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Define new filesystem::__file_clock type 

In C++17 the clock used for filesystem::file_time_type is unspecified,
allowing it to be chrono::system_clock. The C++2a draft requires it to
be a distinct type, with additional member functions to convert to/from
other clocks (either the system clock or UTC). In order to avoid an ABI
change later, this patch defines a new distinct type now, which will be
used for std::chrono::file_clock later.

	* include/bits/fs_fwd.h (__file_clock): Define new clock.
	(file_time_type): Redefine in terms of __file_clock.
	* src/filesystem/ops-common.h (file_time): Add FIXME comment about
	overflow.
	* src/filesystem/std-ops.cc (is_set(perm_options, perm_options)): Give
	internal linkage.
	(internal_file_lock): New helper type for accessing __file_clock.
	(do_copy_file): Use internal_file_lock to convert system time to
	file_time_type.
	(last_write_time(const path&, error_code&)): Likewise.
	(last_write_time(const path&, file_time_type, error_code&)): Likewise.

From-SVN: r267602
This commit is contained in:
Jonathan Wakely 2019-01-05 20:03:22 +00:00 committed by Jonathan Wakely
parent d06f73a387
commit beb04ce9d4
4 changed files with 102 additions and 6 deletions
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14
libstdc++-v3/ChangeLog
View File

@ -1,3 +1,17 @@
2019-01-05 Jonathan Wakely <jwakely@redhat.com>
* include/bits/fs_fwd.h (__file_clock): Define new clock.
(file_time_type): Redefine in terms of __file_clock.
* src/filesystem/ops-common.h (file_time): Add FIXME comment about
overflow.
* src/filesystem/std-ops.cc (is_set(perm_options, perm_options)): Give
internal linkage.
(internal_file_lock): New helper type for accessing __file_clock.
(do_copy_file): Use internal_file_lock to convert system time to
file_time_type.
(last_write_time(const path&, error_code&)): Likewise.
(last_write_time(const path&, file_time_type, error_code&)): Likewise.
2019-01-04 Jonathan Wakely <jwakely@redhat.com>
* config/abi/pre/gnu.ver (GLIBCXX_3.4.21): Make patterns less greedy

44
libstdc++-v3/include/bits/fs_fwd.h
View File

@ -294,7 +294,49 @@ _GLIBCXX_END_NAMESPACE_CXX11
operator^=(directory_options& __x, directory_options __y) noexcept
{ return __x = __x ^ __y; }
using file_time_type = std::chrono::system_clock::time_point;
struct __file_clock
{
using duration = chrono::nanoseconds;
using rep = duration::rep;
using period = duration::period;
using time_point = chrono::time_point<__file_clock>;
static constexpr bool is_steady = false;
static time_point
now() noexcept
{ return _S_from_sys(chrono::system_clock::now()); }
private:
using __sys_clock = chrono::system_clock;
// This clock's (unspecified) epoch is 2174-01-01 00:00:00 UTC.
// A signed 64-bit duration with nanosecond resolution gives roughly
// +/- 292 years, which covers the 1901-2446 date range for ext4.
static constexpr chrono::seconds _S_epoch_diff{6437664000};
protected:
// For internal use only
template<typename _Dur>
static
chrono::time_point<__file_clock, _Dur>
_S_from_sys(const chrono::time_point<__sys_clock, _Dur>& __t) noexcept
{
using __file_time = chrono::time_point<__file_clock, _Dur>;
return __file_time{__t.time_since_epoch()} - _S_epoch_diff;
}
// For internal use only
template<typename _Dur>
static
chrono::time_point<__sys_clock, _Dur>
_S_to_sys(const chrono::time_point<__file_clock, _Dur>& __t) noexcept
{
using __sys_time = chrono::time_point<__sys_clock, _Dur>;
return __sys_time{__t.time_since_epoch()} + _S_epoch_diff;
}
};
using file_time_type = __file_clock::time_point;
// operational functions

18
libstdc++-v3/src/filesystem/ops-common.h
View File

@ -158,6 +158,24 @@ namespace __gnu_posix
nanoseconds ns{};
#endif
// FIXME
// There are possible timespec values which will overflow
// chrono::system_clock::time_point but would not overflow
// __file_clock::time_point, due to its different epoch.
//
// By checking for overflow of the intermediate system_clock::duration
// type, we report an error for values which are actually representable
// in the file_time_type result type.
//
// Howard Hinnant's solution for this problem is to use
// duration<__int128>{s} + ns, which doesn't overflow.
// An alternative would be to do the epoch correction on s before
// the addition, and then go straight to file_time_type instead of
// going via chrono::system_clock::time_point.
//
// (This only applies to the C++17 Filesystem library, because for the
// Filesystem TS we don't have a distinct __file_clock, we just use the
// system clock for file timestamps).
if (s >= (nanoseconds::max().count() / 1e9))
{
ec = std::make_error_code(std::errc::value_too_large); // EOVERFLOW

32
libstdc++-v3/src/filesystem/std-ops.cc
View File

@ -268,13 +268,32 @@ fs::copy(const path& from, const path& to, copy_options options)
namespace std::filesystem
{
// Need this as there's no 'perm_options::none' enumerator.
inline bool is_set(fs::perm_options obj, fs::perm_options bits)
static inline bool is_set(fs::perm_options obj, fs::perm_options bits)
{
return (obj & bits) != fs::perm_options{};
}
}
#ifdef _GLIBCXX_HAVE_SYS_STAT_H
namespace
{
struct internal_file_clock : fs::__file_clock
{
using __file_clock::_S_to_sys;
using __file_clock::_S_from_sys;
static fs::file_time_type
from_stat(const fs::stat_type& st, std::error_code& ec) noexcept
{
const auto sys_time = fs::file_time(st, ec);
if (sys_time == sys_time.min())
return fs::file_time_type::min();
return _S_from_sys(sys_time);
}
};
}
#ifdef NEED_DO_COPY_FILE
bool
fs::do_copy_file(const path::value_type* from, const path::value_type* to,
@ -348,10 +367,10 @@ fs::do_copy_file(const path::value_type* from, const path::value_type* to,
}
else if (options.update)
{
const auto from_mtime = file_time(*from_st, ec);
const auto from_mtime = internal_file_clock::from_stat(*from_st, ec);
if (ec)
return false;
if ((from_mtime <= file_time(*to_st, ec)) || ec)
if ((from_mtime <= internal_file_clock::from_stat(*to_st, ec)) || ec)
return false;
}
else if (!options.overwrite)
@ -1122,7 +1141,10 @@ fs::last_write_time(const path& p)
fs::file_time_type
fs::last_write_time(const path& p, error_code& ec) noexcept
{
return do_stat(p, ec, [&ec](const auto& st) { return file_time(st, ec); },
return do_stat(p, ec,
[&ec](const auto& st) {
return internal_file_clock::from_stat(st, ec);
},
file_time_type::min());
}
@ -1139,7 +1161,7 @@ void
fs::last_write_time(const path& p __attribute__((__unused__)),
file_time_type new_time, error_code& ec) noexcept
{
auto d = new_time.time_since_epoch();
auto d = internal_file_clock::_S_to_sys(new_time).time_since_epoch();
auto s = chrono::duration_cast<chrono::seconds>(d);
#if _GLIBCXX_USE_UTIMENSAT
auto ns = chrono::duration_cast<chrono::nanoseconds>(d - s);