urcu/tls-compat.h

   1 #ifndef _URCU_TLS_COMPAT_H
   2 #define _URCU_TLS_COMPAT_H
   3
   4 /*
   5  * urcu/tls-compat.h
   6  *
   7  * Userspace RCU library - Thread-Local Storage Compatibility Header
   8  *
   9  * Copyright 2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  10  *
  11  * This library is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU Lesser General Public
  13  * License as published by the Free Software Foundation; either
  14  * version 2.1 of the License, or (at your option) any later version.
  15  *
  16  * This library is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  * Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public
  22  * License along with this library; if not, write to the Free Software
  23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  24  */
  25
  26 #include <stdlib.h>
  27 #include <urcu/config.h>
  28 #include <urcu/compiler.h>
  29 #include <urcu/arch.h>
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 #ifdef CONFIG_RCU_TLS   /* Based on ax_tls.m4 */
  36
  37 /*
  38  * Hint: How to define/declare TLS variables of compound types
  39  *       such as array or function pointers?
  40  *
  41  * Answer: Use typedef to assign a type_name to the compound type.
  42  * Example: Define a TLS variable which is an int array with len=4:
  43  *
  44  *      typedef int my_int_array_type[4];
  45  *      DEFINE_URCU_TLS(my_int_array_type, var_name);
  46  *
  47  * Another example:
  48  *      typedef void (*call_rcu_flavor)(struct rcu_head *, XXXX);
  49  *      DECLARE_URCU_TLS(call_rcu_flavor, p_call_rcu);
  50  *
  51  * NOTE: URCU_TLS() is NOT async-signal-safe, you can't use it
  52  * inside any function which can be called from signal handler.
  53  *
  54  * But if pthread_getspecific() is async-signal-safe in your
  55  * platform, you can make URCU_TLS() async-signal-safe via:
  56  * ensuring the first call to URCU_TLS() of a given TLS variable of
  57  * all threads is called earliest from a non-signal handler function.
  58  *
  59  * Example: In any thread, the first call of URCU_TLS(rcu_reader)
  60  * is called from rcu_register_thread(), so we can ensure all later
  61  * URCU_TLS(rcu_reader) in any thread is async-signal-safe.
  62  *
  63  * Moreover, URCU_TLS variables should not be touched from signal
  64  * handlers setup with with sigaltstack(2).
  65  */
  66
  67 # define DECLARE_URCU_TLS(type, name)   \
  68         CONFIG_RCU_TLS type name
  69
  70 # define DEFINE_URCU_TLS(type, name)    \
  71         CONFIG_RCU_TLS type name
  72
  73 # define URCU_TLS(name)         (name)
  74
  75 #else /* #ifndef CONFIG_RCU_TLS */
  76
  77 # include <pthread.h>
  78
  79 struct urcu_tls {
  80         pthread_key_t key;
  81         pthread_mutex_t init_mutex;
  82         int init_done;
  83 };
  84
  85 # define DECLARE_URCU_TLS(type, name)                           \
  86         type *__tls_access_ ## name(void)
  87
  88 /*
  89  * Note: we don't free memory at process exit, since it will be dealt
  90  * with by the OS.
  91  */
  92 # define DEFINE_URCU_TLS(type, name)                            \
  93         type *__tls_access_ ## name(void)                       \
  94         {                                                       \
  95                 static struct urcu_tls __tls_ ## name = {       \
  96                         .init_mutex = PTHREAD_MUTEX_INITIALIZER,\
  97                         .init_done = 0,                         \
  98                 };                                              \
  99                 void *__tls_p;                                  \
 100                 if (!__tls_ ## name.init_done) {                \
 101                         /* Mutex to protect concurrent init */  \
 102                         pthread_mutex_lock(&__tls_ ## name.init_mutex); \
 103                         if (!__tls_ ## name.init_done) {        \
 104                                 (void) pthread_key_create(&__tls_ ## name.key, \
 105                                         free);                  \
 106                                 cmm_smp_wmb();  /* create key before write init_done */ \
 107                                 __tls_ ## name.init_done = 1;   \
 108                         }                                       \
 109                         pthread_mutex_unlock(&__tls_ ## name.init_mutex); \
 110                 }                                               \
 111                 cmm_smp_rmb();  /* read init_done before getting key */ \
 112                 __tls_p = pthread_getspecific(__tls_ ## name.key); \
 113                 if (caa_unlikely(__tls_p == NULL)) {            \
 114                         __tls_p = calloc(1, sizeof(type));      \
 115                         (void) pthread_setspecific(__tls_ ## name.key,  \
 116                                 __tls_p);                       \
 117                 }                                               \
 118                 return __tls_p;                                 \
 119         }
 120
 121 # define URCU_TLS(name)         (*__tls_access_ ## name())
 122
 123 #endif  /* #else #ifndef CONFIG_RCU_TLS */
 124
 125 #ifdef __cplusplus
 126 }
 127 #endif
 128
 129 #endif /* _URCU_TLS_COMPAT_H */