Currently, the following architectures are supported:
- - Linux x86 (i386, i486, i586, i686)
- - x86 64-bit
+ - x86 (i386, i486, i586, i686)
+ - amd64 / x86_64
- PowerPC 32/64
- S390, S390x
- ARM 32/64
- Sparcv9 32/64
- Tilera
- hppa/PA-RISC
+ - m68k
+ - RISC-V
+
+Tested on:
+
+ - Linux all architectures
+ - FreeBSD 8.2/8.3/9.0/9.1/10.0 i386/amd64
+ - Solaris 10/11 i386
+ - Cygwin i386/amd64
+ - MacOS amd64/arm64
-Tested on Linux, FreeBSD 8.2/8.3/9.0/9.1/10.0 i386/amd64, and Cygwin.
Should also work on:
- Android
- 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.
+ - Linux aarch64 depends on GCC 5.1 or better because prior versions
+ perform unsafe access to deallocated stack.
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)
+ - GNU autotools (automake >=1.12, autoconf >=2.69)
(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/)
`URCU_INLINE_SMALL_FUNCTIONS` may be unable to use debugging
features of Userspace RCU without being recompiled.
+There are multiple flavors of liburcu available:
+
+ - `memb`,
+ - `qsbr`,
+ - `mb`,
+ - `signal`,
+ - `bp`.
-### Usage of `liburcu`
+The API members start with the prefix "urcu_<flavor>_", where
+<flavor> is the chosen flavor name.
- 1. `#include <urcu.h>`
- 2. Link the application with `-lurcu`
+
+### Usage of `liburcu-memb`
+
+ 1. `#include <urcu/urcu-memb.h>`
+ 2. Link the application with `-lurcu-memb`
This is the preferred version of the library, in terms of
grace-period detection speed, read-side speed and flexibility.
### Usage of `liburcu-qsbr`
- 1. `#include <urcu-qsbr.h>`
+ 1. `#include <urcu/urcu-qsbr.h>`
2. Link with `-lurcu-qsbr`
The QSBR flavor of RCU needs to have each reader thread executing
### Usage of `liburcu-mb`
- 1. `#include <urcu.h>`
- 2. Compile any `_LGPL_SOURCE` code using this library with `-DRCU_MB`
- 3. Link with `-lurcu-mb`
+ 1. `#include <urcu/urcu-mb.h>`
+ 2. Link with `-lurcu-mb`
This version of the urcu library uses memory barriers on the writer
and reader sides. This results in faster grace-period detection, but
### Usage of `liburcu-signal`
- 1. `#include <urcu.h>`
- 2. Compile any `_LGPL_SOURCE` code using this library with `-DRCU_SIGNAL`
- 3. Link the application with `-lurcu-signal`
+ 1. `#include <urcu/urcu-signal.h>`
+ 2. Link the application with `-lurcu-signal`
Version of the library that requires a signal, typically `SIGUSR1`. Can
be overridden with `-DSIGRCU` by modifying `Makefile.build.inc`.
### Usage of `liburcu-bp`
- 1. `#include <urcu-bp.h>`
+ 1. `#include <urcu/urcu-bp.h>`
2. Link with `-lurcu-bp`
The BP library flavor stands for "bulletproof". It is specifically
designed to help tracing library to hook on applications without
-requiring to modify these applications. `rcu_init()`,
-`rcu_register_thread()` and `rcu_unregister_thread()` all become nops.
-The state is dealt with by the library internally at the expense of
-read-side and write-side performance.
+requiring to modify these applications. `urcu_bp_init()`, and
+`urcu_bp_unregister_thread()` all become nops, whereas calling
+`urcu_bp_register_thread()` becomes optional. The state is dealt with by
+the library internally at the expense of read-side and write-side
+performance.
### Initialization
Each thread that has reader critical sections (that uses
-`rcu_read_lock()`/`rcu_read_unlock()` must first register to the URCU
-library. This is done by calling `rcu_register_thread()`. Unregistration
-must be performed before exiting the thread by using
-`rcu_unregister_thread()`.
