ChapterÂ 30.Â Concurrency

ChapterÂ 30.Â Concurrency
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Option Flags	Description
`-std=c++98`	Use the 1998 ISO C++ standard plus amendments.
`-std=gnu++98`	As directly above, with GNU extensions.
`-std=c++11`	Use the 2011 ISO C++ standard.
`-std=gnu++11`	As directly above, with GNU extensions.
`-fexceptions`	See exception-free dialect
`-frtti`	As above, but RTTI-free dialect.
`-pthread` or `-pthreads`	For ISO C++11 <thread>, <future>, - <mutex>, or <condition_variable>.
`-fopenmp`	For parallel mode.

Option Flags

Description

-std=c++98

Use the 1998 ISO C++ standard plus amendments.

-std=gnu++98

As directly above, with GNU extensions.

-std=c++11

Use the 2011 ISO C++ standard.

-std=gnu++11

As directly above, with GNU extensions.

-fexceptions

See exception-free dialect

-frtti

As above, but RTTI-free dialect.

-pthread or -pthreads

For ISO C++11 <thread>, <future>, - <mutex>, or <condition_variable>.

-fopenmp

For parallel mode.

Option Flags	Description
`-std=c++98`	Use the 1998 ISO C++ standard plus amendments.
`-std=gnu++98`	As directly above, with GNU extensions.
`-std=c++11`	Use the 2011 ISO C++ standard.
`-std=gnu++11`	As directly above, with GNU extensions.
`-fexceptions`	See exception-free dialect
`-frtti`	As above, but RTTI-free dialect.
`-pthread` or `-pthreads`	For ISO C++11 + `<thread>`, + `<future>`, + `<mutex>`, + or `<condition_variable>`. +
`-latomic`	Linking to `libatomic` + is required for some uses of ISO C++11 + `<atomic>`. +
`-fopenmp`	For parallel mode.

Option Flags

Description

-std=c++98

Use the 1998 ISO C++ standard plus amendments.

-std=gnu++98

As directly above, with GNU extensions.

-std=c++11

Use the 2011 ISO C++ standard.

-std=gnu++11

As directly above, with GNU extensions.

-fexceptions

See exception-free dialect

-frtti

As above, but RTTI-free dialect.

-pthread or -pthreads

For ISO C++11 + <thread>, + <future>, + <mutex>, + or <condition_variable>. +

-latomic

Linking to libatomic + is required for some uses of ISO C++11 + <atomic>. +

-fopenmp

For parallel mode.

Implementation -

Using Builtin Atomic Functions +

Using Built-in Atomic Functions The functions for atomic operations described above are either @@ -197,9 +197,21 @@ capable) or by library fallbacks. Compiler intrinsics (builtins) are always preferred. However, as the compiler builtins for atomics are not universally implemented, using them directly is problematic, and can result in undefined -function calls. (An example of an undefined symbol from the use +function calls. + + +Prior to GCC 4.7 the older __sync intrinsics were used. +An example of an undefined symbol from the use of __sync_fetch_and_add on an unsupported host is a -missing reference to __sync_fetch_and_add_4.) +missing reference to __sync_fetch_and_add_4. + + +Current releases use the newer __atomic intrinsics, +which are implemented by library calls if the hardware doesn't support them. +Undefined references to functions like +__atomic_is_lock_free should be resolved by linking to +libatomic, which is usually +installed alongside libstdc++. In addition, on some hosts the compiler intrinsics are enabled diff --git a/libstdc++-v3/doc/xml/manual/using.xml b/libstdc++-v3/doc/xml/manual/using.xml index 3256c585a43..f6f615e1743 100644 --- a/libstdc++-v3/doc/xml/manual/using.xml +++ b/libstdc++-v3/doc/xml/manual/using.xml @@ -6,8 +6,7 @@

