Chris@50: // Copyright (c) 2014, Jason Choy <jjwchoy@gmail.com>
Chris@50: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
Chris@50: // Licensed under the MIT License:
Chris@50: //
Chris@50: // Permission is hereby granted, free of charge, to any person obtaining a copy
Chris@50: // of this software and associated documentation files (the "Software"), to deal
Chris@50: // in the Software without restriction, including without limitation the rights
Chris@50: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
Chris@50: // copies of the Software, and to permit persons to whom the Software is
Chris@50: // furnished to do so, subject to the following conditions:
Chris@50: //
Chris@50: // The above copyright notice and this permission notice shall be included in
Chris@50: // all copies or substantial portions of the Software.
Chris@50: //
Chris@50: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
Chris@50: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
Chris@50: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
Chris@50: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
Chris@50: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
Chris@50: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
Chris@50: // THE SOFTWARE.
Chris@50: 
Chris@50: #ifndef KJ_THREADLOCAL_H_
Chris@50: #define KJ_THREADLOCAL_H_
Chris@50: 
Chris@50: #if defined(__GNUC__) && !KJ_HEADER_WARNINGS
Chris@50: #pragma GCC system_header
Chris@50: #endif
Chris@50: // This file declares a macro `KJ_THREADLOCAL_PTR` for declaring thread-local pointer-typed
Chris@50: // variables.  Use like:
Chris@50: //     KJ_THREADLOCAL_PTR(MyType) foo = nullptr;
Chris@50: // This is equivalent to:
Chris@50: //     thread_local MyType* foo = nullptr;
Chris@50: // This can only be used at the global scope.
Chris@50: //
Chris@50: // AVOID USING THIS.  Use of thread-locals is discouraged because they often have many of the same
Chris@50: // properties as singletons: http://www.object-oriented-security.org/lets-argue/singletons
Chris@50: //
Chris@50: // Also, thread-locals tend to be hostile to event-driven code, which can be particularly
Chris@50: // surprising when using fibers (all fibers in the same thread will share the same threadlocals,
Chris@50: // even though they do not share a stack).
Chris@50: //
Chris@50: // That said, thread-locals are sometimes needed for runtime logistics in the KJ framework.  For
Chris@50: // example, the current exception callback and current EventLoop are stored as thread-local
Chris@50: // pointers.  Since KJ only ever needs to store pointers, not values, we avoid the question of
Chris@50: // whether these values' destructors need to be run, and we avoid the need for heap allocation.
Chris@50: 
Chris@50: #include "common.h"
Chris@50: 
Chris@50: #if !defined(KJ_USE_PTHREAD_THREADLOCAL) && defined(__APPLE__)
Chris@50: #include "TargetConditionals.h"
Chris@50: #if TARGET_OS_IPHONE
Chris@50: // iOS apparently does not support __thread (nor C++11 thread_local).
Chris@50: #define KJ_USE_PTHREAD_TLS 1
Chris@50: #endif
Chris@50: #endif
Chris@50: 
Chris@50: #if KJ_USE_PTHREAD_TLS
Chris@50: #include <pthread.h>
Chris@50: #endif
Chris@50: 
Chris@50: namespace kj {
Chris@50: 
Chris@50: #if KJ_USE_PTHREAD_TLS
Chris@50: // If __thread is unavailable, we'll fall back to pthreads.
Chris@50: 
Chris@50: #define KJ_THREADLOCAL_PTR(type) \
Chris@50:   namespace { struct KJ_UNIQUE_NAME(_kj_TlpTag); } \
Chris@50:   static ::kj::_::ThreadLocalPtr< type, KJ_UNIQUE_NAME(_kj_TlpTag)>
Chris@50: // Hack:  In order to ensure each thread-local results in a unique template instance, we declare
Chris@50: //   a one-off dummy type to use as the second type parameter.
Chris@50: 
Chris@50: namespace _ {  // private
Chris@50: 
Chris@50: template <typename T, typename>
Chris@50: class ThreadLocalPtr {
Chris@50:   // Hacky type to emulate __thread T*.  We need a separate instance of the ThreadLocalPtr template
Chris@50:   // for every thread-local variable, because we don't want to require a global constructor, and in
Chris@50:   // order to initialize the TLS on first use we need to use a local static variable (in getKey()).
Chris@50:   // Each template instance will get a separate such local static variable, fulfilling our need.
Chris@50: 
Chris@50: public:
Chris@50:   ThreadLocalPtr() = default;
Chris@50:   constexpr ThreadLocalPtr(decltype(nullptr)) {}
Chris@50:   // Allow initialization to nullptr without a global constructor.
Chris@50: 
Chris@50:   inline ThreadLocalPtr& operator=(T* val) {
Chris@50:     pthread_setspecific(getKey(), val);
Chris@50:     return *this;
Chris@50:   }
Chris@50: 
Chris@50:   inline operator T*() const {
Chris@50:     return get();
Chris@50:   }
Chris@50: 
Chris@50:   inline T& operator*() const {
Chris@50:     return *get();
Chris@50:   }
Chris@50: 
Chris@50:   inline T* operator->() const {
Chris@50:     return get();
Chris@50:   }
Chris@50: 
Chris@50: private:
Chris@50:   inline T* get() const {
Chris@50:     return reinterpret_cast<T*>(pthread_getspecific(getKey()));
Chris@50:   }
Chris@50: 
Chris@50:   inline static pthread_key_t getKey() {
Chris@50:     static pthread_key_t key = createKey();
Chris@50:     return key;
Chris@50:   }
Chris@50: 
Chris@50:   static pthread_key_t createKey() {
Chris@50:     pthread_key_t key;
Chris@50:     pthread_key_create(&key, 0);
Chris@50:     return key;
Chris@50:   }
Chris@50: };
Chris@50: 
Chris@50: }  // namespace _ (private)
Chris@50: 
Chris@50: #elif __GNUC__
Chris@50: 
Chris@50: #define KJ_THREADLOCAL_PTR(type) static __thread type*
Chris@50: // GCC's __thread is lighter-weight than thread_local and is good enough for our purposes.
Chris@50: 
Chris@50: #else
Chris@50: 
Chris@50: #define KJ_THREADLOCAL_PTR(type) static thread_local type*
Chris@50: 
Chris@50: #endif // KJ_USE_PTHREAD_TLS
Chris@50: 
Chris@50: }  // namespace kj
Chris@50: 
Chris@50: #endif  // KJ_THREADLOCAL_H_