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## History

#### Version 4.5.0 - boost 1.58

Know Bugs:

- #3926 thread_specific_ptr + dlopen library causes a SIGSEGV.
- #4833 MinGW/test_tss_lib: Support of automatic tss cleanup for native threading API not available
- #8600 wait_for_any hangs, if called with multiple copies of shared_future referencing same task
- #9118 Seg fault on thread join when llvm and libc++ are used
- #9309 test_latch fails often on clang-darwin-tot11
- #9311 ex_lambda_future fails on msvc-11.0
- #10942 Boost.Thread fails to build on Cygwin.

Please take a look at thread Know Bugs to see the current state.

Please take a look at thread trunk regression test to see the last regression test snapshot.

Sever limitations:

There are some severe bugs that prevent the use of the library on concrete contexts, in particular:

- on thread specific storage that prevent the library to be used with dynamic libraries ( #3926, ),

New Experimental Features:

- #9600 Async: Add task_region
- #10611 Add emplace promise::set_value and emplace make_ready_future
- #10826 Add scheduled executor operations
- #11048 Add a serial_executor based on continuations

Fixed Bugs:

- #6787 boost::thread::sleep() hangs if system time is rolled back
- #10734 Submit method work differently on different executors, some throw exception and some silently ignore error (thread_executor and inline_executor)
- #10736 Task exceptions silently ignored. I think std::terminate solution from N3785 and std::thread is better choice and more consistent.
- #10737 In serial_executor we have infinite wait if task throw exception.
- #10822 Boost.Thread fails to compile on Android
- #10824 Boost.Thread 1.57 breaks Windows XP compatibility for SP2 and below.
- #10963 future<future<T>>::then Has No Implementation
- #10964 future<future<T>>::unwrap().then() Deadlocks
- #10968 The futures returned by async() and future::then() are not blocking.
- #10971 shared_future::get()/get_or() must be const
- #10972 shared_future::then() can be called multiple times.
- #10979 Support T& type deduction when the make_ready_future parameter is reference_wrapper<T>
- #10996 Thread physical_concurrency() is failing on Windows
- #11035 BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE not defined for Android
- #11053 The attached code results in a R6025 - pure virtual function call in run_thread_exit_callbacks

#### Version 4.4.0 - boost 1.57

Know Bugs:

- #2442 Application statically linked with Boost.Thread crashes when Google Desktop is installed (Windows XP)
- #3926 thread_specific_ptr + dlopen library causes a SIGSEGV.
- #4833 MinGW/test_tss_lib: Support of automatic tss cleanup for native threading API not available
- #7319 Take care of c++std-lib-32966 issue
- #8600 wait_for_any hangs, if called with multiple copies of shared_future referencing same task
- #9118 Seg fault on thread join when llvm and libc++ are used
- #9309 test_latch fails often on clang-darwin-tot11
- #9310 test_4648_lib fails on clang-darwin-asan11
- #9311 ex_lambda_future fails on msvc-11.0
- #10537 Application crash on throw exception
- #10651 boost::thread leaks memory when using the MinGW compiler

Please take a look at thread Know Bugs to see the current state.

Please take a look at thread trunk regression test to see the last snapshot.

Sever limitations:

There are some severe bugs that prevent the use of the library on concrete contexts, in particular:

- on thread specific storage that prevent the library to be used with dynamic libraries,

New Experimental Features:

- #6227 Synchro: Use of variadic templates on Generic Locking Algorithms on compilers providing them
- #10298 Synchro: Added queue views.
- #10300 Async: Added generic_executor_ref.
- #10552 Add make_valid_future

Fixed Bugs:

