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