Command Options - The set of features available in the GNU C++ library is shaped - by + The set of features available in the GNU C++ library is shaped by several GCC Command Options. Options that impact libstdc++ are enumerated and detailed in the table below. @@ -64,8 +63,20 @@ -pthread or -pthreads - For ISO C++11 <thread>, <future>, - <mutex>, or <condition_variable>. + For ISO C++11 + <thread>, + <future>, + <mutex>, + or <condition_variable>. + + + + + -latomic + Linking to libatomic + is required for some uses of ISO C++11 + <atomic>. + @@ -779,8 +790,9 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe file c++config.h, which is generated during the libstdc++ configuration and build process. This file is then included when needed by files part of - the public libstdc++ API, like <ios>. Most of these macros - should not be used by consumers of libstdc++, and are reserved + the public libstdc++ API, like + <ios>. Most of these + macros should not be used by consumers of libstdc++, and are reserved for internal implementation use. These macros cannot be redefined. @@ -800,10 +812,10 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe __GLIBCXX__ The current version of - libstdc++ in compressed ISO date format, form of an unsigned + libstdc++ in compressed ISO date format, as an unsigned long. For details on the value of this particular macro for a - particular release, please consult this - document. + particular release, please consult the + ABI Policy and Guidelines appendix. @@ -816,14 +828,15 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe Configurable (or Not configurable) means that the symbol is initially chosen (or not) based on --enable/--disable options at library build and configure time - (documented here), with the - various --enable/--disable choices being translated to + (documented in + Configure), + with the various --enable/--disable choices being translated to #define/#undef). ABI means that changing from the default value may - mean changing the ABI of compiled code. In other words, these - choices control code which has already been compiled (i.e., in a + mean changing the ABI of compiled code. In other words, + these choices control code which has already been compiled (i.e., in a binary such as libstdc++.a/.so). If you explicitly #define or #undef these macros, the headers may see different code paths, but the libraries which you link against will not. @@ -854,7 +867,8 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe --enable-concept-checks. When defined, performs compile-time checking on certain template instantiations to detect violations of the requirements of the standard. This - is described in more detail here. + is described in more detail in + Compile Time Checks. @@ -862,31 +876,31 @@ g++ -Winvalid-pch -I. -include stdc++.h -H -g -O2 hello.cc -o test.exe Undefined by default. When defined, compiles user code using - the debug mode. + the debug mode. _GLIBCXX_DEBUG_PEDANTIC Undefined by default. When defined while compiling with - the debug mode, makes - the debug mode extremely picky by making the use of libstdc++ - extensions and libstdc++-specific behavior into errors. + the debug mode, makes + the debug mode extremely picky by making the use of libstdc++ + extensions and libstdc++-specific behavior into errors. _GLIBCXX_PARALLEL Undefined by default. When defined, compiles user code - using the parallel - mode. + using the parallel + mode. _GLIBCXX_PROFILE Undefined by default. When defined, compiles user code - using the profile - mode. + using the profile + mode. @@ -1248,13 +1262,16 @@ A quick read of the relevant part of the GCC all required macros to a compilation (if any such flags are required then you must provide the flag for all compilations not just linking) and link-library additions and/or replacements at - link time. The documentation is weak. Here is a quick summary - to display how ad hoc this is: On Solaris, both -pthreads and - -threads (with subtly different meanings) are honored. - On GNU/Linux x86, -pthread is honored. On FreeBSD, - -pthread is honored. Some other ports use other switches. - AFAIK, none of this is properly documented anywhere other than - in ``gcc -dumpspecs'' (look at lib and cpp entries). + link time. The documentation is weak. On several targets (including + GNU/Linux, Solaris and various BSDs) -pthread is honored. + Some other ports use other switches. + This is not well documented anywhere other than + in "gcc -dumpspecs" (look at the 'lib' and 'cpp' entries). + + + + Some uses of std::atomic also require linking + to libatomic.

@@ -1305,14 +1322,19 @@ gcc version 4.1.2 20070925 (Red Hat 4.1.2-33) Requisite command-line flags are used for atomic operations and threading. Examples of this include -pthread and -march=native, although specifics vary - depending on the host environment. See Machine + depending on the host environment. See + Command Options and + Machine Dependent Options. - An implementation of atomicity.h functions - exists for the architecture in question. See the internals documentation for more details. + An implementation of the + atomicity.h functions + exists for the architecture in question. See the + internals + documentation for more details.

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