- #6782 call_once uses incorrect barrier intrinsic on Visual Studio
- #6787 boost::thread::sleep() hangs if system time is rolled back
- #7665 this_thread::sleep_for no longer uses steady_clock in thread
- #9307 future::fallback_to assert with ERRORRRRR boost: mutex lock failed in pthread_mutex_lock: Invalid argument
- #9308 future::async fails with terminate called throwing an exception when called with a lambda - clang-darwin-asan11
- #9310 test_4648_lib fails on clang-darwin-asan11
- #9425 Boost promise & future does not use supplied allocator for value storage
- #9558 future continuations unit test hangs in get()/pthread_cond_wait() on Mac 10.7/32-bit/x86/darwin-4.2.1
- #9787 [windows] Small duration value passed down to basic_timed_mutex::try_lock_until and condition_variable::wait_until can cause infinite or near infinite wait for win32
- #9880 [windows] boost::condition_variable.timed_wait() exception if system time < 1970
- #10159 GCC 4.4 error sorry, unimplemented
- #10196 thread_specific_ptr does not support void*
- #10296 Boost.Thread 1.56 rc1 does not compile on Mingw
- #10297 Boost.Thread 1.56 rc1 hangs when built with clang on armhf
- #10340 No boost::promise<T>::set_value(const T&) overload present in C++03 mode
- #10425 Missing documentation for when_all/when_any.
- #10426 Take in account the deferred futures in when_all.
- #10427 Take in account the deferred and ready futures in when_any.
- #10428 Adapt to new unique_ptr interface in Boost.Move
- #10465 Missing implementation of when_all/when_any when the result is a tuple.
- #10476 classes using BOOST_THREAD_MOVABLE_ONLY<T> dont satisfy is_copy_constructible<T>::value == false
- #10478 Data race in boost/thread/future.hpp
- #10529 The pthread/condition_variable_any constructor reports incorrect error code for pthread_cond_init
- #10563 shared_future<R>::then should be const

#### Version 4.3.0 - boost 1.56

Know Bugs:

- #2442 Application statically linked with Boost.Thread crashes when Google Desktop is installed (Windows XP)
- #3926 thread_specific_ptr + dlopen library causes a SIGSEGV.
- #4833 MinGW/test_tss_lib: Support of automatic tss cleanup for native threading API not available
- #6782 call_once uses incorrect barrier intrinsic on Visual Studio
- #7319 Take care of c++std-lib-32966 issue
- #8600 wait_for_any hangs, if called with multiple copies of shared_future referencing same task
- #9307 future::fallback_to assert with ERRORRRRR boost: mutex lock failed in pthread_mutex_lock: Invalid argument
- #9308 future::async fails with terminate called throwing an exception when called with a lambda - clang-darwin-asan11
- #9310 test_4648_lib fails on clang-darwin-asan11
- #9311 ex_lambda_future fails on msvc-11.0
- #9425 Boost promise & future does not use supplied allocator for value storage
- #9558 future continuations unit test hangs in get()/pthread_cond_wait() on Mac 10.7/32-bit/x86/darwin-4.2.1

Please take a look at thread Know Bugs to see the current state.

Please take a look at thread trunk regression test to see the last snapshot.

Sever limitations:

There are some severe bugs that prevent the use of the library on concrete contexts, in particular:

- on thread specific storage that prevent the library to be used with dynamic libraries,
- The experimental features of boost::future have some severe holes that make the program crash unexpectedly.

New Experimental Features:

- #7446 Async: Add when_any.
- #7447 Async: Add when_all.
- #7448 Async: Add async taking a scheduler parameter.
- #8274 Synchro: Add concurrent queue
- #8518 Synchro: Add a latch class.
- #8513 Async: Add a basic thread_pool executor.
- #8516 Async: Add future/shared_future::then taking a scheduler as parameter.

