QUICK START GUIDE
-----------------
+Usage of all urcu libraries
+
+ * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
+ before including the urcu.h or urcu-qsbr.h header. If your application
+ is distributed under another license, function calls will be generated
+ instead of inlines, so your application can link with the library.
+ * Linking with one of the libraries below is always necessary even for
+ LGPL and GPL applications.
+
+Usage of liburcu
+
+ * #include <urcu.h>
+ * Link the application with "-lurcu".
+ * This is the preferred version of the library, both in terms of speed
+ and flexibility. Requires a signal, typically SIGUSR1. Can be
+ overridden with -DSIGURCU by modifying Makefile.build.inc.
+
+Usage of liburcu-mb
+
+ * #include <urcu.h>
+ * Compile code with "-DURCU_MB"
+ * Link with "-lurcu-mb".
+ * This version of the urcu library does not need to
+ reserve a signal number. URCU_MB uses full memory barriers for
+ readers. This eliminates the need for signals but results in slower
+ reads.
+
+Usage of liburcu-qsbr
+
+ * #include <urcu-qsbr.h>
+ * Link with "-lurcu-qsbr".
+ * The QSBR flavor of RCU needs to have each reader thread executing
+ rcu_quiescent_state() periodically to progress. rcu_thread_online()
+ and rcu_thread_offline() can be used to mark long periods for which
+ the threads are not active. It provides the fastest read-side at the
+ expense of more intrusiveness in the application code.
+
Initialization
Each thread that has reader critical sections (that uses
Being careful with signals
- The urcu library uses signals internally. The signal handler is
+ The liburcu library uses signals internally. The signal handler is
registered with the SA_RESTART flag. However, these signals may cause
some non-restartable system calls to fail with errno = EINTR. Care
should be taken to restart system calls manually if they fail with this
error. A list of non-restartable system calls may be found in
- signal(7). To ensure the Userspace RCU library does not use signals,
- see "Usage of liburcu-mb" below.
+ signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
+ library do not require any signal.
- Read-side critical sections can are allowed in a signal handler with
+ Read-side critical sections are allowed in a signal handler with
liburcu and liburcu-mb. Be careful, however, to disable these signals
between thread creation and calls to rcu_register_thread(), because a
signal handler nesting on an unregistered thread would not be allowed to
call rcu_read_lock().
-Usage of liburcu
-
- This is the preferred version of the library, both in terms of speed and
- flexibility. Define _LGPL_SOURCE if your code is LGPL or GPL (otherwise
- function calls will be generated instead of inlines). Use the urcu.h
- header. Link the application with "-lurcu".
-
-Usage of liburcu-mb
-
- Compile code with "-DCONFIG_URCU_AVOID_SIGNALS" and link with
- "-lurcu-mb" to use a version of the urcu library which does not need to
- reserve a signal number. CONFIG_URCU_AVOID_SIGNALS uses full SMP
- barriers for readers. This eliminates the need for signals but results
- in slower reads.
-
-Usage of liburcu-qsbr
-
- The QSBR flavor of RCU needs to have each reader thread executing
- rcu_quiescent_state() periodically to progress. rcu_thread_online() and
- rcu_thread_offline() can be used to mark long periods for which the
- threads are not active. Link with "-lurcu-qsbr" and use urcu-qsbr.h.
+ Read-side critical sections are _not_ allowed in a signal handler with
+ liburcu-qsbr, unless signals are disabled explicitly around each
+ rcu_quiescent_state() calls, when threads are put offline and around
+ calls to synchronize_rcu(). Even then, we do not recommend it.
Usage of DEBUG_RCU
DEBUG_RCU is used to add internal debugging self-checks to the
- RCU library. This define adds a performance penality when enabled.
+ RCU library. This define adds a performance penalty when enabled.
Can be enabled by uncommenting the corresponding line in
Makefile.build.inc.
DEBUG_YIELD is used to add random delays in the code for testing
purposes.
-
-
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#include "urcu.h"
-#ifndef CONFIG_URCU_AVOID_SIGNALS
+#ifndef URCU_MB
void __attribute__((constructor)) urcu_init(void);
void __attribute__((destructor)) urcu_exit(void);
#else
STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
}
-#ifdef CONFIG_URCU_AVOID_SIGNALS
+#ifdef URCU_MB
#ifdef HAS_INCOHERENT_CACHES
static void force_mb_single_thread(struct reader_registry *index)
{
{
smp_mb();
}
-#else /* #ifdef CONFIG_URCU_AVOID_SIGNALS */
+#else /* #ifdef URCU_MB */
#ifdef HAS_INCOHERENT_CACHES
static void force_mb_single_thread(struct reader_registry *index)
{
}
smp_mb(); /* read ->need_mb before ending the barrier */
}
-#endif /* #else #ifdef CONFIG_URCU_AVOID_SIGNALS */
+#endif /* #else #ifdef URCU_MB */
void wait_for_quiescent_state(void)
{
internal_urcu_unlock();
}
-#ifndef CONFIG_URCU_AVOID_SIGNALS
+#ifndef URCU_MB
static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
{
/*
assert(act.sa_sigaction == sigurcu_handler);
free(registry);
}
-#endif /* #ifndef CONFIG_URCU_AVOID_SIGNALS */
+#endif /* #ifndef URCU_MB */
projects / userspace-rcu.git / commitdiff
