Forcing a 32-bit build for Sparcv9 (typical for Sparc v9)
* CFLAGS="-m32 -Wa,-Av9a -g -O2" ./configure
+
ARCHITECTURES SUPPORTED
-----------------------
-Currently, x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64, S390, S390x,
-ARM, Alpha, ia64 and Sparcv9 32/64 are supported. Only tested on Linux so
-far, but should theoretically work on other operating systems.
+Currently, Linux x86 (i386, i486, i586, i686), x86 64-bit, PowerPC 32/64,
+S390, S390x, ARM, MIPS, Alpha, ia64 and Sparcv9 32/64 are supported.
+Tested on Linux, FreeBSD 8.2/8.3/9.0/9.1/10.0 i386/amd64, and Cygwin.
+Should also work on: Android, NetBSD 5, OpenBSD, Darwin (more testing
+needed before claiming support for these OS).
-ARM depends on running a Linux kernel 2.6.15 or better.
+Linux ARM depends on running a Linux kernel 2.6.15 or better, GCC 4.4 or
+better.
The gcc compiler versions 3.3, 3.4, 4.0, 4.1, 4.2, 4.3, 4.4 and 4.5 are
supported, with the following exceptions:
http://www.mail-archive.com/gcc-bugs@gcc.gnu.org/msg281255.html
- gcc 3.3 cannot match the "xchg" instruction on 32-bit x86 build.
See: http://kerneltrap.org/node/7507
-- Alpha, ia64 and ARM architectures depend on 4.x gcc with atomic builtins
- support.
+- Alpha, ia64 and ARM architectures depend on gcc 4.x with atomic builtins
+ support. For ARM this was introduced with gcc 4.4:
+ http://gcc.gnu.org/gcc-4.4/changes.html
+
+Clang version 3.0 (based on LLVM 3.0) is supported.
+
+Building on MacOS X (Darwin) requires a work-around for processor
+detection:
+ # 32-bit
+ ./configure --build=i686-apple-darwin11
+ # 64-bit
+ ./configure --build=x86_64-apple-darwin11
+
+For developers using the git tree:
+
+This source tree is based on the autotools suite from GNU to simplify
+portability. Here are some things you should have on your system in order to
+compile the git repository tree :
+
+- GNU autotools (automake >=1.10, autoconf >=2.50, autoheader >=2.50)
+ (make sure your system wide "automake" points to a recent version!)
+- GNU Libtool >=2.2
+ (for more information, go to http://www.gnu.org/software/autoconf/)
+
+If you get the tree from the repository, you will need to use the "bootstrap"
+script in the root of the tree. It calls all the GNU tools needed to prepare the
+tree configuration.
+
+Test scripts provided in the tests/ directory of the source tree depend
+on "bash" and the "seq" program.
+
+
+API
+---
+
+See the relevant API documentation files in doc/. The APIs provided by
+Userspace RCU are, by prefix:
+
+- rcu_ : Read-Copy Update (see doc/rcu-api.txt)
+- cmm_ : Concurrent Memory Model
+- caa_ : Concurrent Architecture Abstraction
+- cds_ : Concurrent Data Structures (see doc/cds-api.txt)
+- uatomic_: Userspace Atomic (see doc/uatomic-api.txt)
QUICK START GUIDE
instead of inlines, so your application can link with the library.
* Linking with one of the libraries below is always necessary even for
LGPL and GPL applications.
+ * Define URCU_INLINE_SMALL_FUNCTIONS before including Userspace RCU
+ headers if you want Userspace RCU to inline small functions (10
+ lines or less) into the application. It can be used by applications
+ distributed under any kind of license, and does *not* make the
+ application a derived work of Userspace RCU.
+
+ Those small inlined functions are guaranteed to match the library
+ content as long as the library major version is unchanged.
+ Therefore, the application *must* be compiled with headers matching
+ the library major version number. Applications using
+ URCU_INLINE_SMALL_FUNCTIONS may be unable to use debugging
+ features of Userspace RCU without being recompiled.
+
Usage of liburcu
grace periods. A number of additional functions are provided
to manage the helper threads used by call_rcu(), but reasonable
defaults are used if these additional functions are not invoked.
- See API.txt for more details.
+ See rcu-api.txt in userspace-rcu documentation for more details.
Being careful with signals
signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
library do not require any signal.