Fixed Bugs:

- #8070 prefer GetTickCount64 over GetTickCount
- #9333 ex_scoped_thread compile fails on msvc-12.0
- #9366 async(Executor, ...) fails to compile with msvc-10,11,12
- #9402 test_excutor regression on msvc-10,11,12
- #9404 ex_make_future regression error
- #9471 Synchronization documentation nits
- #9535 Missing exception safety might result in crash
- #9618 try_join_for problem: program is not terminate.
- #9673 thread compilation with MingW/gcc on Windows gives errors
- #9708 boost::condition_variable::timed_wait unexpectedly wakes up while should wait infinite
- #9711 future continuation called twice

#### Version 4.2.0 - boost 1.55

Know Bugs:

- #2442 Application statically linked with Boost.Thread crashes when Google Desktop is installed (Windows XP)
- #3926 thread_specific_ptr + dlopen library causes a SIGSEGV.
- #4833 MinGW/test_tss_lib: Support of automatic tss cleanup for native threading API not available
- #6782 call_once uses incorrect barrier intrinsic on Visual Studio
- #7319 Take care of c++std-lib-32966 issue
- #8600 wait_for_any hangs, if called with multiple copies of shared_future referencing same task
- #9307 future::fallback_to assert with ERRORRRRR boost: mutex lock failed in pthread_mutex_lock: Invalid argument
- #9308 future::async fails with terminate called throwing an exception when called with a lambda - clang-darwin-asan11
- #9311 ex_lambda_future fails on msvc-11.0
- #9310 test_4648_lib fails on clang-darwin-asan11

Please take a look at thread trunk regression test to see the current state.

Sever limitations:

There are some severe bugs that prevent the use of the library on concrete contexts, in particular:

- on thread specific storage that prevent the library to be used with dynamic libraries,
- The experimental features of boost::future have some severe holes that make the program crash unexpectedly.

New Features:

- #8519 Synchro: Update class barrier with a completion function.
- #8515 Async: Add shared_future::then.
- #8519 Synchro: Update class barrier with a completion function
- #8615 Async: Replace make_future/make_shared_future by make_ready_future.
- #8627 Async: Add future<>::unwrap and unwrapping constructor.
- #8677 Async: Add future<>::get_or.
- #8678 Async: Add future<>::fallback_to.
- #8891 upgrade_to_unique_lock: missing mutex() function.
- #8955 Request for more efficient way to get exception_ptr from future.

Fixed Bugs:

- #7461 detail::win32::ReleaseSemaphore may be called with count_to_release equal to 0
- #8070 prefer GetTickCount64 over GetTickCount
- #8768 win32 condition_variable::wait_until infinite wait in rare cases.
- #8817 Boost Thread Windows CE _createthreadex handling breaks mingw w64.
- #8943 Failed to compile code using boost::call_once with Intel C++ Composer XE 2013 on Windows.
- #8931 Typos in external_locking reference.
- #9029 Misprint in documentation.
- #9037 gcc -Wshadow gives warnings in condition_variable{,_fwd}.hpp.
- #9041 Boost.Thread DSO's may need to link with Boost.Atomic.
- #9048 boost::scoped_thread useless ctor with variadic template arguments.
- #9079 Condition variable will wait forever for some timepoint values (Win).

#### Version 4.1.0 - boost 1.54

New Features:

- #7285 C++11 compliance: Allow to pass movable arguments for call_once.
- #7445 Async: Add future<>.then
- #7449 Synchro: Add a synchronized value class

Fixed Bugs:

