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 -g -O2" ./configure
  14
  15                 Forcing 64-bit build:
  16                 * CFLAGS="-m64 -g -O2" ./configure
  17
  18                 Forcing a 32-bit build with 386 backward compatibility:
  19                 * CFLAGS="-m32 -g -O2" ./configure --host=i386-pc-linux-gnu
  20
  21                 Forcing a 32-bit build for Sparcv9 (typical for Sparc v9)
  22                 * CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure
  23
  24 ARCHITECTURES SUPPORTED
  25 -----------------------
  26
  27 Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x
  28 and Sparcv9 32/64 are supported. Only tested on Linux so far, but should
  29 theoretically work on other operating systems.
  30
  31 Alpha and ia64 architectures are supported, but depend on 4.x gcc with atomic
  32 builtins support.
  33
  34 QUICK START GUIDE
  35 -----------------
  36
  37 Usage of all urcu libraries
  38
  39         * Define _LGPL_SOURCE (only) if your code is LGPL or GPL compatible
  40           before including the urcu.h or urcu-qsbr.h header. If your application
  41           is distributed under another license, function calls will be generated
  42           instead of inlines, so your application can link with the library.
  43         * Linking with one of the libraries below is always necessary even for
  44           LGPL and GPL applications.
  45
  46 Usage of liburcu
  47
  48         * #include <urcu.h>
  49         * Link the application with "-lurcu".
  50         * This is the preferred version of the library, in terms of
  51           grace-period detection speed, read-side speed and flexibility.
  52           Dynamically detects kernel support for sys_membarrier(). Falls back
  53           on urcu-mb scheme if support is not present, which has slower
  54           read-side.
  55
  56 Usage of liburcu-qsbr
  57
  58         * #include <urcu-qsbr.h>
  59         * Link with "-lurcu-qsbr".
  60         * The QSBR flavor of RCU needs to have each reader thread executing
  61           rcu_quiescent_state() periodically to progress. rcu_thread_online()
  62           and rcu_thread_offline() can be used to mark long periods for which
  63           the threads are not active. It provides the fastest read-side at the
  64           expense of more intrusiveness in the application code.
  65
  66 Usage of liburcu-mb
  67
  68         * #include <urcu.h>
  69         * Compile any _LGPL_SOURCE code using this library with "-DRCU_MB".
  70         * Link with "-lurcu-mb".
  71         * This version of the urcu library uses memory barriers on the writer
  72           and reader sides. This results in faster grace-period detection, but
  73           results in slower reads.
  74
  75 Usage of liburcu-signal
  76
  77         * #include <urcu.h>
  78         * Compile any _LGPL_SOURCE code using this library with "-DRCU_SIGNAL".
  79         * Link the application with "-lurcu-signal".
  80         * Version of the library that requires a signal, typically SIGUSR1. Can
  81           be overridden with -DSIGRCU by modifying Makefile.build.inc.
  82
  83 Usage of liburcu-bp
  84
  85         * #include <urcu-bp.h>
  86         * Link with "-lurcu-bp".
  87         * The BP library flavor stands for "bulletproof". It is specifically
  88           designed to help tracing library to hook on applications without
  89           requiring to modify these applications. rcu_init(),
  90           rcu_register_thread() and rcu_unregister_thread() all become nops.
  91           The state is dealt with by the library internally at the expense of
  92           read-side and write-side performance.
  93
  94 Initialization
  95
  96         Each thread that has reader critical sections (that uses
  97         rcu_read_lock()/rcu_read_unlock() must first register to the URCU
  98         library. This is done by calling rcu_register_thread(). Unregistration
  99         must be performed before exiting the thread by using
 100         rcu_unregister_thread().
 101
 102 Reading
 103
 104         Reader critical sections must be protected by locating them between
 105         calls to rcu_read_lock() and rcu_read_unlock(). Inside that lock,
 106         rcu_dereference() may be called to read an RCU protected pointer.
 107
 108 Writing
 109
 110         rcu_assign_pointer() and rcu_xchg_pointer() may be called anywhere.
 111         After, synchronize_rcu() must be called. When it returns, the old
 112         values are not in usage anymore.
 113
 114 Usage of liburcu-defer
 115
 116         * #include <urcu-defer.h>
 117         * Link with "-lurcu-defer", and also with one of the urcu library
 118           (either urcu, urcu-bp, urcu-mb or urcu-qsbr).
 119         * Provides defer_rcu() primitive to enqueue delayed callbacks. Queued
 120           callbacks are executed in batch periodically after a grace period.
 121           Do _not_ use defer_rcu() within a read-side critical section, because
 122           it may call synchronize_rcu() if the thread queue is full.
 123         * Provides defer_rcu_ratelimit() primitive, which acts just like
 124           defer_rcu(), but takes an additional rate limiter callback forcing
 125           synchronized callback execution of the limiter returns non-zero.
 126         * Requires that rcu_defer_barrier() must be called in library destructor
 127           if a library queues callbacks and is expected to be unloaded with
 128           dlclose().
 129         * Its API is currently experimental. It may change in future library
 130           releases.
 131
 132 Being careful with signals
 133
 134         The liburcu library uses signals internally. The signal handler is
 135         registered with the SA_RESTART flag. However, these signals may cause
 136         some non-restartable system calls to fail with errno = EINTR. Care
 137         should be taken to restart system calls manually if they fail with this
 138         error. A list of non-restartable system calls may be found in
 139         signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
 140         library do not require any signal.
 141
 142         Read-side critical sections are allowed in a signal handler with
 143         liburcu and liburcu-mb. Be careful, however, to disable these signals
 144         between thread creation and calls to rcu_register_thread(), because a
 145         signal handler nesting on an unregistered thread would not be allowed to
 146         call rcu_read_lock().
 147
 148         Read-side critical sections are _not_ allowed in a signal handler with
 149         liburcu-qsbr, unless signals are disabled explicitly around each
 150         rcu_quiescent_state() calls, when threads are put offline and around
 151         calls to synchronize_rcu(). Even then, we do not recommend it.
 152
 153 Interaction with mutexes
 154
 155         One must be careful to do not cause deadlocks due to interaction of
 156         synchronize_rcu() and RCU read-side with mutexes. If synchronize_rcu()
 157         is called with a mutex held, this mutex (or any mutex which has this
 158         mutex in its dependency chain) should not be acquired from within a RCU
 159         read-side critical section.
 160
 161 Usage of DEBUG_RCU
 162
 163         DEBUG_RCU is used to add internal debugging self-checks to the
 164         RCU library. This define adds a performance penalty when enabled.
 165         Can be enabled by uncommenting the corresponding line in
 166         Makefile.build.inc.
 167
 168 Usage of DEBUG_YIELD
 169
 170         DEBUG_YIELD is used to add random delays in the code for testing
 171         purposes.
 172
 173 SMP support
 174
 175         By default the library is configured to use synchronization primitives
 176         adequate for SMP systems. On uniprocessor systems, support for SMP
 177         systems can be disabled with:
 178
 179                 ./configure --disable-smp-support
 180
 181         theoretically yielding slightly better performance.