Hi,
This is a release announcement for the Userspace RCU project.
This is a set of releases, including the new 0.14 branch with the 0.14.0
release, and bug fix releases for the 0.13 and 0.12 branches. The 0.12.5
release is the last of the 0.12 branch, which reaches end of life with
the release of 0.14.
Here are the new features introduced in urcu 0.14.0:
- C99 and C++11 are now the baseline requirements, as documented in
README.md.
- Introduce public APIs for C++,
An important point to consider: urcu/compiler.h needs to include
<type_traits> in C++, which prevents including urcu/compiler.h
from extern "C" code.
- Introduce new grace period polling APIs in urcu-memb,mb,signal,qsbr,bp
flavors:
struct urcu_gp_poll_state start_poll_synchronize_rcu(void);
bool poll_state_synchronize_rcu(struct urcu_gp_poll_state state);
This allow periodically polling to check if a started grace period has
completed, and thus check for grace period completion and some other
condition as well.
- rculfhash: introduce cds_lfht_node_init_deleted
Allow initializing lfht node to "removed" state to allow querying
whether the node is published in a hash table before it is added to
the hash table and after it has been removed from the hash table.
- Disable signals in URCU background threads
Applications using signalfd depend on signals being blocked in all
threads of the process, otherwise threads with unblocked signals
can receive them and starve the signalfd.
While some threads in URCU do block signals (e.g. workqueue
worker for rculfhash), the call_rcu, defer_rcu, and rculfhash
partition_resize_helper threads do not.
Always block all signals before creating threads, and only unblock
SIGRCU when registering a urcu-signal thread. Restore the SIGRCU
signal to its pre-registration blocked state on unregistration.
For rculfhash, cds_lfht_worker_init can be removed, because its only
effect is to block all signals except SIGRCU. Blocking all signals is
already done by the workqueue code, and unbloking SIGRCU is now done
by the urcu signal flavor thread regisration.
- Always use '__thread' for Thread local storage except on MSVC
Use the GCC extension '__thread' [1] for Thread local storage on all C
and C++ compilers except MSVC.
While C11 and C++11 respectively offer '_Thread_local' and
'thread_local' as potentialy faster implementations, they offer no
guarantees of compatibility when used in a library interface which
might be used by both C and C++ client code.
- Various test framework improvements.
- Wire up membarrier system call on Alpha. The only missing architecture
without membarrier wired up is MIPS. https://bugs.lttng.org/issues/940
Here are the fixes introduced in urcu 0.14.0, 0.13.3 and 0.12.5:
- Fix: auto-resize hash table destroy deadlock
Fix a deadlock for auto-resize hash tables when cds_lfht_destroy
is called with RCU read-side lock held.
- Join call_rcu worker thread in call_rcu_data_free (eliminate leaks)
- Teardown default call_rcu worker on application exit
Teardown the default call_rcu worker thread if there are no queued
callbacks on process exit. This prevents leaking memory.
Here is how an application can ensure graceful teardown of this
worker thread:
- An application queuing call_rcu callbacks should invoke
rcu_barrier() before it exits.
- When chaining call_rcu callbacks, the number of calls to
rcu_barrier() on application exit must match at least the maximum
number of chained callbacks.
- If an application chains callbacks endlessly, it would have to be
modified to stop chaining callbacks when it detects an application
exit (e.g. with a flag), and wait for quiescence with rcu_barrier()
after setting that flag.
- The statements above apply to a library which queues call_rcu
callbacks, only it needs to invoke rcu_barrier in its library
destructor.
- Allow building on MSYS2
Update cygwin libtool config in `configure.ac` to match MSYS2 build
environments as well. MSYS2 is also a Windows build environment that
produces DLLs.
Feedback is welcome!
Mathieu
Project website: https://liburcu.org
Git repository: git://git.liburcu.org/urcu.git
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com