- #4878 MinGW 4.5.0 undefined reference to bool interruptible_wait(detail::win32::handle handle_to_wait_for,detail::t imeout target_time).
- #4882 Win32 shared_mutex does not handle timeouts correctly.
- #5752 boost::call_once() is unreliable on some platforms
- #6652 Boost.Thread shared_mutex.hpp:50:99: warning: dereferencing type-punned pointer will break strict-aliasing rules Wstrict-aliasing
- #6843 [Intel C++] Compile Errors with '#include <atomic>'
- #6966 future boost::future_category inconsistent dll linkage
- #7720 exception lock_error while intensive locking/unlocking of mutex
- #7755 Thread: deadlock with shared_mutex on Windows
- #7980 Build error: msvc-11.0 and BOOST_THREAD_DONT_USE_DATETIME
- #7982 pthread_delay_np() parm compile error on AIX
- #8027 thread library fails to compile with Visual Studio 2003
- #8070 prefer GetTickCount64 over GetTickCount
- #8136 boost::this_thread::sleep_for() sleeps longer than it should in Windows
- #8212 Boost thread compilation error on Solaris 10
- #8237 fix documentation for 'thread_group'
- #8239 barrier::wait() not marked as interruption_point
- #8323 boost::thread::try_join_for/try_join_until may block indefinitely due to a combination of problems in Boost.Thread and Boost.Chrono
- #8337 The internal representation of "std::string(this->code()->message())" escapes, but is destroyed when it exits scope.
- #8371 C++11 once_flag enabled when constexpr is not available
- #8422 Assertion in win32::WaitForSingleObject()
- #8443 Header file inclusion order may cause crashes
- #8451 Missing documented function 'boost::scoped_thread::joinable'
- #8458 -DBOOST_THREAD_DONT_USE_CHRONO in thread.obj.rsp but not explicitly set
- #8530 [Coverity] Unused variable thread_handle, uninitialized variable cond_mutex in thread/pthread/thread_data.hpp
- #8550 static linking of Boost.Thread with an MFC-Dll
- #8576 "sur parolle" should be "sur parole".
- #8596 With C++0x enabled, boost::packaged_task stores a reference to function objects, instead of a copy.
- #8626 Reintroduce BOOST_VERIFY on pthread_mutex_destroy return type
- #8645 Typo in Strict lock definition
- #8671 promise: set_..._at_thread_exit
- #8672 future<>::then(void()) doesn't works
- #8674 Futures as local named objects can't be returned with implicit move.

#### Version 4.0.0 - boost 1.53

Deprecated features:

| Warning
Deprecated features since boost 1.53 will be available only until boost 1.58.

- C++11 compliance: packaged_task<R> is deprecated, use instead packaged_task<R()>. See BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK and BOOST_THREAD_DONT_PROVIDE_SIGNATURE_PACKAGED_TASK
- #7537 deprecate Mutex::scoped_lock and scoped_try_lock and boost::condition

New Features:

- #6270 c++11 compliance: Add thread constructor from movable callable and movable arguments Provided when BOOST_THREAD_PROVIDES_VARIADIC_THREAD is defined (Default value from Boost 1.55): See BOOST_THREAD_PROVIDES_VARIADIC_THREAD and BOOST_THREAD_DONT_PROVIDE_VARIADIC_THREAD.
- #7279 C++11 compliance: Add noexcept in system related functions
- #7280 C++11 compliance: Add promise::...at_thread_exit functions
- #7281 C++11 compliance: Add ArgTypes to packaged_task template. Provided when BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK is defined (Default value from Boost 1.55). See BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK and BOOST_THREAD_DONT_PROVIDE_SIGNATURE_PACKAGED_TASK.
- #7282 C++11 compliance: Add packaged_task::make_ready_at_thread_exit function
- #7285 C++11 compliance: Allow to pass movable arguments for call_once
- #7412 C++11 compliance: Add async from movable callable and movable arguments Provided when BOOST_THREAD_PROVIDES_VARIADIC_THREAD and BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK are defined (Default value from Boost 1.55): See BOOST_THREAD_PROVIDES_SIGNATURE_PACKAGED_TASK and BOOST_THREAD_DONT_PROVIDE_SIGNATURE_PACKAGED_TASK, BOOST_THREAD_PROVIDES_VARIADIC_THREAD and BOOST_THREAD_DONT_PROVIDE_VARIADIC_THREAD.
- #7413 C++11 compliance: Add async when the launch policy is deferred.
- #7414 C++11 compliance: future::get post-condition should be valid()==false.
- #7422 Provide a condition variable with zero-overhead performance penality.
- #7444 Async: Add make_future/make_shared_future.
- #7540 Threads: Add a helper class that join a thread on destruction.
- #7541 Threads: Add a thread wrapper class that joins on destruction.
- #7575 C++11 compliance: A future created by async should "join" in the destructor.
- #7587 Synchro: Add strict_lock and nested_strict_lock.
- #7588 Synchro: Split the locks.hpp in several files to limit dependencies.
- #7590 Synchro: Add lockable concept checkers based on Boost.ConceptCheck.
- #7591 Add lockable traits that can be used with enable_if.
- #7592 Synchro: Add a null_mutex that is a no-op and that is a model of UpgardeLockable.
- #7593 Synchro: Add a externally_locked class.
- #7594 Threads: Allow to disable thread interruptions.

