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         Note:   Forcing 32-bit build:
  13                 * CFLAGS=-m32 ./configure
  14
  15                 Forcing 64-bit build:
  16                 * CFLAGS=-m64 ./configure
  17
  18 ARCHITECTURES SUPPORTED
  19 -----------------------
  20
  21 Currently, x86 (only P6+), x86 64, PowerPC 32/64 and S390 are
  22 supported. The current use of sys_futex() makes it Linux-dependent, although
  23 this portability limitation might go away in a near future by using the pthread
  24 cond vars. Also, the restriction against i386, i486 and Pentium might go away if
  25 we integrate some of glibc runtime CPU-detection tests.
  26
  27 QUICK START GUIDE
  28 -----------------
  29
  30 Usage of all urcu libraries
  31
  32         * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
  33           before including the urcu.h or urcu-qsbr.h header. If your application
  34           is distributed under another license, function calls will be generated
  35           instead of inlines, so your application can link with the library.
  36         * Linking with one of the libraries below is always necessary even for
  37           LGPL and GPL applications.
  38
  39 Usage of liburcu
  40
  41         * #include <urcu.h>
  42         * Link the application with "-lurcu".
  43         * This is the preferred version of the library, both in terms of speed
  44           and flexibility. Requires a signal, typically SIGUSR1. Can be
  45           overridden with -DSIGURCU by modifying Makefile.build.inc.
  46
  47 Usage of liburcu-mb
  48
  49         * #include <urcu.h>
  50         * Compile any _LGPL_SOURCE code using this library with "-DURCU_MB".
  51         * Link with "-lurcu-mb".
  52         * This version of the urcu library does not need to
  53           reserve a signal number. URCU_MB uses full memory barriers for
  54           readers. This eliminates the need for signals but results in slower
  55           reads.
  56
  57 Usage of liburcu-qsbr
  58
  59         * #include <urcu-qsbr.h>
  60         * Link with "-lurcu-qsbr".
  61         * The QSBR flavor of RCU needs to have each reader thread executing
  62           rcu_quiescent_state() periodically to progress. rcu_thread_online()
  63           and rcu_thread_offline() can be used to mark long periods for which
  64           the threads are not active. It provides the fastest read-side at the
  65           expense of more intrusiveness in the application code.
  66
  67 Usage of liburcu-bp
  68
  69         * #include <urcu-bp.h>
  70         * Link with "-lurcu-bp".
  71         * The BP library flavor stands for "bulletproof". It is specifically
  72           designed to help tracing library to hook on applications without
  73           requiring to modify these applications. urcu_init(),
  74           rcu_register_thread() and rcu_unregister_thread() all become nops.
  75           The state is dealt with by the library internally at the expense of
  76           read-side and write-side performance.
  77
  78 Initialization
  79
  80         Each thread that has reader critical sections (that uses
  81         rcu_read_lock()/rcu_read_unlock() must first register to the URCU
  82         library. This is done by calling rcu_register_thread(). Unregistration
  83         must be performed before exiting the thread by using
  84         rcu_unregister_thread().
  85
  86 Reading
  87
  88         Reader critical sections must be protected by locating them between
  89         calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
  90         rcu_dereference() may be called to read an RCU protected pointer.
  91
  92 Writing
  93
  94         rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
  95         After, synchronize_rcu() must be called. When it returns, the old
  96         values are not in usage anymore.
  97
  98 Usage of liburcu-defer
  99
 100         * #include <urcu-defer.h>
 101         * Link with "-lurcu-defer"
 102         * Provides call_rcu() primitive to enqueue delayed callbacks. Queued
 103           callbacks are executed in batch periodically after a grace period.
 104           Do _not_ use call_rcu() within a read-side critical section, because
 105           it may call synchronize_rcu() if the thread queue is full.
 106
 107 Being careful with signals
 108
 109         The liburcu library uses signals internally. The signal handler is
 110         registered with the SA_RESTART flag. However, these signals may cause
 111         some non-restartable system calls to fail with errno = EINTR. Care
 112         should be taken to restart system calls manually if they fail with this
 113         error. A list of non-restartable system calls may be found in
 114         signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
 115         library do not require any signal.
 116
 117         Read-side critical sections are allowed in a signal handler with
 118         liburcu and liburcu-mb. Be careful, however, to disable these signals
 119         between thread creation and calls to rcu_register_thread(), because a
 120         signal handler nesting on an unregistered thread would not be allowed to
 121         call rcu_read_lock().
 122
 123         Read-side critical sections are _not_ allowed in a signal handler with
 124         liburcu-qsbr, unless signals are disabled explicitly around each
 125         rcu_quiescent_state() calls, when threads are put offline and around
 126         calls to synchronize_rcu(). Even then, we do not recommend it.
 127
 128 Usage of DEBUG_RCU
 129
 130         DEBUG_RCU is used to add internal debugging self-checks to the
 131         RCU library. This define adds a performance penalty when enabled.
 132         Can be enabled by uncommenting the corresponding line in
 133         Makefile.build.inc.
 134
 135 Usage of DEBUG_YIELD
 136
 137         DEBUG_YIELD is used to add random delays in the code for testing
 138         purposes.