[RELEASE] Userspace RCU 0.14.0, 0.13.3, 0.12.5 [EOL]

[Mathieu Desnoyers]

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