Fixed Bugs:

- #5752 boost::call_once() is unreliable on some platforms
- #7464 BOOST_TEST(n_alive == 1); fails due to race condition in a regression test tool.
- #7657 Serious performance and memory consumption hit if condition_variable methods condition notify_one or notify_all is used repeatedly.
- #7665 this_thread::sleep_for no longer uses steady_clock in thread.
- #7668 thread_group::join_all() should check whether its threads are joinable.
- #7669 thread_group::join_all() should catch resource_deadlock_would_occur.
- #7671 Error including boost/thread.hpp header on iOS.
- #7672 lockable_traits.hpp syntax error: "defined" token misspelled.
- #7798 boost::future set_wait_callback thread safety issues.
- #7808 Incorrect description of effects for this_thread::sleep_for and this_thread::sleep_until.
- #7812 Returns: cv_status::no_timeout if the call is returning because the time period specified by rel_time has elapsed, cv_status::timeout otherwise.
- #7874 compile warning: thread.hpp:342: warning: type attributes are honored only at type definition.
- #7875 BOOST_THREAD_THROW_IF_PRECONDITION_NOT_SATISFIED should not be enabled by default.
- #7882 wrong exception text from condition_variable::wait(unique_lock<mutex>&).
- #7890 thread::do_try_join_until() is missing a return type.

#### Version 3.1.0 - boost 1.52

Deprecated Features:

Deprecated features since boost 1.50 available only until boost 1.55:

These deprecated features will be provided by default up to boost 1.52. If you don't want to include the deprecated features you could define BOOST_THREAD_DONT_PROVIDE_DEPRECATED_FEATURES_SINCE_V3_0_0. Since 1.53 these features will not be included any more by default. Since this version, if you want to include the deprecated features yet you could define BOOST_THREAD_PROVIDE_DEPRECATED_FEATURES_SINCE_V3_0_0. These deprecated features will be only available until boost 1.55, that is you have yet 1 year to move to the new features.

- Time related functions don't using the Boost.Chrono library, use the chrono overloads instead.

Breaking changes when BOOST_THREAD_VERSION==3 (Default value since Boost 1.53):

There are some new features which share the same interface but with different behavior. These breaking features are provided by default when BOOST_THREAD_VERSION is 3, but the user can however choose the version 2 behavior by defining the corresponding macro. As for the deprecated features, these broken features will be only available until boost 1.55.

- #6229 Rename the unique_future to future following the c++11.
- #6266 Breaking change: thread destructor should call terminate if joinable.
- #6269 Breaking change: thread move assignment should call terminate if joinable.

New Features:

- #2361 thread_specific_ptr: document nature of the key, complexity and rationale.
- #4710 C++11 compliance: Missing async().
- #7283 C++11 compliance: Add notify_all_at_thread_exit.
- #7345 C++11 compliance: Add noexcept to recursive mutex try_lock.

Fixed Bugs:

