When converting from a coarse duration with a very large value, the
existing code scales that up to chrono::seconds which overflows the
chrono::seconds::rep type. For example, sleep_for(chrono::hours::max())
tries to calculate LLONG_MAX * 3600, which overflows to -3600 and so the
sleep returns immediately.
The solution in this commit is inspired by this_thread::sleep_for in
libc++ which compares the duration argument to
chrono::duration<long double>(nanoseconds::max()) and limits the
duration to nanoseconds::max(). Because we split the duration into
seconds and nanoseconds, we can use seconds::max() as our upper limit.
We might need to limit further if seconds::max() doesn't fit in the
type used for sleeping, which is one of std::time_t, unsigned int, or
chrono::milliseconds.
To fix this everywhere that uses timeouts, new functions are introduced
for converting from a chrono::duration or chrono::time_point to a
timespec (or __gthread_time_t which is just a timespec on Linux). These
functions provide one central place where we can avoid overflow and also
handle negative timeouts (as these produce errors when passed to OS
functions that do not accept absolute times before the epoch). All
negative durations are converted to zero, and negative time_points are
converted to the epoch.
The new __to_timeout_gthread_time_t function in <bits/std_mutex.h>
requires adding <bits/chrono.h> to that header, but that only affects
<syncstream>. All other consumers of <bits/std_mutex.h> were already
including <bits/chrono.h> for timeouts (e.g. <shared_mutex> and
<condition_variable>).
libstdc++-v3/ChangeLog:
PR libstdc++/113327
PR libstdc++/116586
PR libstdc++/119258
PR libstdc++/58931
* include/bits/chrono.h (__to_timeout_timespec): New overloaded
function templates for converting chrono types to timespec.
* include/bits/std_mutex.h (__to_timeout_gthread_time_t): New
function template for converting time_point to __gthread_time_t.
* include/bits/this_thread_sleep.h (sleep_for): Use
__to_timeout_timespec.
(__sleep_for): Remove namespace-scope declaration.
* include/std/condition_variable: Likewise.
* include/std/mutex: Likewise.
* include/std/shared_mutex: Likewise.
* src/c++11/thread.cc (limit): New helper function.
(__sleep_for): Use limit to prevent overflow when converting
chrono::seconds to time_t, unsigned, or chrono::milliseconds.
* src/c++20/atomic.cc: Use __to_timeout_timespec and
__to_timeout_gthread_time_t for timeouts.
* testsuite/30_threads/this_thread/113327.cc: New test.
Reviewed-by: Mike Crowe <mac@mcrowe.com>
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Adding this attribute means users get a warning when they accidentally
create a temporary lock instead of creating an automatic variable with
block scope.
For std::lock_guard both constructors have side effects (they both take
a mutex and so both cause it to be unlocked at the end of the full
expression when a temporary is constructed). Ideally we would just put
the attribute on the class instead of the constructors, but that doesn't
work with GCC (PR c++/85973).
For std::unique_lock the default constructor and std::defer_lock_t
constructor do not cause any locking or unlocking, so do not need to
give a warning. It might still be a mistake to create a temporary using
those constructors, but it's harmless and seems unlikely anyway. For a
lock object created with one of those constructors you would expect the
lock object to be referred to later in the function, and that would not
even compile if it was constructed as an unnamed temporary.
std::scoped_lock gets the same treatment as std::lock_guard, except that
the explicit specialization for zero lockables has no side effects so
doesn't need to warn.
libstdc++-v3/ChangeLog:
* include/bits/std_mutex.h (lock_guard): Add [[nodiscard]]
attribute to constructors.
* include/bits/unique_lock.h (unique_lock): Likewise.
* include/std/mutex (scoped_lock, scoped_lock<Mutex>): Likewise.
* testsuite/30_threads/lock_guard/cons/nodiscard.cc: New test.
* testsuite/30_threads/scoped_lock/cons/nodiscard.cc: New test.
* testsuite/30_threads/unique_lock/cons/nodiscard.cc: New test.
This needs to be included explicitly now that we don't include all of
<system_error> here.
libstdc++-v3/ChangeLog:
* include/bits/std_mutex.h: Include <errno.h>.
The <condition_variable>, <mutex>, and <shared_mutex> headers use
std::errc constants, but don't use std::system_error itself. They only
use the __throw_system_error(int) function, which is defined in
<bits/functexcept.h>.
By including the header for the errc constants instead of the whole of
<system_error> we avoid depending on the whole std::string definition.
libstdc++-v3/ChangeLog:
* include/bits/std_mutex.h: Remove <system_error> include.
* include/std/condition_variable: Add <bits/error_constants.h>
include.
* include/std/mutex: Likewise.
* include/std/shared_mutex: Likewise.
std::condition_variable::wait(unique_lock<mutex>&) is incorrectly marked
noexcept, which means that the __forced_unwind exception used by NPTL
cancellation will terminate the process. It should allow exceptions to
pass through, so that a thread can be cleanly cancelled when waiting on
a condition variable.