- Read-side critical sections are allowed in a signal handler with
- liburcu and liburcu-mb. Be careful, however, to disable these signals
+ Read-side critical sections are allowed in a signal handler,
+ except those setup with sigaltstack(2), with liburcu and
+ liburcu-mb. Be careful, however, to disable these signals
between thread creation and calls to rcu_register_thread(), because a
- signal handler nesting on an unregistered thread would not be allowed to
- call rcu_read_lock().
+ signal handler nesting on an unregistered thread would not be
+ allowed to call rcu_read_lock().
Read-side critical sections are _not_ allowed in a signal handler with
liburcu-qsbr, unless signals are disabled explicitly around each
mutex in its dependency chain) should not be acquired from within a RCU
read-side critical section.
+ This is especially important to understand in the context of the
+ QSBR flavor: a registered reader thread being "online" by
+ default should be considered as within a RCU read-side critical
+ section unless explicitly put "offline". Therefore, if
+ synchronize_rcu() is called with a mutex held, this mutex, as
+ well as any mutex which has this mutex in its dependency chain
+ should only be taken when the RCU reader thread is "offline"
+ (this can be performed by calling rcu_thread_offline()).
+
+Interaction with fork()
+
+ Special care must be taken for applications performing fork() without
+ any following exec(). This is caused by the fact that Linux only clones
+ the thread calling fork(), and thus never replicates any of the other
+ parent thread into the child process. Most liburcu implementations
+ require that all registrations (as reader, defer_rcu and call_rcu
+ threads) should be released before a fork() is performed, except for the
+ rather common scenario where fork() is immediately followed by exec() in
+ the child process. The only implementation not subject to that rule is
+ liburcu-bp, which is designed to handle fork() by calling
+ rcu_bp_before_fork, rcu_bp_after_fork_parent and
+ rcu_bp_after_fork_child.
+
+ Applications that use call_rcu() and that fork() without
+ doing an immediate exec() must take special action. The parent
+ must invoke call_rcu_before_fork() before the fork() and
+ call_rcu_after_fork_parent() after the fork(). The child
+ process must invoke call_rcu_after_fork_child().
+ Even though these three APIs are suitable for passing to
+ pthread_atfork(), use of pthread_atfork() is *STRONGLY
+ DISCOURAGED* for programs calling the glibc memory allocator
+ (malloc(), calloc(), free(), ...) within call_rcu callbacks.
+ This is due to limitations in the way glibc memory allocator
+ handles calls to the memory allocator from concurrent threads
+ while the pthread_atfork() handlers are executing.
+ Combining e.g.:
+ * call to free() from callbacks executed within call_rcu worker
+ threads,
+ * executing call_rcu atfork handlers within the glibc pthread
+ atfork mechanism,
+ will sometimes trigger interesting process hangs. This usually
+ hangs on a memory allocator lock within glibc.
+
+Thread Local Storage (TLS)
+
+ Userspace RCU can fall back on pthread_getspecific() to emulate
+ TLS variables on systems where it is not available. This behavior
+ can be forced by specifying --disable-compiler-tls as configure
+ argument.
+
Usage of DEBUG_RCU
DEBUG_RCU is used to add internal debugging self-checks to the
theoretically yielding slightly better performance.
-Interaction with fork()
+MAKE TARGETS
+------------
- Special care must be taken for applications performing fork() without
- any following exec(). This is caused by the fact that Linux only clones
- the thread calling fork(), and thus never replicates any of the other
- parent thread into the child process. Most liburcu implementations
- require that all registrations (as reader, defer_rcu and call_rcu
- threads) should be released before a fork() is performed, except for the
- rather common scenario where fork() is immediately followed by exec() in
- the child process. The only implementation not subject to that rule is
- liburcu-bp, which is designed to handle fork() by calling
- rcu_bp_before_fork, rcu_bp_after_fork_parent and
- rcu_bp_after_fork_child.
+In addition to the usual "make check" target, Userspace RCU features
+"make regtest" and "make bench" targets.
- Applications that use call_rcu() and that fork() without
- doing an immediate exec() must take special action. The parent
- must invoke call_rcu_before_fork() before the fork() and
- call_rcu_after_fork_parent() after the fork(). The child
- process must invoke call_rcu_after_fork_child().
- These three APIs are suitable for passing to pthread_atfork().
+make check: Short tests, meant to be run when rebuilding or porting
+ Userspace RCU.
+
+make regtest: Long (many hours) test, meant to be run when modifying
+ Userspace RCU or porting it to a new architecture or
+ operating system.
+
+make bench: Long (many hours) benchmarks.
+
+CONTACTS
+--------
+
+You can contact the maintainers on the following mailing list:
+lttng-dev@lists.lttng.org
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