- #2797 Two problems with thread_specific_ptr.
- #5274 failed to compile future.hpp with stlport 5.1.5 under msvc8.1, because of undefined class.
- #5431 compile error in Windows CE 6.0(interlocked).
- #5696 win32 detail::set_tss_data does nothing when tss_cleanup_function is NULL.
- #6931 mutex waits forwever with Intel C++ Compiler XE 12.1.5.344 Build 20120612
- #7045 Thread library does not automatically compile date_time.
- #7173 wrong function name interrupt_point().
- #7200 Unable to build boost.thread modularized.
- #7220 gcc 4.6.2 warns about inline+dllimport functions.
- #7238 this_thread::sleep_for() does not respond to interrupt().
- #7245 Minor typos on documentation related to version 3.
- #7272 win32/thread_primitives.hpp: (Unneccessary) Warning.
- #7284 Clarify that there is no access priority between lock and shared_lock on shared mutex.
- #7329 boost/thread/future.hpp does not compile on HPUX.
- #7336 BOOST_THREAD_DONT_USE_SYSTEM doesn't work.
- #7349 packaged_task holds reference to temporary.
- #7350 allocator_destructor does not destroy object
- #7360 Memory leak in pthread implementation of boost::thread_specific_ptr
- #7370 Boost.Thread documentation
- #7438 Segmentation fault in test_once regression test in group.join_all();
- #7461 detail::win32::ReleaseSemaphore may be called with count_to_release equal to 0
- #7499 call_once doesn't call even once

#### Version 3.0.1 - boost 1.51

Deprecated Features:

Deprecated features since boost 1.50 available only until boost 1.55:

These deprecated features will be provided by default up to boost 1.52. If you don't want to include the deprecated features you could define BOOST_THREAD_DONT_PROVIDE_DEPRECATED_FEATURES_SINCE_V3_0_0. Since 1.53 these features will not be included any more by default. Since this version, if you want to include the deprecated features yet you could define BOOST_THREAD_PROVIDE_DEPRECATED_FEATURES_SINCE_V3_0_0. These deprecated features will be only available until boost 1.55, that is you have 1 year and a half to move to the new features.

- Time related functions don't using the Boost.Chrono library, use the chrono overloads instead.

Breaking changes when BOOST_THREAD_VERSION==3:

There are some new features which share the same interface but with different behavior. These breaking features are provided by default when BOOST_THREAD_VERSION is 3, but the user can however choose the version 2 behavior by defining the corresponding macro. As for the deprecated features, these broken features will be only available until boost 1.55.

- #6229 Rename the unique_future to future following the c++11.
- #6266 Breaking change: thread destructor should call terminate if joinable.
- #6269 Breaking change: thread move assignment should call terminate if joinable.

Fixed Bugs:

- #4258 Linking with boost thread does not work on mingw/gcc 4.5.
- #4885 Access violation in set_tss_data at process exit due to invalid assumption about TlsAlloc.
- #6931 mutex waits forwever with Intel Compiler and /debug:parallel
- #7044 boost 1.50.0 header missing.
- #7052 Thread: BOOST_THREAD_PROVIDES_DEPRECATED_FEATURES_SINCE_V3_0_0 only masks thread::operator==, thread::operator!= forward declarations, not definitions.
- #7066 An attempt to fix current_thread_tls_key static initialization order.
- #7074 Multiply defined symbol boost::allocator_arg.
- #7078 Trivial 64-bit warning fix on Windows for thread attribute stack size
- #7089 BOOST_THREAD_WAIT_BUG limits functionality without solving anything

#### Version 3.0.0 - boost 1.50

Breaking changes when BOOST_THREAD_VERSION==3:

- #6229 Breaking change: Rename the unique_future to future following the c++11.
- #6266 Breaking change: thread destructor should call terminate if joinable.
- #6269 Breaking change: thread move assignment should call terminate if joinable.

New Features:

- #1850 Request for unlock_guard to compliment lock_guard.
- #2637 Request for shared_mutex duration timed_lock and timed_lock_shared.
- #2741 Proposal to manage portable and non portable thread attributes.
- #3567 Request for shared_lock_guard.
- #6194 Adapt to Boost.Move.
- #6195 c++11 compliance: Provide the standard time related interface using Boost.Chrono.
- #6217 Enhance Boost.Thread shared mutex interface following Howard Hinnant proposal.
- #6224 c++11 compliance: Add the use of standard noexcept on compilers supporting them.
- #6225 Add the use of standard =delete defaulted operations on compilers supporting them.
- #6226 c++11 compliance: Add explicit bool conversion from locks.
- #6228 Add promise constructor with allocator following the standard c++11.
- #6230 c++11 compliance: Follows the exception reporting mechanism as defined in the c++11.
- #6231 Add BasicLockable requirements in the documentation to follow c++11.
- #6272 c++11 compliance: Add thread::id hash specialization.
- #6273 c++11 compliance: Add cv_status enum class and use it on the conditions wait functions.
- #6342 c++11 compliance: Adapt the one_flag to the c++11 interface.
- #6671 upgrade_lock: missing mutex and release functions.
- #6672 upgrade_lock:: missing constructors from time related types.
- #6675 upgrade_lock:: missing non-member swap.
- #6676 lock conversion should be explicit.
- Added missing packaged_task::result_type and packaged_task:: constructor with allocator.
- Added packaged_task::reset()

Fixed Bugs:

- #2380 boost::move from lvalue does not work with gcc.
- #2430 shared_mutex for win32 doesn't have timed_lock_upgrade.
- #2575 Bug- Boost 1.36.0 on Itanium platform.
- #3160 Duplicate tutorial code in boost::thread.
- #4345 thread::id and joining problem with cascade of threads.
- #4521 Error using boost::move on packaged_task (MSVC 10).
- #4711 Must use implementation details to return move-only types.
- #4921 BOOST_THREAD_USE_DLL and BOOST_THREAD_USE_LIB are crucial and need to be documented.
- #5013 documentation: boost::thread: pthreas_exit causes terminate().
- #5173 boost::this_thread::get_id is very slow.
- #5351 interrupt a future get boost::unknown_exception.
- #5516 Upgrade lock is not acquired when previous upgrade lock releases if another read lock is present.
- #5990 shared_future<T>::get() has wrong return type.
- #6174 packaged_task doesn't correctly handle moving results.
- #6222 Compile error with SunStudio: unique_future move.
- #6354 PGI: Compiler threading support is not turned on.
- #6673 shared_lock: move assign doesn't works with c++11.
- #6674 shared_mutex: try_lock_upgrade_until doesn't works.
- #6908 Compile error due to unprotected definitions of _WIN32_WINNT and WINVER.
- #6940 TIME_UTC is a macro in C11.
- #6959 call of abs is ambiguous.
- Fix issue signaled on the ML with task_object(task_object const&) in presence of task_object(task_object &&)

#### Version 2.1.1 - boost 1.49

Fixed Bugs:

- #2309 Lack of g++ symbol visibility support in Boost.Thread.
- #2639 documentation should be extended(defer_lock, try_to_lock, ...).
- #3639 Boost.Thread doesn't build with Sun-5.9 on Linux.
- #3762 Thread can't be compiled with winscw (Codewarrior by Nokia).
- #3885 document about mix usage of boost.thread and native thread api.
- #3975 Incorrect precondition for promise::set_wait_callback().
- #4048 thread::id formatting involves locale
- #4315 gcc 4.4 Warning: inline ... declared as dllimport: attribute ignored.
- #4480 OpenVMS patches for compiler issues workarounds.
- #4819 boost.thread's documentation misprints.
- #5423 thread issues with C++0x.
- #5617 boost::thread::id copy ctor.
- #5739 set-but-not-used warnings with gcc-4.6.
- #5826 threads.cpp: resource leak on threads creation failure.
- #5839 thread.cpp: ThreadProxy leaks on exceptions.
- #5859 win32 shared_mutex constructor leaks on exceptions.
- #6100 Compute hardware_concurrency() using get_nprocs() on GLIBC systems.
- #6168 recursive_mutex is using wrong config symbol (possible typo).
- #6175 Compile error with SunStudio.
- #6200 patch to have condition_variable and mutex error better handle EINTR.
- #6207 shared_lock swap compiler error on clang 3.0 c++11.
- #6208 try_lock_wrapper swap compiler error on clang 3.0 c++11.

#### Version 2.1.0 - Changes since boost 1.40

The 1.41.0 release of Boost adds futures to the thread library. There are also a few minor changes.

