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