1 /* 2 * Copyright (C) 2008 The Android Open Source Project 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in 12 * the documentation and/or other materials provided with the 13 * distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS 22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include <errno.h> 30 #include <pthread.h> 31 #include <stdatomic.h> 32 33 #include "private/bionic_tls.h" 34 #include "pthread_internal.h" 35 36 typedef void (*key_destructor_t)(void*); 37 38 #define SEQ_KEY_IN_USE_BIT 0 39 40 #define SEQ_INCREMENT_STEP (1 << SEQ_KEY_IN_USE_BIT) 41 42 // pthread_key_internal_t records the use of each pthread key slot: 43 // seq records the state of the slot. 44 // bit 0 is 1 when the key is in use, 0 when it is unused. Each time we create or delete the 45 // pthread key in the slot, we increse the seq by 1 (which inverts bit 0). The reason to use 46 // a sequence number instead of a boolean value here is that when the key slot is deleted and 47 // reused for a new key, pthread_getspecific will not return stale data. 48 // key_destructor records the destructor called at thread exit. 49 struct pthread_key_internal_t { 50 atomic_uintptr_t seq; 51 atomic_uintptr_t key_destructor; 52 }; 53 54 static pthread_key_internal_t key_map[BIONIC_PTHREAD_KEY_COUNT]; 55 56 static inline bool SeqOfKeyInUse(uintptr_t seq) { 57 return seq & (1 << SEQ_KEY_IN_USE_BIT); 58 } 59 60 #define KEY_VALID_FLAG (1 << 31) 61 62 static_assert(sizeof(pthread_key_t) == sizeof(int) && static_cast<pthread_key_t>(-1) < 0, 63 "pthread_key_t should be typedef to int"); 64 65 static inline bool KeyInValidRange(pthread_key_t key) { 66 // key < 0 means bit 31 is set. 67 // Then key < (2^31 | BIONIC_PTHREAD_KEY_COUNT) means the index part of key < BIONIC_PTHREAD_KEY_COUNT. 68 return (key < (KEY_VALID_FLAG | BIONIC_PTHREAD_KEY_COUNT)); 69 } 70 71 // Called from pthread_exit() to remove all pthread keys. This must call the destructor of 72 // all keys that have a non-NULL data value and a non-NULL destructor. 73 __LIBC_HIDDEN__ void pthread_key_clean_all() { 74 // Because destructors can do funky things like deleting/creating other keys, 75 // we need to implement this in a loop. 76 pthread_key_data_t* key_data = __get_thread()->key_data; 77 for (size_t rounds = PTHREAD_DESTRUCTOR_ITERATIONS; rounds > 0; --rounds) { 78 size_t called_destructor_count = 0; 79 for (size_t i = 0; i < BIONIC_PTHREAD_KEY_COUNT; ++i) { 80 uintptr_t seq = atomic_load_explicit(&key_map[i].seq, memory_order_relaxed); 81 if (SeqOfKeyInUse(seq) && seq == key_data[i].seq && key_data[i].data != NULL) { 82 // Other threads may be calling pthread_key_delete/pthread_key_create while current thread 83 // is exiting. So we need to ensure we read the right key_destructor. 84 // We can rely on a user-established happens-before relationship between the creation and 85 // use of pthread key to ensure that we're not getting an earlier key_destructor. 86 // To avoid using the key_destructor of the newly created key in the same slot, we need to 87 // recheck the sequence number after reading key_destructor. As a result, we either see the 88 // right key_destructor, or the sequence number must have changed when we reread it below. 89 key_destructor_t key_destructor = reinterpret_cast<key_destructor_t>( 90 atomic_load_explicit(&key_map[i].key_destructor, memory_order_relaxed)); 91 if (key_destructor == NULL) { 92 continue; 93 } 94 atomic_thread_fence(memory_order_acquire); 95 if (atomic_load_explicit(&key_map[i].seq, memory_order_relaxed) != seq) { 96 continue; 97 } 98 99 // We need to clear the key data now, this will prevent the destructor (or a later one) 100 // from seeing the old value if it calls pthread_getspecific(). 101 // We don't do this if 'key_destructor == NULL' just in case another destructor 102 // function is responsible for manually releasing the corresponding data. 103 void* data = key_data[i].data; 104 key_data[i].data = NULL; 105 106 (*key_destructor)(data); 107 ++called_destructor_count; 108 } 109 } 110 111 // If we didn't call any destructors, there is no need to check the pthread keys again. 112 if (called_destructor_count == 0) { 113 break; 114 } 115 } 116 } 117 118 int pthread_key_create(pthread_key_t* key, void (*key_destructor)(void*)) { 119 for (size_t i = 0; i < BIONIC_PTHREAD_KEY_COUNT; ++i) { 120 uintptr_t seq = atomic_load_explicit(&key_map[i].seq, memory_order_relaxed); 121 while (!SeqOfKeyInUse(seq)) { 122 if (atomic_compare_exchange_weak(&key_map[i].seq, &seq, seq + SEQ_INCREMENT_STEP)) { 123 atomic_store(&key_map[i].key_destructor, reinterpret_cast<uintptr_t>(key_destructor)); 124 *key = i | KEY_VALID_FLAG; 125 return 0; 126 } 127 } 128 } 129 return EAGAIN; 130 } 131 132 // Deletes a pthread_key_t. note that the standard mandates that this does 133 // not call the destructors for non-NULL key values. Instead, it is the 134 // responsibility of the caller to properly dispose of the corresponding data 135 // and resources, using any means it finds suitable. 136 int pthread_key_delete(pthread_key_t key) { 137 if (__predict_false(!KeyInValidRange(key))) { 138 return EINVAL; 139 } 140 key &= ~KEY_VALID_FLAG; 141 // Increase seq to invalidate values in all threads. 142 uintptr_t seq = atomic_load_explicit(&key_map[key].seq, memory_order_relaxed); 143 if (SeqOfKeyInUse(seq)) { 144 if (atomic_compare_exchange_strong(&key_map[key].seq, &seq, seq + SEQ_INCREMENT_STEP)) { 145 return 0; 146 } 147 } 148 return EINVAL; 149 } 150 151 void* pthread_getspecific(pthread_key_t key) { 152 if (__predict_false(!KeyInValidRange(key))) { 153 return NULL; 154 } 155 key &= ~KEY_VALID_FLAG; 156 uintptr_t seq = atomic_load_explicit(&key_map[key].seq, memory_order_relaxed); 157 pthread_key_data_t* data = &(__get_thread()->key_data[key]); 158 // It is user's responsibility to synchornize between the creation and use of pthread keys, 159 // so we use memory_order_relaxed when checking the sequence number. 160 if (__predict_true(SeqOfKeyInUse(seq) && data->seq == seq)) { 161 return data->data; 162 } 163 // We arrive here when current thread holds the seq of an deleted pthread key. So the 164 // data is for the deleted pthread key, and should be cleared. 165 data->data = NULL; 166 return NULL; 167 } 168 169 int pthread_setspecific(pthread_key_t key, const void* ptr) { 170 if (__predict_false(!KeyInValidRange(key))) { 171 return EINVAL; 172 } 173 key &= ~KEY_VALID_FLAG; 174 uintptr_t seq = atomic_load_explicit(&key_map[key].seq, memory_order_relaxed); 175 if (__predict_true(SeqOfKeyInUse(seq))) { 176 pthread_key_data_t* data = &(__get_thread()->key_data[key]); 177 data->seq = seq; 178 data->data = const_cast<void*>(ptr); 179 return 0; 180 } 181 return EINVAL; 182 } 183