#### Changes since boost 1.35

The 1.36.0 release of Boost includes a few new features in the thread library:

- New generic `lock()` and `try_lock()` functions for locking multiple mutexes at once.
- Rvalue reference support for move semantics where the compilers supports it.
- A few bugs fixed and missing functions added (including the serious win32 condition variable bug).
- `scoped_try_lock` types are now backwards-compatible with Boost 1.34.0 and previous releases.
- Support for passing function arguments to the thread function by supplying additional arguments to the `boost::thread` constructor.
- Backwards-compatibility overloads added for `timed_lock` and `timed_wait` functions to allow use of `xtime` for timeouts.

#### Version 2.0.0 - Changes since boost 1.34

Almost every line of code in Boost.Thread has been changed since the 1.34 release of boost. However, most of the interface changes have been extensions, so the new code is largely backwards-compatible with the old code. The new features and breaking changes are described below.

#### New Features

- Instances of `boost::thread` and of the various lock types are now movable.
- Threads can be interrupted at interruption points.
- Condition variables can now be used with any type that implements the `Lockable` concept, through the use of `boost::condition_variable_any` (`boost::condition` is a `typedef` to `boost::condition_variable_any`, provided for backwards compatibility). `boost::condition_variable` is provided as an optimization, and will only work with `boost::unique_lock<boost::mutex>` (`boost::mutex::scoped_lock`).
- Thread IDs are separated from `boost::thread`, so a thread can obtain it's own ID (using `boost::this_thread::get_id()`), and IDs can be used as keys in associative containers, as they have the full set of comparison operators.
- Timeouts are now implemented using the Boost DateTime library, through a typedef `boost::system_time` for absolute timeouts, and with support for relative timeouts in many cases. `boost::xtime` is supported for backwards compatibility only.
- Locks are implemented as publicly accessible templates `boost::lock_guard`, `boost::unique_lock`, `boost::shared_lock`, and `boost::upgrade_lock`, which are templated on the type of the mutex. The `Lockable` concept has been extended to include publicly available `lock()` and `unlock()` member functions, which are used by the lock types.

#### Breaking Changes

The list below should cover all changes to the public interface which break backwards compatibility.

- `boost::try_mutex` has been removed, and the functionality subsumed into `boost::mutex`. `boost::try_mutex` is left as a `typedef`, but is no longer a separate class.
- `boost::recursive_try_mutex` has been removed, and the functionality subsumed into `boost::recursive_mutex`. `boost::recursive_try_mutex` is left as a `typedef`, but is no longer a separate class.
- `boost::detail::thread::lock_ops` has been removed. Code that relies on the `lock_ops` implementation detail will no longer work, as this has been removed, as it is no longer necessary now that mutex types now have public `lock()` and `unlock()` member functions.
- `scoped_lock` constructors with a second parameter of type `bool` are no longer provided. With previous boost releases,

      boost::mutex::scoped_lock some_lock(some_mutex,false);

  could be used to create a lock object that was associated with a mutex, but did not lock it on construction. This facility has now been replaced with the constructor that takes a `boost::defer_lock_type` as the second parameter:

      boost::mutex::scoped_lock some_lock(some_mutex,boost::defer_lock);

- The `locked()` member function of the `scoped_lock` types has been renamed to `owns_lock()`.
- You can no longer obtain a `boost::thread` instance representing the current thread: a default-constructed `boost::thread` object is not associated with any thread. The only use for such a thread object was to support the comparison operators: this functionality has been moved to `boost::thread::id`.
- The broken `boost::read_write_mutex` has been replaced with `boost::shared_mutex`.
- `boost::mutex` is now never recursive. For Boost releases prior to 1.35 `boost::mutex` was recursive on Windows and not on POSIX platforms.
- When using a `boost::recursive_mutex` with a call to `boost::condition_variable_any::wait()`, the mutex is only unlocked one level, and not completely. This prior behaviour was not guaranteed and did not feature in the tests.