folly::SingletonThreadLocal< T, Tag, Make, TLTag > Class Template Reference

#include <SingletonThreadLocal.h>

Classes
struct	Node
struct	Wrapper

Static Public Member Functions
FOLLY_EXPORT static FOLLY_ALWAYS_INLINE T &	get ()
static WrapperTL::Accessor	accessAllThreads ()

Private Types
using	NodeBase = boost::intrusive::list_base_hook< boost::intrusive::link_mode< boost::intrusive::auto_unlink >>
using	List = boost::intrusive::list< Node, boost::intrusive::constant_time_size< false >>
using	WrapperTL = ThreadLocal< Wrapper, TLTag >

Private Member Functions
	SingletonThreadLocal ()=delete

Static Private Member Functions
FOLLY_EXPORT static FOLLY_NOINLINE WrapperTL &	getWrapperTL ()
static FOLLY_NOINLINE Wrapper &	getWrapper ()

Detailed Description

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>
class folly::SingletonThreadLocal< T, Tag, Make, TLTag >

SingletonThreadLocal

Useful for a per-thread leaky-singleton model in libraries and applications.

By "leaky" it is meant that the T instances held by the instantiation SingletonThreadLocal<T> will survive until their owning thread exits. Therefore, they can safely be used before main() begins and after main() ends, and they can also safely be used in an application that spawns many temporary threads throughout its life.

Example:

struct UsefulButHasExpensiveCtor { UsefulButHasExpensiveCtor(); // this is expensive Result operator()(Arg arg); };

Result useful(Arg arg) { using Useful = UsefulButHasExpensiveCtor; auto& useful = folly::SingletonThreadLocal<Useful>::get(); return useful(arg); }

As an example use-case, the random generators in <random> are expensive to construct. And their constructors are deterministic, but many cases require that they be randomly seeded. So folly::Random makes good canonical uses of folly::SingletonThreadLocal so that a seed is computed from the secure random device once per thread, and the random generator is constructed with the seed once per thread.

Keywords to help people find this class in search: Thread Local Singleton ThreadLocalSingleton

Definition at line 68 of file SingletonThreadLocal.h.

Member Typedef Documentation

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

using folly::SingletonThreadLocal< T, Tag, Make, TLTag >::List = boost::intrusive::list<Node, boost::intrusive::constant_time_size<false>>

private

Definition at line 95 of file SingletonThreadLocal.h.

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

using folly::SingletonThreadLocal< T, Tag, Make, TLTag >::NodeBase = boost::intrusive::list_base_hook< boost::intrusive::link_mode<boost::intrusive::auto_unlink>>

private

Definition at line 73 of file SingletonThreadLocal.h.

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

using folly::SingletonThreadLocal< T, Tag, Make, TLTag >::WrapperTL = ThreadLocal<Wrapper, TLTag>

private

Definition at line 131 of file SingletonThreadLocal.h.

Constructor & Destructor Documentation

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

folly::SingletonThreadLocal< T, Tag, Make, TLTag >::SingletonThreadLocal ( )

privatedelete

Member Function Documentation

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

static WrapperTL::Accessor folly::SingletonThreadLocal< T, Tag, Make, TLTag >::accessAllThreads ( )

inlinestatic

Definition at line 165 of file SingletonThreadLocal.h.

References folly::ThreadLocal< T, Tag, AccessMode >::accessAllThreads(), and folly::SingletonThreadLocal< T, Tag, Make, TLTag >::getWrapperTL().

                                                       {
    return getWrapperTL().accessAllThreads();
  }

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

FOLLY_EXPORT static FOLLY_ALWAYS_INLINE T& folly::SingletonThreadLocal< T, Tag, Make, TLTag >::get ( )

inlinestatic

Definition at line 155 of file SingletonThreadLocal.h.

References folly::SingletonThreadLocal< T, Tag, Make, TLTag >::Node::cache, FOLLY_LIKELY, folly::settings::detail::getSlow(), and folly::SingletonThreadLocal< T, Tag, Make, TLTag >::getWrapper().

Referenced by proxygen::HTTPMessage::formatDateHeader(), folly::fibers::FiberManager::registerAlternateSignalStack(), and TEST().

                                                   {
#ifdef FOLLY_TLS
    static thread_local Wrapper* cache;
    return FOLLY_LIKELY(!!cache) ? *cache : getSlow(cache);
#else
    return getWrapper();
#endif
  }

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

static FOLLY_NOINLINE Wrapper& folly::SingletonThreadLocal< T, Tag, Make, TLTag >::getWrapper ( )

inlinestaticprivate

Definition at line 140 of file SingletonThreadLocal.h.

References folly::SingletonThreadLocal< T, Tag, Make, TLTag >::Node::cache, check(), FOLLY_NOINLINE, folly::settings::detail::getSlow(), folly::SingletonThreadLocal< T, Tag, Make, TLTag >::getWrapperTL(), folly::SingletonThreadLocal< T, Tag, Make, TLTag >::Node::stale, and folly::T.

Referenced by folly::SingletonThreadLocal< T, Tag, Make, TLTag >::get(), and folly::SingletonThreadLocal< T, Tag, Make, TLTag >::Node::Node().

                                              {
    return *getWrapperTL();
  }

template<typename T, typename Tag = detail::DefaultTag, typename Make = detail::DefaultMake<T>, typename TLTag = _t<std::conditional< std::is_same<Tag, detail::DefaultTag>::value, void, Tag>>>

FOLLY_EXPORT static FOLLY_NOINLINE WrapperTL& folly::SingletonThreadLocal< T, Tag, Make, TLTag >::getWrapperTL ( )

inlinestaticprivate

Definition at line 135 of file SingletonThreadLocal.h.

Referenced by folly::SingletonThreadLocal< T, Tag, Make, TLTag >::accessAllThreads(), and folly::SingletonThreadLocal< T, Tag, Make, TLTag >::getWrapper().

                                                               {
    static auto& entry = *detail::createGlobal<WrapperTL, Tag>();
    return entry;
  }

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The documentation for this class was generated from the following file:

• proxygen/folly/folly/SingletonThreadLocal.h