README

   1 Userspace RCU Implementation
   2 by Mathieu Desnoyers and Paul E. McKenney
   3
   4 BUILDING
   5 --------
   6
   7         ./bootstrap (skip if using tarball)
   8         ./configure
   9         make
  10         make install
  11
  12         Hints:  Forcing 32-bit build:
  13                 * CFLAGS="-m32 -g -O2" ./configure
  14
  15                 Forcing 64-bit build:
  16                 * CFLAGS="-m64 -g -O2" ./configure
  17
  18                 Forcing a 32-bit build with 386 backward compatibility:
  19                 * CFLAGS="-m32 -g -O2" ./configure --host=i386-pc-linux-gnu
  20
  21 ARCHITECTURES SUPPORTED
  22 -----------------------
  23
  24 Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x
  25 and Sparc64 are supported. Only tested on Linux so far, but should
  26 theoretically work on other operating systems.
  27
  28 QUICK START GUIDE
  29 -----------------
  30
  31 Usage of all urcu libraries
  32
  33         * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
  34           before including the urcu.h or urcu-qsbr.h header. If your application
  35           is distributed under another license, function calls will be generated
  36           instead of inlines, so your application can link with the library.
  37         * Linking with one of the libraries below is always necessary even for
  38           LGPL and GPL applications.
  39
  40 Usage of liburcu
  41
  42         * #include <urcu.h>
  43         * Link the application with "-lurcu".
  44         * This is the preferred version of the library, both in terms of speed
  45           and flexibility. Requires a signal, typically SIGUSR1. Can be
  46           overridden with -DSIGURCU by modifying Makefile.build.inc.
  47
  48 Usage of liburcu-mb
  49
  50         * #include <urcu.h>
  51         * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB".
  52         * Link with "-lurcu-mb".
  53         * This version of the urcu library does not need to
  54           reserve a signal number. URCU_MB uses full memory barriers for
  55           readers. This eliminates the need for signals but results in slower
  56           reads.
  57
  58 Usage of liburcu-qsbr
  59
  60         * #include <urcu-qsbr.h>
  61         * Link with "-lurcu-qsbr".
  62         * The QSBR flavor of RCU needs to have each reader thread executing
  63           rcu_quiescent_state() periodically to progress. rcu_thread_online()
  64           and rcu_thread_offline() can be used to mark long periods for which
  65           the threads are not active. It provides the fastest read-side at the
  66           expense of more intrusiveness in the application code.
  67
  68 Usage of liburcu-bp
  69
  70         * #include <urcu-bp.h>
  71         * Link with "-lurcu-bp".
  72         * The BP library flavor stands for "bulletproof". It is specifically
  73           designed to help tracing library to hook on applications without
  74           requiring to modify these applications. urcu_init(),
  75           rcu_register_thread() and rcu_unregister_thread() all become nops.
  76           The state is dealt with by the library internally at the expense of
  77           read-side and write-side performance.
  78
  79 Initialization
  80
  81         Each thread that has reader critical sections (that uses
  82         rcu_read_lock()/rcu_read_unlock() must first register to the URCU
  83         library. This is done by calling rcu_register_thread(). Unregistration
  84         must be performed before exiting the thread by using
  85         rcu_unregister_thread().
  86
  87 Reading
  88
  89         Reader critical sections must be protected by locating them between
  90         calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
  91         rcu_dereference() may be called to read an RCU protected pointer.
  92
  93 Writing
  94
  95         rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
  96         After, synchronize_rcu() must be called. When it returns, the old
  97         values are not in usage anymore.
  98
  99 Usage of liburcu-defer
 100
 101         * #include <urcu-defer.h>
 102         * Link with "-lurcu-defer"
 103         * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
 104           callbacks are executed in batch periodically after a grace period.
 105           Do _not_ use defer_rcu() within a read-side critical section, because
 106           it may call synchronize_rcu() if the thread queue is full.
 107         * Provides defer_rcu_ratelimit() primitive, which acts just like
 108           defer_rcu(), but takes an additional rate limiter callback forcing
 109           synchronized callback execution of the limiter returns non-zero.
 110         * Requires that rcu_defer_barrier() must be called in library destructor
 111           if a library queues callbacks and is expected to be unloaded with
 112           dlclose().
 113         * Its API is currently experimental. It may change in future library
 114           releases.
 115
 116 Being careful with signals
 117
 118         The liburcu library uses signals internally. The signal handler is
 119         registered with the SA_RESTART flag. However, these signals may cause
 120         some non-restartable system calls to fail with errno = EINTR. Care
 121         should be taken to restart system calls manually if they fail with this
 122         error. A list of non-restartable system calls may be found in
 123         signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
 124         library do not require any signal.
 125
 126         Read-side critical sections are allowed in a signal handler with
 127         liburcu and liburcu-mb. Be careful, however, to disable these signals
 128         between thread creation and calls to rcu_register_thread(), because a
 129         signal handler nesting on an unregistered thread would not be allowed to
 130         call rcu_read_lock().
 131
 132         Read-side critical sections are _not_ allowed in a signal handler with
 133         liburcu-qsbr, unless signals are disabled explicitly around each
 134         rcu_quiescent_state() calls, when threads are put offline and around
 135         calls to synchronize_rcu(). Even then, we do not recommend it.
 136
 137 Usage of DEBUG_RCU
 138
 139         DEBUG_RCU is used to add internal debugging self-checks to the
 140         RCU library. This define adds a performance penalty when enabled.
 141         Can be enabled by uncommenting the corresponding line in
 142         Makefile.build.inc.
 143
 144 Usage of DEBUG_YIELD
 145
 146         DEBUG_YIELD is used to add random delays in the code for testing
 147         purposes.
 148
 149 SMP support
 150
 151         By default the library is configured to use synchronization primitives
 152         adequate for SMP systems. On uniprocessor systems, support for SMP
 153         systems can be disabled with:
 154
 155                 ./configure --disable-smp-support
 156
 157         theoretically yielding slightly better performance.