+`urcu_<flavor>_read_lock()`/`urcu_<flavor>_read_unlock()` must first
+register to the URCU library. This is done by calling
+`urcu_<flavor>_register_thread()`. Unregistration must be performed
+before exiting the thread by using `urcu_<flavor>_unregister_thread()`.
### Reading
Reader critical sections must be protected by locating them between
-calls to `rcu_read_lock()` and `rcu_read_unlock()`. Inside that lock,
-`rcu_dereference()` may be called to read an RCU protected pointer.
+calls to `urcu_<flavor>_read_lock()` and `urcu_<flavor>_read_unlock()`.
+Inside that lock, `rcu_dereference()` may be called to read an RCU
+protected pointer.
### Writing
`rcu_assign_pointer()` and `rcu_xchg_pointer()` may be called anywhere.
-After, `synchronize_rcu()` must be called. When it returns, the old
-values are not in usage anymore.
+After, `urcu_<flavor>_synchronize_rcu()` must be called. When it
+returns, the old values are not in usage anymore.
### Usage of `liburcu-defer`
- - Follow instructions for either `liburcu`, `liburcu-qsbr`,
+ - Follow instructions for either `liburcu-memb`, `liburcu-qsbr`,
`liburcu-mb`, `liburcu-signal`, or `liburcu-bp` above.
The `liburcu-defer` functionality is pulled into each of
those library modules.
- - Provides `defer_rcu()` primitive to enqueue delayed callbacks. Queued
- callbacks are executed in batch periodically after a grace period.
- Do _not_ use `defer_rcu()` within a read-side critical section, because
- it may call `synchronize_rcu()` if the thread queue is full.
- This can lead to deadlock or worse.
- - Requires that `rcu_defer_barrier()` must be called in library destructor
- if a library queues callbacks and is expected to be unloaded with
- `dlclose()`.
+ - Provides `urcu_<flavor>_defer_rcu()` primitive to enqueue delayed
+ callbacks. Queued callbacks are executed in batch periodically after
+ a grace period. Do _not_ use `urcu_<flavor>_defer_rcu()` within a
+ read-side critical section, because it may call
+ `urcu_<flavor>_synchronize_rcu()` if the thread queue is full. This
+ can lead to deadlock or worse.
+ - Requires that `urcu_<flavor>_defer_barrier()` must be called in
+ library destructor if a library queues callbacks and is expected to
+ be unloaded with `dlclose()`.
Its API is currently experimental. It may change in future library releases.
### Usage of `urcu-call-rcu`
- - Follow instructions for either `liburcu`, `liburcu-qsbr`,
+ - Follow instructions for either `liburcu-memb`, `liburcu-qsbr`,
`liburcu-mb`, `liburcu-signal`, or `liburcu-bp` above.
The `urcu-call-rcu` functionality is pulled into each of
those library modules.
- - Provides the `call_rcu()` primitive to enqueue delayed callbacks
- in a manner similar to `defer_rcu()`, but without ever delaying
- for a grace period. On the other hand, `call_rcu()`'s best-case
- overhead is not quite as good as that of `defer_rcu()`.
- - Provides `call_rcu()` to allow asynchronous handling of RCU
- 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 [`doc/rcu-api.md`](doc/rcu-api.md) in userspace-rcu documentation
- for more details.
+ - Provides the `urcu_<flavor>_call_rcu()` primitive to enqueue delayed
+ callbacks in a manner similar to `urcu_<flavor>_defer_rcu()`, but
+ without ever delaying for a grace period. On the other hand,
+ `urcu_<flavor>_call_rcu()`'s best-case overhead is not quite as good
+ as that of `urcu_<flavor>_defer_rcu()`.
