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                 Forcing a 32-bit build for Sparcv9 (typical for Sparc v9)
  22                 * CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure
  23
  24 ARCHITECTURES SUPPORTED
  25 -----------------------
  26
  27 Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x
  28 and Sparcv9 32/64 are supported. Only tested on Linux so far, but should
  29 theoretically work on other operating systems.
  30
  31 QUICK START GUIDE
  32 -----------------
  33
  34 Usage of all urcu libraries
  35
  36         * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
  37           before including the urcu.h or urcu-qsbr.h header. If your application
  38           is distributed under another license, function calls will be generated
  39           instead of inlines, so your application can link with the library.
  40         * Linking with one of the libraries below is always necessary even for
  41           LGPL and GPL applications.
  42
  43 Usage of liburcu
  44
  45         * #include <urcu.h>
  46         * Link the application with "-lurcu".
  47         * This is the preferred version of the library, both in terms of speed
  48           and flexibility. Requires a signal, typically SIGUSR1. Can be
  49           overridden with -DSIGURCU by modifying Makefile.build.inc.
  50
  51 Usage of liburcu-mb
  52
  53         * #include <urcu.h>
  54         * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB".
  55         * Link with "-lurcu-mb".
  56         * This version of the urcu library does not need to
  57           reserve a signal number. URCU_MB uses full memory barriers for
  58           readers. This eliminates the need for signals but results in slower
  59           reads.
  60
  61 Usage of liburcu-qsbr
  62
  63         * #include <urcu-qsbr.h>
  64         * Link with "-lurcu-qsbr".
  65         * The QSBR flavor of RCU needs to have each reader thread executing
  66           rcu_quiescent_state() periodically to progress. rcu_thread_online()
  67           and rcu_thread_offline() can be used to mark long periods for which
  68           the threads are not active. It provides the fastest read-side at the
  69           expense of more intrusiveness in the application code.
  70
  71 Usage of liburcu-bp
  72
  73         * #include <urcu-bp.h>
  74         * Link with "-lurcu-bp".
  75         * The BP library flavor stands for "bulletproof". It is specifically
  76           designed to help tracing library to hook on applications without
  77           requiring to modify these applications. urcu_init(),
  78           rcu_register_thread() and rcu_unregister_thread() all become nops.
  79           The state is dealt with by the library internally at the expense of
  80           read-side and write-side performance.
  81
  82 Initialization
  83
  84         Each thread that has reader critical sections (that uses
  85         rcu_read_lock()/rcu_read_unlock() must first register to the URCU
  86         library. This is done by calling rcu_register_thread(). Unregistration
  87         must be performed before exiting the thread by using
  88         rcu_unregister_thread().
  89
  90 Reading
  91
  92         Reader critical sections must be protected by locating them between
  93         calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
  94         rcu_dereference() may be called to read an RCU protected pointer.
  95
  96 Writing
  97
  98         rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
  99         After, synchronize_rcu() must be called. When it returns, the old
 100         values are not in usage anymore.
 101
 102 Usage of liburcu-defer
 103
 104         * #include <urcu-defer.h>
 105         * Link with "-lurcu-defer", and also with one of the urcu library
 106           (either urcu, urcu-bp, urcu-mb or urcu-qsbr).
 107         * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
 108           callbacks are executed in batch periodically after a grace period.
 109           Do _not_ use defer_rcu() within a read-side critical section, because
 110           it may call synchronize_rcu() if the thread queue is full.
 111         * Provides defer_rcu_ratelimit() primitive, which acts just like
 112           defer_rcu(), but takes an additional rate limiter callback forcing
 113           synchronized callback execution of the limiter returns non-zero.
 114         * Requires that rcu_defer_barrier() must be called in library destructor
 115           if a library queues callbacks and is expected to be unloaded with
 116           dlclose().
 117         * Its API is currently experimental. It may change in future library
 118           releases.
 119
 120 Being careful with signals
 121
 122         The liburcu library uses signals internally. The signal handler is
 123         registered with the SA_RESTART flag. However, these signals may cause
 124         some non-restartable system calls to fail with errno = EINTR. Care
 125         should be taken to restart system calls manually if they fail with this
 126         error. A list of non-restartable system calls may be found in
 127         signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
 128         library do not require any signal.
 129
 130         Read-side critical sections are allowed in a signal handler with
 131         liburcu and liburcu-mb. Be careful, however, to disable these signals
 132         between thread creation and calls to rcu_register_thread(), because a
 133         signal handler nesting on an unregistered thread would not be allowed to
 134         call rcu_read_lock().
 135
 136         Read-side critical sections are _not_ allowed in a signal handler with
 137         liburcu-qsbr, unless signals are disabled explicitly around each
 138         rcu_quiescent_state() calls, when threads are put offline and around
 139         calls to synchronize_rcu(). Even then, we do not recommend it.
 140
 141 Usage of DEBUG_RCU
 142
 143         DEBUG_RCU is used to add internal debugging self-checks to the
 144         RCU library. This define adds a performance penalty when enabled.
 145         Can be enabled by uncommenting the corresponding line in
 146         Makefile.build.inc.
 147
 148 Usage of DEBUG_YIELD
 149
 150         DEBUG_YIELD is used to add random delays in the code for testing
 151         purposes.
 152
 153 SMP support
 154
 155         By default the library is configured to use synchronization primitives
 156         adequate for SMP systems. On uniprocessor systems, support for SMP
 157         systems can be disabled with:
 158
 159                 ./configure --disable-smp-support
 160
 161         theoretically yielding slightly better performance.