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