The new behaviour is exported as a new version of the symbol, to avoid
an ABI break for existing code linked to the non-throwing definition of
the function. Code linked against older releases will have a reference
to the @GLIBCXX_3.4.11 version, andcode compiled against the new
libstdc++ will get a reference to the @@GLIBCXX_3.4.30 version.
libstdc++-v3/ChangeLog:
PR libstdc++/103382
* config/abi/pre/gnu.ver (GLIBCXX_3.4.11): Do not export old
symbol if .symver renaming is supported.
(GLIBCXX_3.4.30): Export new symbol if .symver renaming is
supported.
* doc/xml/manual/evolution.xml: Document change.
* doc/html/manual/api.html: Regenerate.
* include/bits/std_mutex.h (__condvar::wait, __condvar::wait_until):
Remove noexcept.
* include/std/condition_variable (condition_variable::wait):
Likewise.
* src/c++11/condition_variable.cc (condition_variable::wait):
Likewise.
* src/c++11/compatibility-condvar.cc (__nothrow_wait_cv::wait):
Define nothrow wrapper around std::condition_variable::wait and
export the old symbol as an alias to it.
* testsuite/30_threads/condition_variable/members/103382.cc: New test.
This introduces a new internal utility, std::__condvar, which is a
simplified form of std::condition_variable. It has no dependency on
<chrono> or std::unique_lock, which allows it to be used in
<bits/atomic_wait.h>.
This avoids repeating the #ifdef __GTHREAD_COND_INIT preprocessor
conditions and associated logic for initializing a __gthread_cond_t
correctly. It also encapsulates most of the __gthread_cond_xxx functions
as member functions of __condvar.
libstdc++-v3/ChangeLog:
* include/bits/atomic_timed_wait.h (__cond_wait_until_impl):
Do not define when _GLIBCXX_HAVE_LINUX_FUTEX is defined. Use
__condvar and mutex instead of __gthread_cond_t and
unique_lock<mutex>.
(__cond_wait_until): Likewise. Fix test for return value of
__cond_wait_until_impl.
(__timed_waiters::_M_do_wait_until): Use __condvar instead
of __gthread_cond_t.
* include/bits/atomic_wait.h: Remove <bits/unique_lock.h>
include. Only include <bits/std_mutex.h> if not using futexes.
(__platform_wait_max_value): Remove unused variable.
(__waiters::lock_t): Use lock_guard instead of unique_lock.
(__waiters::_M_cv): Use __condvar instead of __gthread_cond_t.
(__waiters::_M_do_wait(__platform_wait_t)): Likewise.
(__waiters::_M_notify()): Likewise. Use notify_one() if not
asked to notify all.
* include/bits/std_mutex.h (__condvar): New type.
* include/std/condition_variable (condition_variable::_M_cond)
(condition_variable::wait_until): Use __condvar instead of
__gthread_cond_t.
* src/c++11/condition_variable.cc (condition_variable): Define
default constructor and destructor as defaulted.
(condition_variable::wait, condition_variable::notify_one)
(condition_variable::notify_all): Forward to corresponding
member function of __condvar.
This will allow std::mutex and std::lock_guard to be used elsewhere in
the library without pulling in the whole of <chrono>.
Previously the whole of <bits/std_mutex.h> was conditional on the
_GLIBCXX_USE_C99_STDINT_TR1 macro, but only the std::unique_lock members
that use <chrono> facilities should depend on that. std::mutex only
needs to depend on _GLIBCXX_HAS_GTHREADS and std::lock_guard can be
defined unconditionally.
Some parts of <bits/std_mutex.h> and <mutex> are based on code in
<ext/concurrence.h> which dates from 2003. However, the std::unique_lock
implementation was added in 2008 by r135007, without using any earlier
code. Therefore the new header file has copyright years 2008-2018.
* include/Makefile.am: Add new <bits/unique_lock.h> header.
* include/Makefile.in: Regenerate.
* include/bits/std_mutex.h [!_GLIBCXX_USE_C99_STDINT_TR1] (mutex)
(lock_guard): Define independent of _GLIBCXX_USE_C99_STDINT_TR1.
(unique_lock): Move definition to ...
* include/bits/unique_lock.h: New header.
[!_GLIBCXX_USE_C99_STDINT_TR1] (unique_lock): Define unconditionally.
[_GLIBCXX_USE_C99_STDINT_TR1] (unique_lock(mutex_type&, time_point))
(unique_lock(mutex_type&, duration), unique_lock::try_lock_until)
(unique_lock::try_lock_for): Define only when <chrono> is usable.
* include/std/condition_variable: Include <bits/unique_lock.h>.
* include/std/mutex: Likewise.
From-SVN: r262963
Jakub Jelinek