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| author | Jonathan Wakely <jwakely@redhat.com> | 2019-07-11 20:43:32 +0100 |
|---|---|---|
| committer | Jonathan Wakely <redi@gcc.gnu.org> | 2019-07-11 20:43:32 +0100 |
| commit | f6822be73a5c0ca8e5f7af99b2827a14c9f5403e (patch) | |
| tree | 30f0bd222fd92da2b1e66c443618edcbfa77bb7a | |
| parent | a90fe12c80a13ffed9d5c775703788275d8b7c42 (diff) | |
| download | gcc-f6822be73a5c0ca8e5f7af99b2827a14c9f5403e.zip gcc-f6822be73a5c0ca8e5f7af99b2827a14c9f5403e.tar.gz gcc-f6822be73a5c0ca8e5f7af99b2827a14c9f5403e.tar.bz2 | |
Improve docs for --enable-libstdcxx-time=rt
* doc/xml/manual/configure.xml: Improve documentation of
--enable-libstdcxx-time option.
From-SVN: r273421
| -rw-r--r-- | libstdc++-v3/ChangeLog | 3 | ||||
| -rw-r--r-- | libstdc++-v3/doc/xml/manual/configure.xml | 20 |
2 files changed, 16 insertions, 7 deletions
diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 688615f..69f5b86 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,5 +1,8 @@ 2019-07-11 Jonathan Wakely <jwakely@redhat.com> + * doc/xml/manual/configure.xml: Improve documentation of + --enable-libstdcxx-time option. + * include/bits/atomic_base.h (__atomic_impl): New namespace for wrappers around atomic built-ins. (__atomic_float, __atomic_ref): New class templates for use as base diff --git a/libstdc++-v3/doc/xml/manual/configure.xml b/libstdc++-v3/doc/xml/manual/configure.xml index d296c8d..58587e8 100644 --- a/libstdc++-v3/doc/xml/manual/configure.xml +++ b/libstdc++-v3/doc/xml/manual/configure.xml @@ -166,18 +166,24 @@ <varlistentry><term><code>--enable-libstdcxx-time=OPTION</code></term> <listitem><para>Enables link-type checks for the availability of the - clock_gettime clocks, used in the implementation of [time.clock], - and of the nanosleep and sched_yield functions, used in the + <function>clock_gettime</function> clocks, used in the implementation + of [time.clock], and of the <function>nanosleep</function> and + <function>sched_yield</function> functions, used in the implementation of [thread.thread.this] of the 2011 ISO C++ standard. The choice OPTION=yes checks for the availability of the facilities in libc and libposix4. In case it's needed the latter is also linked - to libstdc++ as part of the build process. OPTION=rt also searches - (and, if needed, links) librt. Note that the latter is not always - desirable because, in glibc, for example, in turn it triggers the - linking of libpthread too, which activates locking, a large overhead - for single-thread programs. OPTION=no skips the tests completely. + to libstdc++ as part of the build process. OPTION=rt also checks in + librt (and, if it's needed, links to it). Note that linking to librt + is not always desirable because for glibc it requires linking to + libpthread too, which causes all reference counting to use atomic + operations, resulting in a potentially large overhead for + single-threaded programs. OPTION=no skips the tests completely. The default is OPTION=auto, which skips the checks and enables the features only for targets known to support them. + For Linux targets, if <function>clock_gettime</function> is not used + then the [time.clock] implementation will use a system call to access + the realtime and monotonic clocks, which is significantly slower than + the C library's <function>clock_gettime</function> function. </para> </listitem></varlistentry> |