEY_COUNT) means the index part of key < BIONIC_PTHREAD_KEY_COUNT.
return (key < (KEY_VALID_FLAG | BIONIC_PTHREAD_KEY_COUNT));
}
// Called from pthread_exit() to remove all pthread keys. This must call the destructor of
// all keys that have a non-NULL data value and a non-NULL destructor.
__LIBC_HIDDEN__ void pthread_key_clean_all() {
// Because destructors can do funky things like deleting/creating other keys,
// we need to implement this in a loop.
pthread_key_data_t* key_data = __get_thread()->key_data;
for (size_t rounds = PTHREAD_DESTRUCTOR_ITERATIONS; rounds > 0; --rounds) {
size_t called_destructor_count = 0;
for (size_t i = 0; i < BIONIC_PTHREAD_KEY_COUNT; ++i) {
uintptr_t seq = atomic_load_explicit(&key_map[i].seq, memory_order_relaxed);
if (SeqOfKeyInUse(seq) && seq == key_data[i].seq && key_data[i].data != NULL) {
// Other threads may be calling pthread_key_delete/pthread_key_create while current thread
// is exiting. So we need to ensure we read the right key_destructor.
// We can rely on a user-established happens-before relationship between the creation and
// use of pthread key to ensure that we're not getting an earlier key_destructor.
// To avoid using the key_destructor of the newly created key in the same slot, we need to
// recheck the sequence number after reading key_destructor. As a result, we either see the
// right key_destructor, or the sequence number must have changed when we reread it below.
key_destructor_t key_destructor = reinterpret_cast<key_destructor_t>(
atomic_load_explicit(&key_map[i].key_destructor, memory_order_relaxed));
if (key_destructor == NULL) {
continue;
}
atomic_thread_fence(memory_order_acquire);
if (atomic_load_explicit(&key_map[i].seq, memory_order_relaxed) != seq) {
continue;
}
// We need to clear the key data now, this will prevent the destructor (or a later one)
// from seeing the old value if it calls pthread_getspecific().
// We don't do this if 'key_destructor == NULL' just in case another destructor
// function is responsible for manually releasing the corresponding data.
void* data = key_data[i].data;
key_data[i].data = NULL;
(*key_destructor)(data);
++called_destructor_count;
}
}
// If we didn't call any destructors, there is no need to check the pthread keys again.
if (called_destructor_count == 0) {
break;
}
}
}
int pthread_key_create(pthread_key_t* key, void (*key_destructor)(void*)) {
for (size_t i = 0; i < BIONIC_PTHREAD_KEY_COUNT; ++i) {
uintptr_t seq = atomic_load_explicit(&key_map[i].seq, memory_order_relaxed);
while (!SeqOfKeyInUse(seq)) {
if (atomic_compare_exchange_weak(&key_map[i].seq, &seq, seq + SEQ_INCREMENT_STEP)) {
atomic_store(&key_map[i].key_destructor, reinterpret_cast<uintptr_t>(key_destructor));
*key = i | KEY_VALID_FLAG;
return 0;
}
}
}
return EAGAIN;
}
// Deletes a pthread_key_t. note that the standard mandates that this does
// not call the destructors for non-NULL key values. Instead, it is the
// responsibility of the caller to properly dispose of the corresponding data
// and resources, using any means it finds suitable.
int pthread_key_delete(pthread_key_t key) {
if (__predict_false(!KeyInValidRange(key))) {
return EINVAL;
}
key &= ~KEY_VALID_FLAG;
// Increase seq to invalidate values in all threads.
uintptr_t seq = atomic_load_explicit(&key_map[key].seq, memory_order_relaxed);
if (SeqOfKeyInUse(seq)) {
if (atomic_compare_exchange_strong(&key_map[key].seq, &seq, seq + SEQ_INCREMENT_STEP)) {
return 0;
}
}
return EINVAL;
}
void* pthread_getspecific(pthread_key_t key) {
if (__predict_false(!KeyInValidRange(key))) {
return NULL;
}
key &= ~KEY_VALID_FLAG;
uintptr_t seq = atomic_load_explicit(&key_map[key].seq, memory_order_relaxed);
pthread_key_data_t* data = &(__get_thread()->key_data[key]);
// It is user's responsibility to synchornize between the creation and use of pthread keys,
// so we use memory_order_relaxed when checking the sequence number.
if (__predict_true(SeqOfKeyInUse(seq) && data->seq == seq)) {
return data->data;
}
// We arrive here when current thread holds the seq of an deleted pthread key. So the
// data is for the deleted pthread key, and should be cleared.
data->data = NULL;
return NULL;
}
int pthread_setspecific(pthread_key_t key, const void* ptr) {
if (__predict_false(!KeyInValidRange(key))) {
return EINVAL;
}
key &= ~KEY_VALID_FLAG;
uintptr_t seq = atomic_load_explicit(&key_map[key].seq, memory_order_relaxed);
if (__predict_true(SeqOfKeyInUse(seq))) {
pthread_key_data_t* data = &(__get_thread()->key_data[key]);
data->seq = seq;
data->data = const_cast<void*>(ptr);
return 0;
}
return EINVAL;
}
|
