X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=README;h=0f92ac690f1ce884139b18557cea062e893abc80;hp=d47e5df9465070010a15797671ed48195dcf0628;hb=7d413817f09b2d17b1a79ea012590609ffab5eb6;hpb=6991f61a6a02d95a4275bcc90aa9bb7037a9e69e diff --git a/README b/README index d47e5df..0f92ac6 100644 --- a/README +++ b/README @@ -1,11 +1,150 @@ -build instructions for userspace-rcu library : +Userspace RCU Implementation +by Mathieu Desnoyers and Paul E. McKenney -make pthreads-x86 -or -make pthreads-ppc +BUILDING +-------- -make -make install + ./bootstrap (skip if using tarball) + ./configure + make + make install + Hints: Forcing 32-bit build: + * CFLAGS=-m32 ./configure - Mathieu Desnoyers + Forcing 64-bit build: + * CFLAGS=-m64 ./configure + + Forcing a 32-bit build with down to 386 compatibility: + * CFLAGS=-m32 ./configure --target=i386-pc-linux-gnu + +ARCHITECTURES SUPPORTED +----------------------- + +Currently, x86 (i386, i486, i586, i686), x86 64, PowerPC 32/64 and S390 are +supported. The current use of sys_futex() makes it Linux-dependent, although +this portability limitation might go away in a near future by using the pthread +cond vars. + +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 + * 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 + * Compile any _LGPL_SOURCE code using this library 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 + * 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. + +Usage of liburcu-bp + + * #include + * Link with "-lurcu-bp". + * The BP library flavor stands for "bulletproof". It is specifically + designed to help tracing library to hook on applications without + requiring to modify these applications. urcu_init(), + rcu_register_thread() and rcu_unregister_thread() all become nops. + The state is dealt with by the library internally at the expense of + read-side and write-side performance. + +Initialization + + Each thread that has reader critical sections (that uses + rcu_read_lock()/rcu_read_unlock() must first register to the URCU + library. This is done by calling rcu_register_thread(). Unregistration + must be performed before exiting the thread by using + rcu_unregister_thread(). + +Reading + + Reader critical sections must be protected by locating them between + calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock, + rcu_dereference() may be called to read an RCU protected pointer. + +Writing + + rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere. + After, synchronize_rcu() must be called. When it returns, the old + values are not in usage anymore. + +Usage of liburcu-defer + + * #include + * Link with "-lurcu-defer" + * Provides call_rcu() primitive to enqueue delayed callbacks. Queued + callbacks are executed in batch periodically after a grace period. + Do _not_ use call_rcu() within a read-side critical section, because + it may call synchronize_rcu() if the thread queue is full. + +Being careful with signals + + 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). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU + library do not require any signal. + + 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(). + + 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 penalty when enabled. + Can be enabled by uncommenting the corresponding line in + Makefile.build.inc. + +Usage of DEBUG_YIELD + + DEBUG_YIELD is used to add random delays in the code for testing + purposes. + +SMP support + + By default the library is configured to use synchronization primitives + adequate for SMP systems. On uniprocessor systems, support for SMP + systems can be disabled with: + + ./configure --disable-smp-support + + theoretically yielding slightly better performance.