+ - Provides `urcu_<flavor>_call_rcu()` to allow asynchronous handling
+ of RCU grace periods. A number of additional functions are provided
+ to manage the helper threads used by `urcu_<flavor>_call_rcu()`, but
+ reasonable defaults are used if these additional functions are not
+ invoked. See [`doc/rcu-api.md`](doc/rcu-api.md) in userspace-rcu
+ documentation for more details.
### Being careful with signals
-The `liburcu` library uses signals internally. The signal handler is
+The `liburcu-signal` library uses signals internally. The signal handler is
registered with the `SA_RESTART` flag. However, these signals may cause
some non-restartable system calls to fail with `errno = EINTR`. Care
should be taken to restart system calls manually if they fail with this
error. A list of non-restartable system calls may be found in
-`signal(7)`. The `liburcu-mb` and `liburcu-qsbr` versions of the Userspace RCU
-library do not require any signal.
+`signal(7)`.
Read-side critical sections are allowed in a signal handler,
-except those setup with `sigaltstack(2)`, with `liburcu` and
+except those setup with `sigaltstack(2)`, with `liburcu-memb` 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()`.
+between thread creation and calls to `urcu_<flavor>_register_thread()`,
+because a signal handler nesting on an unregistered thread would not be
+allowed to call `urcu_<flavor>_read_lock()`.
Read-side critical sections are _not_ allowed in a signal handler with
`liburcu-qsbr`, unless signals are disabled explicitly around each
-`rcu_quiescent_state()` calls, when threads are put offline and around
-calls to `synchronize_rcu()`. Even then, we do not recommend it.
+`urcu_qsbr_quiescent_state()` calls, when threads are put offline and around
+calls to `urcu_qsbr_synchronize_rcu()`. Even then, we do not recommend it.
### Interaction with mutexes
One must be careful to do not cause deadlocks due to interaction of
-`synchronize_rcu()` and RCU read-side with mutexes. If `synchronize_rcu()`
-is called with a mutex held, this mutex (or any mutex which has this
-mutex in its dependency chain) should not be acquired from within a RCU
-read-side critical section.
+`urcu_<flavor>_synchronize_rcu()` and RCU read-side with mutexes. If
+`urcu_<flavor>_synchronize_rcu()` is called with a mutex held, this
+mutex (or any mutex which has this 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()`).
+`urcu_qsbr_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 `urcu_qsbr_thread_offline()`).
### Interaction with `fork()`
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.
+`urcu_bp_before_fork`, `urcu_bp_after_fork_parent` and
+`urcu_bp_after_fork_child`.
+
+Applications that use `urcu_<flavor>_call_rcu()` and that `fork()`
+without doing an immediate `exec()` must take special action. The
+parent must invoke `urcu_<flavor>_call_rcu_before_fork()` before the
+`fork()` and `urcu_<flavor>_call_rcu_after_fork_parent()` after the
+`fork()`. The child process must invoke
+`urcu_<flavor>_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
+`urcu_<flavor>_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,
+ - call to `free()` from callbacks executed within
+ `urcu_<flavor>_call_rcu` worker threads,
+ - executing `urcu_<flavor>_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.
./configure --enable-rcu-debug
For fine grained enabling of debugging self-checks, build
-urserspace-rcu with DEBUG_RCU defined and compile dependent
+userspace-rcu with DEBUG_RCU defined and compile dependent
applications with DEBUG_RCU defined when necessary.
Warning: Enabling this feature result in a performance penalty.
theoretically yielding slightly better performance.
+### Usage of `--enable-cds-lfht-iter-debug`
+
+By default the library is configured with extra debugging checks for
+lock-free hash table iterator traversal disabled.
+
+Building liburcu with --enable-cds-lfht-iter-debug and rebuilding
+application to match the ABI change allows finding cases where the hash
+table iterator is re-purposed to be used on a different hash table while
+still being used to iterate on a hash table.
+
+This option alters the rculfhash ABI. Make sure to compile both library
+and application with matching configuration.
+
+
Make targets
------------
projects / urcu.git / blobdiff