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, in terms of
  48           grace-period detection speed, read-side speed and flexibility.
  49           Dynamically detects kernel support for sys_membarrier(). Falls back
  50           on urcu-mb scheme if support is not present, which has slower
  51           read-side.
  52
  53 Usage of liburcu-qsbr
  54
  55         * #include <urcu-qsbr.h>
  56         * Link with "-lurcu-qsbr".
  57         * The QSBR flavor of RCU needs to have each reader thread executing
  58           rcu_quiescent_state() periodically to progress. rcu_thread_online()
  59           and rcu_thread_offline() can be used to mark long periods for which
  60           the threads are not active. It provides the fastest read-side at the
  61           expense of more intrusiveness in the application code.
  62
  63 Usage of liburcu-mb
  64
  65         * #include <urcu.h>
  66         * Compile any _LGPL_SOURCE code using this library with "-DRCU_MB".
  67         * Link with "-lurcu-mb".
  68         * This version of the urcu library uses memory barriers on the writer
  69           and reader sides. This results in faster grace-period detection, but
  70           results in slower reads.
  71
  72 Usage of liburcu-signal
  73
  74         * #include <urcu.h>
  75         * Compile any _LGPL_SOURCE code using this library with "-DRCU_SIGNAL".
  76         * Link the application with "-lurcu-signal".
  77         * Version of the library that requires a signal, typically SIGUSR1. Can
  78           be overridden with -DSIGRCU by modifying Makefile.build.inc.
  79
  80 Usage of liburcu-bp
  81
  82         * #include <urcu-bp.h>
  83         * Link with "-lurcu-bp".
  84         * The BP library flavor stands for "bulletproof". It is specifically
  85           designed to help tracing library to hook on applications without
  86           requiring to modify these applications. rcu_init(),
  87           rcu_register_thread() and rcu_unregister_thread() all become nops.
  88           The state is dealt with by the library internally at the expense of
  89           read-side and write-side performance.
  90
  91 Initialization
  92
  93         Each thread that has reader critical sections (that uses
  94         rcu_read_lock()/rcu_read_unlock() must first register to the URCU
  95         library. This is done by calling rcu_register_thread(). Unregistration
  96         must be performed before exiting the thread by using
  97         rcu_unregister_thread().
  98
  99 Reading
 100
 101         Reader critical sections must be protected by locating them between
 102         calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
 103         rcu_dereference() may be called to read an RCU protected pointer.
 104
 105 Writing
 106
 107         rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
 108         After, synchronize_rcu() must be called. When it returns, the old
 109         values are not in usage anymore.
 110
 111 Usage of liburcu-defer
 112
 113         * #include <urcu-defer.h>
 114         * Link with "-lurcu-defer", and also with one of the urcu library
 115           (either urcu, urcu-bp, urcu-mb or urcu-qsbr).
 116         * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
 117           callbacks are executed in batch periodically after a grace period.
 118           Do _not_ use defer_rcu() within a read-side critical section, because
 119           it may call synchronize_rcu() if the thread queue is full.
 120         * Provides defer_rcu_ratelimit() primitive, which acts just like
 121           defer_rcu(), but takes an additional rate limiter callback forcing
 122           synchronized callback execution of the limiter returns non-zero.
 123         * Requires that rcu_defer_barrier() must be called in library destructor
 124           if a library queues callbacks and is expected to be unloaded with
 125           dlclose().
 126         * Its API is currently experimental. It may change in future library
 127           releases.
 128
 129 Being careful with signals
 130
 131         The liburcu library uses signals internally. The signal handler is
 132         registered with the SA_RESTART flag. However, these signals may cause
 133         some non-restartable system calls to fail with errno = EINTR. Care
 134         should be taken to restart system calls manually if they fail with this
 135         error. A list of non-restartable system calls may be found in
 136         signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
 137         library do not require any signal.
 138
 139         Read-side critical sections are allowed in a signal handler with
 140         liburcu and liburcu-mb. Be careful, however, to disable these signals
 141         between thread creation and calls to rcu_register_thread(), because a
 142         signal handler nesting on an unregistered thread would not be allowed to
 143         call rcu_read_lock().
 144
 145         Read-side critical sections are _not_ allowed in a signal handler with
 146         liburcu-qsbr, unless signals are disabled explicitly around each
 147         rcu_quiescent_state() calls, when threads are put offline and around
 148         calls to synchronize_rcu(). Even then, we do not recommend it.
 149
 150 Interaction with mutexes
 151
 152         One must be careful to do not cause deadlocks due to interaction of
 153         synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu()
 154         is called with a mutex held, this mutex (or any mutex which has this
 155         mutex in its dependency chain) should not be acquired from within a RCU
 156         read-side critical section.
 157
 158 Usage of DEBUG_RCU
 159
 160         DEBUG_RCU is used to add internal debugging self-checks to the
 161         RCU library. This define adds a performance penalty when enabled.
 162         Can be enabled by uncommenting the corresponding line in
 163         Makefile.build.inc.
 164
 165 Usage of DEBUG_YIELD
 166
 167         DEBUG_YIELD is used to add random delays in the code for testing
 168         purposes.
 169
 170 SMP support
 171
 172         By default the library is configured to use synchronization primitives
 173         adequate for SMP systems. On uniprocessor systems, support for SMP
 174         systems can be disabled with:
 175
 176                 ./configure --disable-smp-support
 177
 178         theoretically yielding slightly better performance.