README

   1 Userspace RCU Implementation
   2 by Mathieu Desnoyers and Paul E. McKenney
   3
   4 BUILDING
   5 --------
   6
   7         make
   8         #force 32-bit build with: make -f Makefile32
   9         #force 64-bit build with: make -f Makefile64
  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 Initialization
  54
  55         Each thread that has reader critical sections (that uses
  56         rcu_read_lock()/rcu_read_unlock() must first register to the URCU
  57         library. This is done by calling rcu_register_thread(). Unregistration
  58         must be performed before exiting the thread by using
  59         rcu_unregister_thread().
  60
  61 Reading
  62
  63         Reader critical sections must be protected by locating them between
  64         calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
  65         rcu_dereference() may be called to read an RCU protected pointer.
  66
  67 Writing
  68
  69         rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
  70         After, synchronize_rcu() must be called. When it returns, the old
  71         values are not in usage anymore.
  72
  73 Usage of liburcu-defer
  74
  75         * #include <urcu-defer.h>
  76         * Link with "-lurcu-defer"
  77         * Provides call_rcu() primitive to enqueue delayed callbacks. Queued
  78           callbacks are executed in batch periodically after a grace period.
  79           Do _not_ use call_rcu() within a read-side critical section, because
  80           it may call synchronize_rcu() if the thread queue is full.
  81
  82 Being careful with signals
  83
  84         The liburcu library uses signals internally. The signal handler is
  85         registered with the SA_RESTART flag. However, these signals may cause
  86         some non-restartable system calls to fail with errno = EINTR. Care
  87         should be taken to restart system calls manually if they fail with this
  88         error. A list of non-restartable system calls may be found in
  89         signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
  90         library do not require any signal.
  91
  92         Read-side critical sections are allowed in a signal handler with
  93         liburcu and liburcu-mb. Be careful, however, to disable these signals
  94         between thread creation and calls to rcu_register_thread(), because a
  95         signal handler nesting on an unregistered thread would not be allowed to
  96         call rcu_read_lock().
  97
  98         Read-side critical sections are _not_ allowed in a signal handler with
  99         liburcu-qsbr, unless signals are disabled explicitly around each
 100         rcu_quiescent_state() calls, when threads are put offline and around
 101         calls to synchronize_rcu(). Even then, we do not recommend it.
 102
 103 Usage of DEBUG_RCU
 104
 105         DEBUG_RCU is used to add internal debugging self-checks to the
 106         RCU library. This define adds a performance penalty when enabled.
 107         Can be enabled by uncommenting the corresponding line in
 108         Makefile.build.inc.
 109
 110 Usage of DEBUG_YIELD
 111
 112         DEBUG_YIELD is used to add random delays in the code for testing
 113         purposes.